Abbreviation for yysecond.

For basic rate access in an Integrated Services Digital Network (ISDN) environment, a user-to-network interface reference point that (a) is characterized by a 4-wire, 144-kb/s (2B+D) user rate, (b) serves as a universal interface between ISDN terminals or terminal adapters and the network channel termination, (c) allows a variety of terminal types and subscriber networks, such as PBXs, local area… (Read More →)

The conceptual reference point dividing the TEI (terminal endpoint identifier) and the NT2 (network termination 2) in a particular ISDN access arrangement. [T1.615-1992]

Serving-Call Session Control Function

Abbreviation for store-and-forward.

Services & System Aspects

Services & System Aspects

1. service access code

System Architecture Evolution

[A] statement affixed to a computer output or printout that states the highest classification being processed at the time the product was produced and requires control of the product, at that level, until determination of the true classification by an authorized person. Synonym [in INFOSEC] banner. [INFOSEC-99]

Any radiocommunication service used permanently or temporarily for the safeguarding of human life and property. [NTIA] [RR]

Service Area Interface (also called crossbox, FDI, JWI)

Key intended for off-the-air demonstration use only. [INFOSEC-99]

Data in which the information content exists only for instantaneous values measured or determined at or for discrete intervals.
Note: Sampled data can be analog or digital. [After SMPTE]

See signal sampling.

See sampling rate.

The reciprocal of the sampling rate, i.e., the interval between corresponding points on two successive sampling pulses of the sampling signal.

The number of samples taken per unit time, i.e., the rate at which signals are sampled for subsequent use, such as for modulation, coding, and quantization. Deprecated synonym sampling frequency.

Synonym Nyquist's theorem.

Storage Area Network

[In INFOSEC, the] process to remove information from media such that data recovery is not possible. It includes removing all classified labels, markings, and activity logs. [INFOSEC-99]

Of a recording medium, erasing or overwriting all data in such a manner that it cannot be recovered, even by extraordinary, e.g., laboratory, means.
Note: Sanitizing is distinguished from simply "deleting" or "erasing" data. For example, a software-based deletion command may simply mark a file or block of data to the effect that it may be overwritten during a subsequent… (Read More →)

Abbreviation for service access point.

Serial Advanced Technology Attachment

A body which revolves around another body of preponderant mass and which has a motion primarily and permanently determined by the force of attraction of that other body. [NTIA] [RR]
Note: A parent body and its satellite revolve about their common center of gravity.

In satellite communications systems, the establishment of contact with a communications satellite space station.
Note: An example of satellite access is access at the moment at which an Earth station commences to use a satellite space station as a signal repeater, i.e., to use its transponder. Each radio frequency (rf) carrier that is relayed by a satellite space station at… (Read More →)

A telecommunications service provided via one or more satellite relays and their associated uplinks and downlinks.

1. A satellite-based direct-broadcast radio service in which digitally encoded audio entertainment material is broadcast to Earth-based receivers, either directly from an orbiting satellite, or--in cases in which the receiver is in a shielded location--from the satellite to the receiver via a repeater station.
2. A radiocommunication service in which audio programming is digitally transmitted by one or more space… (Read More →)

Synonym Earth terminal.

An Earth station in the mobile-satellite service the emissions of which are intended to facilitate search and rescue operations. [RR]

A radio link between a transmitting Earth station and a receiving Earth station through one satellite. A satellite link comprises one uplink and one downlink. [NTIA] [RR]

1. A satellite system or a part of a satellite system, consisting of only one satellite and the cooperating Earth stations. [RR]
2. A satellite system, or part of a satellite system, and the cooperating Earth stations.

See satellite PBX.

A PBX system that is not equipped with attendant positions, and is associated with an attended main PBX system.
Note: The main attendant provides attendant functions for the satellite system.

See period (of a satellite).

An active or passive satellite repeater that relays signals between two terminals.

A space system using one or more artificial Earth satellites. [NTIA] [RR] [47CFR]

Structure-Agnostic Time Division Multiplexing over Packet

1. In a communications system, the condition in which a component of the system has reached its maximum traffic handling capacity.
Note: Saturation is equivalent to one erlang per circuit.
2. The point at which the output of a linear device, such as a linear amplifier, deviates significantly from being a linear function of the input when the input signal… (Read More →)

Session Border Control

1. The degree to which video and image formats can be sized in systematic proportions for distribution over communications channels of varying capacities. [After SMPTE]
2. The ease with which software can be transferred from one graduated series of application platforms to another [POSIX.0].

1. To examine sequentially, part by part.
2. To examine every reference in every entry in a file routinely as part of a retrieval scheme.
3. In radar, one complete rotation of the interrogating antenna.
4. In SONAR, to search 360° or a specific search sector by the use of phased array of transducers.
5. To sweep, i.e., rotate, a… (Read More →)

1. The line produced on a recording medium frame by a single sweep of a scanner. [JP1]
2. Synonym scanning line.

In automatic link establishment (ALE) radios, the undesired condition in which the normal process of (a) scanning radio channels, (b) stopping on the desired channel, or (c) returning to scan is terminated by the equipment.

1. In computer graphics, a device that sequentially samples and records digitally the color and intensity of successive elements of an object or image (e.g., a flat, paper object such as a photograph or drawing), for digital storage, transmission, or processing.
Note: The collected data are usually stored in one of several computer graphics formats.
2. In television technology, a… (Read More →)

1. In telecommunications systems, examination of traffic activity to determine whether further processing is required.
Note: Scanning is usually performed periodically.
2. In television, facsimile, and picture transmission, the process of successively analyzing the colors and densities of the object according to a predetermined pattern.
3. The process of tuning a device through a predetermined range of frequencies in prescribed… (Read More →)

In facsimile transmitting equipment, the scanning of an object, such as a message surface or the developed plane in the case of a drum, along parallel lines in a specified pattern.
Note 1: The scanning direction is equivalent to scanning over a right-hand helix on a drum.
Note 2: The orientation of the message on the scanning plane will depend… (Read More →)

In facsimile systems, the total of the areas that are actually explored by the scanning spot during the scanning of the object by the transmitter or during scanning of the record medium by the receiver. [From Weik '89]

In an imaging system, the path traversed by a scanning spot during a single line sweep.

In facsimile, the frequency at which a fixed line perpendicular to the direction of scanning is crossed by a scanning spot.
Note: The scanning line frequency is equivalent to drum speed in some mechanical systems. Synonym scanning line rate.

In facsimile systems, the total length of a scanning line, equal to the spot speed divided by the scanning line frequency.
Note: The scanning line length is usually greater than the length of the available line.

In facsimile systems, the time interval between (a) the instant at which the scanning spot probes or writes to a given spot on one scanning line, and (b) the instant at which the scanning spot probes or writes to the corresponding spot on the next scanning line.

Synonym scanning line frequency.

The distance between the centers of consecutive scanning lines.

In facsimile and television systems, the rate of displacement of the scanning spot along the scanning line.

In facsimile systems, the area on the object, i.e., the original, covered instantaneously by the pickup system of the scanner.

See scattering.

Of a wave propagating in a material medium, a phenomenon in which the direction, frequency, or polarization of the wave is changed when the wave encounters discontinuities in the medium, or interacts with the material at the atomic or molecular level.
Note: Scattering results in a disordered or random change in the incident energy distribution.

In the microstructure of a transmission medium, a site at which electromagnetic waves are scattered.
Note 1: Examples of scattering centers are vacancy defects; interstitial defects; inclusions, such as a gas molecules, hydroxide ions, iron ions, and trapped water molecules; and microcracks or fractures in dielectric waveguides.
Note 2: Scattering centers are frozen in the medium when it solidifies and… (Read More →)

The factor that expresses the attenuation caused by scattering, e.g., of radiant or acoustic energy, during its passage through a medium.
Note: The scattering coefficient is usually expressed in units of reciprocal distance.

The area of an incident wavefront, at a reflecting surface or medium, such as an object in space, through which will pass radiant energy, that, if isotropically scattered from that point, would produce the same power at a given receiver as is actually provided by the entire reflecting surface. [From Weik '89]

The part of the transmission (power) loss that results from scattering within a transmission medium or from roughness of a reflecting surface.

To search, without authorization, through residual data to acquire sensitive information. [2382-pt.8]

Searching through object residue to acquire data. [INFOSEC-99]

Abbreviation for specialized common carrier.

Synchronous Code Division Multiple Access

In video, synonymous with clip.

Video imagery in which consecutive frames are highly uncorrelated.

In video systems, the perceived impairments associated with a scene cut.

Service Control Function

1. A diagram, drawing, or sketch that details the elements of a system, such as the elements of an electrical circuit or the elements of a logic diagram for a computer or communications system.
2. Pertaining to a diagram, drawing, or sketch that details the elements of a system, such as the elements of an electrical circuit or the elements… (Read More →)

Service Capability Interaction Manager

In electromagnetic wave propagation, a small random fluctuation of the received field strength about its mean value.
Note: Scintillation effects become more significant as the frequency of the propagating wave increases.

A device that transposes or inverts signals or otherwise encodes a message at the transmitter to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device.
Note: Scramblers usually use a fixed algorithm or mechanism. However, a scrambler provides communications privacy that is inadequate for classified traffic.

Temporary key storage in crypto-equipment. [INFOSEC-99]

Synonym bang.

1. In a telecommunications, computing, or data processing system, to examine entities that are being processed to determine their suitability for further processing.
2. A nonferrous metallic mesh used to provide electromagnetic shielding.
3. To reduce undesired electromagnetic signals and noise by enclosing devices in electrostatic or electromagnetic shields.
4. A viewing surface, such as that of a cathode ray… (Read More →)

In computers, the process or act by which the data currently displayed on a monitor, usually representing a single frame of information, are stored or processed in a graphical format.
Note: A screen capture thus represents an instantaneous "snapshot" of the state of the display.

A subnetwork that permits access from both untrusted external networks and from trusted internal networks, but does not permit traffic flow between the two. [2382-pt.35]

Synonym bastion host.

A network router capable of discriminating network-based traffic on the protocol type and the value of the protocol fields within the packet. [2382-pt.35]

A relatively short computer program that performs one specific task.
Note: A script is normally used to automate complex or advanced features or procedures within a system. Scripts are commonly used to process user information from Web pages (for example, a search engine is a script).

A programming language supported by and specific to a particular program.
Note: A scripting program is normally used to automate complex or advanced features or procedures within the program. [After Bahorsky]

In a display device, to move the display window of the screen vertically to view the contents of a stored document.
Note: Scrolling may be performed continuously or incrementally.

A terminal in which the data are displayed (or pass by) a line at a time.

Acronym for small computer system interface. An intelligent interface device that expands a microprocessor (CPU) bus to facilitate connections to multiple peripherals (e.g., CD-ROM drives, hard drives, or scanners) and exchange data with those peripherals via a separate communications bus.
Note 1: The original SCSI was capable of supporting up to 7 devices at a data rate of 5 Mb/s… (Read More →)

Society of Cable and Television Engineers

The server side logic of the "Services Discovery" process, which can either be implemented by a dedicated server or it can reside on an IPTV Application server (thus be collected with other IPTV functions).

See satellite digital audio radio service.

Synchronous Digital Hierarchy

Abbreviation for synchronous data link control. A proprietary, code-independent, link-control protocol.

Standards Development Organization

1. Service Delivery Platform,
2. Session Description Organization.

Software Defined Radio

Standard Definition Television

Service Enablers

1. A checksum, which may be cryptographic, computed over some data to provide integrity for that data [ECMA138].
2. A cryptographic checkvalue that supports integrity but does not protect against forgery by the recipient (i.e., it does not support non-repudiation). When a seal is associated with a data element, that data element is 'sealed' [10181-1].

A specialized program that facilitates information retrieval from large segments of the Internet.
Note 1: Search engines attempt to help a user locate desired information or resources by seeking matches to user-specified key words. The usual method for finding and isolating this information is to compile and maintain an index of Web resources that can be queried for the key… (Read More →)

See bot, droid.

In data processing systems, the time interval required to locate a particular data element, record, or file in a storage device.

Acronym for système electronique couleur avec memoire. A television signal standard (625 lines, 50 Hz, 220 V primary power) used in France, eastern European countries, the former USSR, and some African countries.

In the International System of Units (SI), the time interval equal to 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.

1. Dialtone presented to the call originator after an access code has been dialed for access to a second, outside, telecommunications system or service.
2. Dialtone returned to the call originator after she/he has dialed an access number and has reached a switch providing access to modem, to a fax machine, to another telephone, etc.

Of silica-based optical fibers, the transmission window at approximately
1. 3 m.
Note: The second window is the minimum-dispersion window in silica-based glasses. [After FAA]

In a system in which two channels share a common interface, a channel that has a lower data signaling rate (DSR) capacity than the primary channel.

Particles or radiation, such as photons, Compton recoil electrons, delta rays, secondary cosmic rays, and secondary electrons, that are produced by the action of primary radiation on matter.

A frequency standard that does not have inherent accuracy, and therefore must be calibrated against a primary frequency standard.
Note: Secondary standards include crystal oscillators and rubidium standards. A crystal oscillator depends for its frequency on its physical dimensions, which vary with fabrication and environmental conditions. A rubidium standard is a secondary standard even though it uses atomic transitions, because… (Read More →)

A radiodetermination system based on the comparison of reference signals with radio signals retransmitted from the position to be determined. [NTIA] [RR]
Note: An example of secondary radar is the transponder-based surveillance of aircraft. Synonym secondary surveillance radar.

See secondary emission.

[T]he service area of a broadcast station served by the skywave and not subject to objectionable interference and in which the signal is subject to intermittent variations in strength. [47CFR]

In a communications network, a station that (a) is responsible for performing unbalanced link-level operations as instructed by the primary station and (b) interprets received commands and generates responses.

Synonym secondary radar.

A time standard that requires periodic calibration against a primary time standard.

Acronym for secure voice cord board. A desk-mounted patch panel that provides the capability for controlling (a) sixteen 50-kb/s wideband or sixteen 2400-b/s narrowband user lines and (b) 5 narrowband trunks to DSN or other narrowband facilities.

1. A key that is intended for use by a limited number of correspondents for encryption and decryption. [2382-pt.8]
2. In a symmetric cryptographic algorithm the key shared between two entities [10181-1].
3. In a symmetric encipherment algorithm the key shared between two entities [10181-2].

Any encryption process that (a) depends on only one encryption key, known only to message senders and receivers, and (b) is used to both encode and decode the message. [After Mattila]

Acronym for secure telephone. See STU.

The portion of a transmission facility, including terminating points, between (a) a terminal network element (NE) and a regenerator (for example, a central office/remote terminal and customer location equipment such as a DTE) or (b) two regenerators. A terminating point is the point after signal regeneration at which performance monitoring is or may be done. [After T1.105-1988]

The boundary that separates a network section from the adjacent circuit section, or separates an access circuit section from the adjacent DTE (data terminal equipment). Synonym boundary.

(J0), a single byte or a sequence of bytes, used to transmit a unique message so that the receiving terminal in a section can verify it is connected to the intended transmitter.

A predetermined, addressable angular part of a track or band on a magnetic drum or magnetic disk.

A copy-protection technique for copy protection that determines whether a diskette is an unauthorized copy by checking whether sectors are positioned properly from track to track. [2382-pt.8]

In magnetic or optical disk storage media, the division of tracks into a specified number of segments, for the purpose of organizing the data stored thereon.

Telecommunications deriving security through use of type 1 products and/or protected distribution systems. [INFOSEC-99]

[The] specification for a secure hash algorithm that can generate a condensed message representation called a message digest. [INFOSEC-99]

Resident software controlling hardware and other software functions in an information system (IS) to provide a level of protection or security appropriate to the classification, sensitivity, and/or criticality of the data and resources it manages. [INFOSEC-99]

[The] condition in which no subject can access any object in an unauthorized manner. [INFOSEC-99]

[A] Subsystem containing its own implementation of the reference monitor concept for those resources it controls. Secure subsystem must depend on other controls and the base operating system for the control of subjects and the more primitive system objects. [INFOSEC-99]

See STU.

1. In transmission security, see secure communications.
2. In spread-spectrum systems, the transmission of binary coded sequences that represent information that can be recovered only by persons or systems that have the proper key for the spread-spectrum code-sequence generator, i.e., have a synchronized generator that is identical to that used for transmission. [From Weik '89]

See SECORD.

1. A condition that results from the establishment and maintenance of protective measures that ensure a state of inviolability from hostile acts or influences.
2. With respect to classified matter, the condition that prevents unauthorized persons from having access to official information that is safeguarded in the interests of national security.
3. Measures taken by a military unit, an activity… (Read More →)

A human authority which establishes a security policy and identifies the entities to which the policy applies [ECMA138].

1. An authority (a person or group of people) responsible for implementing the security policy for a security domain [ECMATR46].
2. An authority (a person or a group of people) responsible for implementing the security policy for a security domain [POSIX.6].

A security-related event that has been identified by a security policy as a potential breach of security. [T1.233-1993]

A high level description of the structure of a system, with security functions assigned to components within this structure [CESG].

1. Information, other than cryptographic keys, that is needed to establish and describe the protection mechanisms that secure the communications between two entities. [After X9.41]
2. A security attribute is a piece of security information which is associated with an entity in a distributed system [ECMA138].
3. Attributes associated with processes and files and used to determine access rights of… (Read More →)

A general term covering both privilege attributes and control attributes. The use of security attributes is defined by a security policy [ECMATR46].

1. Of data processing operations, an independent review and examination of system records and activities to (a) determine the adequacy of system controls, (b) ensure compliance with established security policy and operational procedures, (c) detect breaches in security, and (d) recommend any indicated changes in any of the foregoing.
2. An independent review and examination of system records and activities… (Read More →)

A message generated following the occurrence of an auditable security-related event [10181-7].

A single record in a security audit trail corresponding to a single security-related event [10181-7].

1. Set of records that collectively provide documentary evidence of processing used to aid in tracing from original transactions forward to related records and reports, and/or backwards from records and reports to their component source transactions. [TCSEC].
2. Data collected and potentially used to facilitate a security audit [7498-2].

An individual or a process allowed to have access to the security audit trail and to build audit reports [10181-7].

A nonhierarchical grouping of sensitive information used to control access to data more finely than with hierarchical security classification alone. [2382-pt.8]

A set of security relevant data which is protected by integrity and data origin authentication from an issuing security authority, and includes an indication of a time period of validity [10181-1].
Note: All certificates are deemed to be security certificates (see the relevant definitions in 7498-2). The term "security certificate" is adopted in order to avoid terminology conflicts with [X.509… (Read More →)

The combination of classification, categories and caveats associated with an object [CESG]. Example: "SECRET CORPORATE UK EYES A"
Note: Used only in the context of, and at the granularity of, a system's ability to distinguish between security classes. See also: Label, Lattice, Single Class, Multi-class.

1. Of information, the process of determining and designating the specific degree of protection against disclosure the information requires.
2. The level (degree) of protection so determined. [After 2382-pt.8]
Note: Examples of security classifications are: "top secret," "secret," and "confidential. "
3. Synonym security label.

1. The formal authorization by the Departmental Security Officer for an individual to have access to classified information, following appropriate vetting [CESG].
2. An attribute of a subject that specifies the security classes of objects for which access rights may be granted [CESG] See also: Lattice

1. An area of responsibility for the security of a system as defined in a System Security policy.
Note: The terms Global Security Environment (GSE), Local Security Environment (LSE) and Electronic Security Environment (ESE) are used to categorize security domains [CESG].
2. A bounded group of security objects and security subjects to which applies a single security policy executed by… (Read More →)

That which directly contributes to satisfying the security objectives of the Target of Evaluation [ITSEC].

An individual or process allowed to specify and manage the events which may generate a security message and to establish the action(s) to be taken for each security message type [10181-7]

The mechanism for conveying, or the conveyance of, security-related information between two entities. [After X9.41]

A set of logically associated security functions as used in the security framework [ECMATR46].

The invocation of a function a security facility by another security facility [ECMATR46].

[An] Assessment, usually performed on information system (IS) hardware, to determine the security properties of a device when hardware fault is encountered. [INFOSEC-99]

Report prepared by a CLEF and initially distributed to the Certification Body (CB). It describes situations whereby the Security policy of the Target of Evaluation (TOE) may be violated [CESG]. See also: Evaluation Observation Repor

1. In communications security, the hardware, firmware, or software used to prevent access to specified data by unauthorized persons or systems, such as by preventing transmission, preventing forwarding messages over unprotected lines or circuits, or requiring special codes for access to read-only files. [From Weik '89]
2. [An] Information-system (IS) -trusted subsystem that enforces security policy on the data that… (Read More →)

[An] Error of commission or omission in an information system (IS) that may allow protection mechanisms to be bypassed. [INFOSEC-99]

A discrete aspect of the performance of a system by which it enforces security automatically on behalf of the System Manager and /or system users [CESG].
Note: [1] Access control, authentication, accounting and audit are defined as major security functions which can be broken down into "functional elements". [2] The term is normally used at the requirements stage of a… (Read More →)

Common aspects of security policies necessary in order for interactions to take place between domains [10181-1]. .

1. In computer and communications security , the central part of a computer or communications system hardware, firmware, and software that implements the basic security procedures for controlling access to system resources.
2. A self-contained usually small collection of key security-related statements that (a) works as apart of an operating system to prevent unauthorized access to, or use of, the… (Read More →)

1. Information representing the sensitivity of a subject or object, such as its hierarchical classification ("confidential," "secret," "top secret") together with any applicable nonhierarchical security categories (e.g., sensitive compartmented information, critical nuclear weapon design information). [INFOSEC-99] Synonym security classification.
2. The marking bound to a resource (which may be a data unit) that names or designates the security attributes of… (Read More →)

1. The combination of a hierarchical security classification and a set of security categories that represents the sensitivity of an object or the security clearance of a subject. [2382-pt.8]
2. The combination of hierarchical classification and a set of non- hierarchical categories that represent the sensitivity of information [TCSEC].

The time over which cryptographically protected data or other security processes have value. [After X9.67]

In network management, the set of functions (a) that protects telecommunications networks and systems from unauthorized access by persons, acts, or influences and (b) that includes many subfunctions, such as creating, deleting, and controlling security services and mechanisms; distributing security-relevant information; reporting security-relevant events; controlling the distribution of cryptographic keying material; and authorizing subscriber access, rights, and privileges.

A means by which a System Security Policy is enforced [CESG].
Note: A general term, covering technical, procedural and management aspects of security.

The logic or algorithm that implements a particular security enforcing or security relevant function in hardware and software [ITSEC].

A mathematical or conceptual representation for specifying and proving system security [CESG]. Examples: Non-interference model, Information Flow model, Bell-LaPadula model.

An entity in a passive role to which a security policy applies [ECMATR46].

1. A statement of intent to counter specified threats and/or satisfy specified organizational security policies or assumptions.
2. The contribution to security which a Target of Evaluation is intended to achieve[ITSEC].

Documentation specifying the procedures that are to be carried out by system users (including the System Administrator and operators) to uphold all aspects of security devolved to the System Manager by the Departmental Security officer in the System Security Policy. Also abbreviated to SECOPS and SOPs [CESG]. See also: System Security Officer.

All components/devices of an information system (IS) to be accredited. Separately accredited components generally are not included within the perimeter. [INFOSEC-99]

1. The overall principles, regulations, requirements, and/or procedures which govern security as expressed by a responsible security authority: Examples: National security policy, Departmental security policy.
Note: Responsibility for security may be delegated by Departmental Security Officers to System Managers in accordance with a System Security Policy [CESG].
2. A set of rules that specify the procedures and mechanisms required to… (Read More →)

1. An informal presentation of a formal security policy model [POSIX.6].
2. An informal presentation of a formal security policy model [TCSEC].
3. A logically precise distillation of all or part of a System Electronic Information Security Policy, developed to avoid ambiguities and inconsistencies and to form a sound basis for subsequent stages of the development of a system [CESG].… (Read More →)

[The] highest and lowest security levels that are permitted in or on an information system (IS), system component, subsystem, or network. [INFOSEC-99]

That which is not security enforcing, but must function correctly for the Target of Evaluation to enforce security [ITSEC].

Any event that attempts to change the security state of the system, (e.g., change discretionary access controls, change the security level of the subject, change user password, etc. ). Also, any event that attempts to violate the security policy of the system, (e.g., too many attempts to login, attempts to violate the mandatory access control limits of a device, attempts… (Read More →)

The statement by the Departmental Security Officer (DSO) of the minimum standards to be met by a specific system and particular threats which are to be countered [CESG].
Note: A Security requirement should be stated in response to an Initial System Security Policy and should then be incorporated in the System Security policy. It should include a statement of the… (Read More →)

Protective measures and controls prescribed to meet the security requirements specified for an information system (IS). Safeguards may include security features, management constraints, personnel security, and security of physical structures, areas, and devices. [INFOSEC-99]

1. A set of operations designed to support some aspect of security in a distributed system [ECMA138].
2. A service, provided by a layer of communicating open systems, which ensures adequate security of the systems or of data transfers [7498-2].

Detailed description of the safeguards required to protect an information system (IS). [INFOSEC-99]

1. A proper subset of a security domain's entities which are subject to a security policy which possesses the following properties:
1. it includes all of the rules of the super-domain's policy where they apply;
2. additional rules are defined for the sub-domain policy action types where permitted by the policy of the super- domain;
3. it is administered by… (Read More →)

An entity in an active role to which a security policy applies [ECMATR46].

1. A set of security functional and assurance requirements and specifications to be used as the basis for evaluation of an identified product or system.
2. A specification of the security required of a Target of Evaluation, used as a baseline for evaluation. The security target will specify the security enforcing functions of the Target of Evaluation. It will also… (Read More →)

Examination and analysis of the safeguards required to protect an information system (IS), as they have been applied in an operational environment, to determine the security posture of that system. [INFOSEC-99]

1. [The] process to determine that an information system (IS) protects data and maintains functionality as intended. [INFOSEC-99]
2. A process used to determine that the security features of a system are implemented as designed and that they are adequate for a proposed application environment. This process includes hands- on functional testing, penetration testing, and verification [TCSEC]. See also: Functional… (Read More →)

A set of security relevant data which is protected by integrity and data origin authentication from a source which is not considered a security authority [10181-1].

Acronym for self-electro-optic effect device. An optically bistable device used for photonic switching.
Note: A self-electro-optic device consists of multiple elements, biased by an external voltage which creates an external field that shifts the wavelength of the onset of absorption, thus varying the intensity of the transmitted light.

A random value, either from a random-number generator or a pseudorandom number generator, used as an input to a hash function, whose output is then used as an input parameter into a key-generation algorithm. [After X9.31]

[In INFOSEC, an] initial key, used to start an updating or key generation process. [INFOSEC-99]

To position selectively the access mechanism of a direct access [storage] device.

The time required for the access arm of a direct-access storage device to be positioned on the appropriate track. Synonym positioning time.

In a distributed queue dual bus (DQDB) network, a protocol data unit (PDU) that (a) consists of 52 octets transferred between DQDB-layer peer entities as the information payload of a slot, (b) contains a header of 4 octets and a payload of 48 octets, and (c) is either a pre-arbitrated segment or a queued arbitrated segment.

An encoding law in which an approximation to a curve defined by a smooth encoding law is obtained by a number of linear segments. Synonym piecewise linear encoding law.

Synonym privacy.

The temporary dedication of various parts of a communications system to a specific use, usually in response to a user request for service.
Note: The parts seized may be automatically connected, such as by direct distance dialing (DDD), or may require operator intervention.

In telephone systems, a signal used by the calling end of a trunk or line to indicate a request for service.
Note: A seizure signal also locks out the trunk or line to other demands for service.

Acronym for selective calling. Calling from one station in which call identification is sent to signal automatically one or more remote stations and to establish links among them.
Note 1: Selective calling may be used to un-mute the speakers at designated stations or to initiate a handshake for link establishment.
Note 2: Selective calling is specified in ITU-R Recommendations for… (Read More →)

For a particular message path, any intermediate network between a branch point and a subsequent branch point or convergence point is a selected network. [T1.118-1992]

Synonym decision instant.

See selcall.

Synonym maximal-ratio combiner.

Fading in which the components of the received radio signal fluctuate independently.

The protection of specific fields within a message which is to be transmitted [7498-2].

See electronic warfare.

In a party line, ringing only the desired user instrument.
Note: Without selective ringing, all the instruments on the party line will ring at the same time, selection being made by the number of rings.

An element of the emergency services network that provides routing information for emergency calls based on geographic information. It provides the association of an originating (or calling) telephone number to a PSAP that is the terminating point that handles emergency calls for the area that contains the origination number.

A measure of the ability of a receiver to discriminate between a wanted signal on one frequency and unwanted signals on other frequencies.

1. A procedure in which a transmitting station , i.e., a calling station, establishes its own validity without the participation of the receiving station, i.e., the called station.
Note: The calling station establishes its own authenticity and the called station is not required to challenge the calling station. Self- authentication is usually used only when one- time authentication systems are… (Read More →)

A block in which a bit pattern or a flag identifies the beginning or end of a block.

See SEED.

In the optical regime, the property of an element (rod or slab of material) that (a) has a refractive index gradient that is a defined function of the radial distance from its optical axis, and (b) by virtue of which gradient, is capable of focusing light in a manner after that of a conventional simple lens.
Note 1: For example,… (Read More →)

In computer programming, a partial computer address that uses the base address of the computer program, in which it appears, as the ellipsed component of the partial address.
Note 1: A program that uses self-relative addresses will be portable, in that all related programs and subroutines can be moved, together, to a different computer or subdirectory, and all components will… (Read More →)

A code in which the symbol stream formed by a portion of one code word, or by the overlapped portion of any two adjacent code words, is not a valid code word.
Note 1: A self-synchronizing code permits the proper framing of transmitted code words provided that no uncorrected errors occur in the symbol stream.
Note 2: External synchronization is… (Read More →)

A circuit that uses the data it is retransmitting to perform tests on itself to ensure that it is transmitting properly, i.e., to ensure that all circuit components are functioning properly. [After Weik '96]

A connection established via a service order or via network management. [T1.627-1993]

A machine-aided command and control system in which human intervention is required in varying degrees to operate the system.

1. In telephone systems, a switching system in which telephone operators receive call instructions orally from users and complete them by automatic equipment.
2. At tape-relay intermediate stations, the manual routing or rerouting of taped messages without rekeying them.

Synonym injection laser diode.

1. A method which is simplex operation at one end of the circuit and duplex operation at the other. RR Footnote: In general, duplex operation and semiduplex operation require two frequencies in radiocommunication; simplex operation may use either one or two. [NTIA] [RR]
2. Operation of a communications network in which a base station operates in a duplex mode with… (Read More →)

See sending loudness rating. [T1.508-1998]

A device that accepts address information from a register or routing information from a translator, and then transmits the proper routing information to a trunk or to local equipment.
Note: Sender and register functions are often combined in a single unit.

The ratio in dB of the sound pressure produced by a speaker to the voltage produced by a telephone and loop as defined by ITU-T Recommendation P.7
9. [T1.255-1997]

In teletypewriter (TTY) systems, interference, in a given channel, caused by transmissions from one or more adjacent TTY channels transmitting from the end at which the crossfire, i.e., interference, is measured.

1. Information, the loss, misuse, or unauthorized access to or modification of, which could adversely affect the national interest or the conduct of federal programs, or the privacy to which individuals are entitled under 5 U. S. C. Section 552a (the Privacy Act), but that has not been specifically authorized under criteria established by an Executive Order or an Act… (Read More →)

1. In an electronic device, e.g., a communications system receiver, or detection device, e.g., PIN diode, the minimum input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria.
Note 1: The signal input may be expressed as power in dBm or as field strength in microvolts per meter, with input network impedance… (Read More →)

1. Information representing elements of the security label(s) of a subject and an object. Sensitivity labels are used by the trusted computing base (TCB) as the basis for mandatory access control decisions. [INFOSEC-99]
2. A piece of information that represents the security level of an object and that describes the sensitivity (e.g., classification) of the data in the object. Sensitivity… (Read More →)

A device that responds to a physical stimulus, such as thermal energy, electromagnetic energy, acoustic energy, pressure, magnetism, or motion, by producing a signal, usually electrical.

See flag.

Signaling in which the whole or a part of one or more channels in a multichannel system is used to provide for supervisory and control signals for the message traffic channels.
Note: The same channels, such as frequency bands or time slots, that are used for signaling are not used for message traffic.

The concept of keeping information of different security classes apart in a system [CESG].
Note: Separation may be implemented by temporal, physical, logical or cryptographic techniques

In secure communications, dividing responsibility for sensitive information so that no individual acting alone can compromise the security of the data processing system. [2382-pt.8]

The process by which telecommunication property costs, revenues, expenses, taxes, and reserves are apportioned among the operations. [47 CFR Pt.36-A]

A byte composed of seven binary elements. Synonym seven-bit byte.

An arrangement of items according to a specified set of rules, for example, items arranged alphabetically, numerically, or chronologically.

In a packet, a field of the packet header that is used by the terminating endpoint to determine if the packets arrive in sequence. [T1.509-1995]

Synonym serial access.

A device that has at least one output channel and one or more input channels, all characterized by discrete states, such that the state of each output channel is determined by the previous states of the input channels.

Synonym serial transmission.

1. Pertaining to a process in which all events occur one after the other; for example, the serial transmission of the bits of a character according to the ITU-T V.25 protocol.
2. Pertaining to the sequential or consecutive occurrence of two or more related activities in a single device or channel.
3. Pertaining to the sequential processing of the individual… (Read More →)

1. Pertaining to the sequential or consecutive transmission of data into or out of a device, such as a computer, transmission line, or storage device.
2. A process by which data are obtained from a storage device or entered into a storage device in such a way that the process depends on the location of those data and on a… (Read More →)

1. A computer that has a single arithmetic and logic unit.
2. A computer, some specified characteristic of which is serial; for example, a computer than manipulates all bits of a word serially.

A port through which data are passed serially, i.e., one bit at a time, and that requires only one input channel to handle a set of bits, e.g., all the bits of a byte.

The sequential transmission of the signal elements of a group representing a character or other entity of data.
Note: The characters are transmitted in a sequence over a single line, rather than simultaneously over two or more lines, as in parallel transmission. The sequential elements may be transmitted with or without interruption. Synonym sequential transmission.

Conversion of a stream of data elements received in time sequence, i.e., one at a time, into a data stream consisting of multiple data elements transmitted simultaneously.

See parallel-to-serial conversion.

A three-port waveguide junction that has an equivalent circuit in which the impedance of the branch waveguide is predominantly in series with the impedance of the main waveguide at the junction.

A network device that provides service to the network users by managing shared resources.
Note 1: The term is often used in the context of a client-server architecture for a local area network (LAN).
Note 2: Examples are a printer server and a file server.

An application process that implements all or part of the functionality defined by a service definition [ECMATR46].

1. In Service Oriented Networks, the two basic uses of service are:
a)Something of value being provided to and consumed by end-users of communications networks. It may be a specific service, such as Verizon FIOS IPTV Premier or Acme Restaurant Finder, or it may be general, such as VoIP telephony service or emergency services.
b)A function that is performed by… (Read More →)

In personal communications service (PCS), the ability for the network to provide user access to features and to accept user service requests specifying the type of bearer services or supplementary service that the users want to receive from the PCS network.

A non-geographic NPA or ERC used for the purpose of providing access to a specific type of service.

1. A physical point at which a circuit may be accessed.
2. In an Open Systems Interconnection (OSI) layer, a point at which a designated service may be obtained.

A parameter value consistent with minimum service objectives that are necessary to support high-speed modems. When any parameter values exceeds the SAL, voiceband data performance may be adversely affected, depending on the performance of the remainder of the connection. [T1.506-1989]

Of a virtual connection section, the long-term percentage of scheduled service time during which that section is available. [After T1.504-1989]

A system overhead bit used for providing a network service, such as a request for a repetition or for a numbering sequence.
Note: A service bit is not a check bit.

Synonym orderwire circuit.

See class of service.

A two-digit code used in the EC-to-IC (exchange carrier-to-interexchange carrier) facility/service selective signaling protocol and the IC-to-EC facility/service selective signaling protocol that identifies the type of service requested. [T1.104-1991]

Service composition imparts to the user the experience of one seamless, composite service instead of separate services, by way of additional functionality that binds service enablers together.

A sharing of an active service among devices or networks. This can include various manipulations to share, extend, or prune membership in a multi-party service or multi-network connectivity that supports it. The concept of concurrence applies not only to a service, but also to sessions, application associations and to context.

The continuation of active service across devices, or access networks, or both from the user's point of view. For example, service continuity can apply to single services such as voice, or to composite services such as voice and video along with associated data exchange such as web browsing or instant messaging. Service continuity may be seamless and performed automatically. Alternatively,… (Read More →)

Direction of the functions or processes used to provide a specific telecommunications service. [T1.667-1999]

The real-time database systems in the Exchange Carrier network that contain routing instructions downloaded by the SMS/800 andimplements service control functions. such as:

Call control
Call state control function
Multimedia session control function

An entity designated to manage and administer Service Control Points (SCPs).

A similar service experience from the user's perspective provided across different provider networks, access technologies, and end devices, recognizing the limitations of different devices and technologies. Converged services can leverage shared application functions, across different access media, terminal types, and service providers. An example of service convergence would be email service delivered to a mobile terminal, a television, or a… (Read More →)

In layered systems, a set of data that is sent by a user of the services of a given layer, and is transmitted to a peer service user semantically unchanged.

In telephony, any of a number of special functions that may be specified initially, or added to, the user's basic service.
Note: Modern telephone switches are capable of providing a wide variety of service features, such as call forwarding and call waiting.

The information that uniquely identifies an NS/EP telecommunications service to the service vendor and the service user.

Not necessarily specific to one service. [T1.667-1999]

The information that is necessary for the ITF Device to locate and access the content.

Imparts to the user the experience of one seamless, composite service instead of separate services, by way of additional functionality that binds them together.
For example, IPTV and VoIP service where the viewer's IPTV screen displays “Mom“ over the current program and the sound mutes while the incoming call from Mom is delivered to the target device (e.g., house phone).… (Read More →)

The degree to which a service is provided without excessive impairment, once obtained. [NATO]

Imparts to the user the experience of one seamless, composite service instead of separate services, by way of additional functionality that binds them together.
For example, IPTV and VoIP service where the viewer's IPTV screen displays “Mom“ over the current program and the sound mutes while the incoming call from Mom is delivered to the target device (e.g., house phone).… (Read More →)

A sequence of processes/functions used to provide a specific service. [T1.667-1999]

Function to check the layer 4-7 functionality of any device in the home.

The entity equivalent to the work station function between network operators and/or subscribers and network service management functional entities. [T1.667-1999]

An entity comprised of the Regional Bell Operating Company's (RBOCs) who were ordered by the FCC to administer the SMS/800 at the advent of portability (May 1993).

A physical entity that contains the service control function, service data function, specialized resource function and service switching/call control functions. The SSF/CCF is closely coupled to the SCF within the SN and is not accessible by other SCFs. [T1.667-1999]

Service Orchestration is a mechanism for doing dynamic service composition. In a service oriented architecture, a service orchestration tool (e. g. Web Services orchestration) can be used to create a combined service or integrated service (offering a combined or integrated user experience), by orchestrating the invocation of individual services, in response to user requests, network events or other inputs. A… (Read More →)

The state of a service when (a) a network failure impairs or prevents the initiation of new requests for the service, (b) continued use of the service is impaired or not possible, or (c) certain service parameters fall outside prescribed limits. [After T
1. Rpt38-1994]

A service package represents a grouping of one or more TV channels. Service packages can be used for multiple purposes, such as being a unit of subscription, policy download in RACF, etc. Each service package is assigned an identity. The actual grouping of channels within a service package is under control of the IPTV of the service provider. A TV… (Read More →)

The probability of obtaining a specified (or higher) grade of service during a given period of time.

Synonym UPT service profile.

Synonym UPT service profile management.

Synonym utility program.

1. An organization that provides services for content providers and for users of a communications network.
Note: The services may include access to the communications network, content hosting, server of a private message handling system, news server, etc. [After 2382-pt.35]
2. A company, organization, administration, business, etc. , that sells, administers, maintains, charges for, etc. , the service. The service… (Read More →)

Service Provider discovery is the process by which an ITF becomes aware of the available IPTV Service Provider(s) and learns the means for attaching to a Service Provider over a secure managed network.

An entity designated to manage and administer the texting and other multi-media services portion of Toll-Free Numbers within the Texting & Smart Services (TSS) Registry.

Synonym utility program.

Signals that enable data systems equipment to function correctly, and possibly to provide ancillary facilities. Synonym housekeeping signals.

An entity that contracts for services offered by service providers. [T1.667-1999]

A physical entity that contains the service control function, service data function and the service switching/call control functions. [T1.667-1999]

The set of processes that provide for interaction between a call control function and a service control function. [T1.667-1999]

A physical entity that implements a service switching function. [T1.667-1999]

The last point of service rendered by a commercial carrier under applicable tariffs.
Note 1: The service termination point is usually on the customer premises.
Note 2: The customer is responsible for equipment and operation from the service termination point to user end instruments.
Note 3: The service termination point usually corresponds to the demarcation point.

The term used to describe service continuity, which is supported from the network point of view.

An individual or organization, including a service vendor, that is provided a telecommunications service for which a priority level has been requested or assigned.

is a number from one to five where one has the highest priority for ETS (Legacy GETS, WPS, or NGN-PS) services and five has the lowest priority for ETS (Legacy GETS, WPS, or NGN-PS) services. The Service User’s priority level is assigned to a Service User.

The term number portability means the ability of users of telecommunications services to retain, at the same location, existing telecommunications numbers without impairment of quality, reliability, or convenience when switching from one telecommunications carrier to another (47 CFR§
5
2. 21 (m)).

Services Discovery is the process by which an ITF receives the necessary data elements which enable the ITF to access the available IPTV Services.

Information that identifies the local serving area where the network provider operates. [After T1.667-1999]

The simultaneous participation of a plurality of devices or networks in supporting a session as well as merging two or more existing sessions into a single session.

An encryption key that provides privacy during a call and may be changed dynamically by the system. [T
1. Rpt22-1993]

See Open Systems Interconnection--Reference Model.

1. A finite or infinite number of objects, entities, or concepts, that have a given property or properties in common.
2. To configure all or part of a device into a specified state.

Abbreviation for secure electronic transaction.

Referring to an auxiliary device that usually rests on top of or adjacent to a television receiver and that is used in direct analog or digital satellite transmissions and digital television to be viewed on analog television; a set-top device may convert cable TV or Web signals to a form or format that allows end-user channel selection or interaction via… (Read More →)

When used by a telco, this typically describes a box that translates the IPTV services running across the home netowork and makes them displayable to the TV (includes the video decode function, EPG function, DRM, games, ITV, personalization, etc. ). See also, set-top, set-top converter.

Synonym septet.

A personal telephone service that allows individuals to receive, via a single number, telephone calls in various locations (e.g., home, office, or car) from call originators using the same common carrier.

A one-second period that contains >30% errored blocks or at least one severely disturbed period. A severely disturbed period occurs when, over a period of time equivalent to 1 ms, all the contiguous blocks are affected by a high bit error density.
Note: A period of loss of signal or a bit error density of >10-2 is considered a period… (Read More →)

1. A specified period of time, during which bits are transferred from a source to a destination, where 30% of the blocks received are errored, or at least one severely disturbed period occurred. A severely disturbed period occurs when, over a period of time equivalent to four contiguous blocks or 1 ms, whichever is larger, all the contiguous blocks are… (Read More →)

Synonym hexadecimal.

A byte composed of six binary elements. Synonym six-bit byte.

Abbreviation for single-frequency. See single-frequency signaling.

Abbreviation for standard frequency and time signal. See standard time and frequency signal service.

Signaling Gateway

Signaling Gateway Function

Abbreviation for Standard Generalized Mark-up Language. A file format for storage of text and graphics files.

Serving GPRS Support Node

In secure systems, a permutation of the bits in a byte or other data unit, which permutation is used to increase redundancy during the signature process. [After X9.31-1]

1. The attenuation caused to a radio signal by obstructions in the propagation path.
2. In a reflector antenna, the relative reduction in the effective aperture of the antenna caused by the masking effect of other antenna parts, such as a feed horn or a secondary reflector, which parts obstruct the radiation path.

The unit of information derived from the occurrence of one of two equiprobable, mutually exclusive, and exhaustive events.
Note: A bit may, with perfect formatting and source coding, contain 1 Sh of information. However, the information content of a bit is usually be less than 1 Sh.

A statement defining the theoretical maximum rate at which error-free digits can be transmitted over a bandwidth-limited channel in the presence of noise, usually expressed in the form C = W log2(1 + S/N), where C is the channel capacity in bits per second, W is the bandwidth in hertz, and S/N is the signal-to-noise ratio.
Note: Error-correction codes can… (Read More →)

A network inserted in a circuit for the purpose of improving or modifying the waveform of signals.

A service link connection that can be used by any service customer (SC) in a predefined set of SCs on a first-come, first-service-basis; that is, during a specific time period, only one SC can use the service link connection, and the right to use the service link connection is assigned on a first-come, first-served basis. [After T1.263-1998]

Software available for downloading from public networks and bulletin board systems, usually at little cost.
Note: At the end of a trial period, users are asked to pay the software developer a small amount for use of the software. [After Bahorsky]

The informal, subjective evaluation of detail in the clarity or resolution seen in an image.
Note: Often sharpness and resolution are assumed to be directly related, because images possessed of greater sharpness are assumed to have greater resolution. An increase in subjective sharpness is usually reported when objects are more clearly delineated from each other and from background having hard,… (Read More →)

Super Head End

Of a communications or power cable, the outer covering or coverings of tough material, often plastic, that is resistant to environmental hazards such as abrasion, liquid intrusion, solar radiation, etc. , and is used to protect cable component(s) such as optical fibers or metallic conductors that transport the signal or power.
Note: There may be more than one sheath surrounding… (Read More →)

The actual length of cable in route kilometers. [47 CFR Pt.36-A]

The actual length of cable in route miles. [47CFR]

In a computer environment, an operating system command interpreter, i.e., a software utility that reads an input specifying an operation, and that may perform, direct, or control the specified operation.
Note 1: For example, a shell may permit a user to switch among application programs without terminating any of them.
Note 2: A shell may take its input from either… (Read More →)

Abbreviation for super high frequency. See electromagnetic spectrum.

1. A housing, screen, sheath, or cover that substantially reduces the coupling of electric, magnetic, or electromagnetic fields into or out of circuits or transmission lines.
2. A protective cover that prevents the accidental contact of objects or persons with parts or components operating at hazardous voltage levels.

[A] room or container designed to attenuate electromagnetic radiation. [INFOSEC-99]

A 2-wire transmission line surrounded by a sheath of conductive material that protects it from the effects of external fields and confines fields produced within the line.

A transmission line composed of a twisted 2-wire metallic transmission line surrounded by a sheath of conductive material that protects it from the effects of external fields and confines fields produced within the line.

See shield.

The factor that expresses the attenuation caused by scattering, e.g., of radiant or acoustic energy, during its passage through a medium.
Note: The scattering coefficient is usually expressed in units of reciprocal distance.

1. The movement of some or all of the characters or bits of a word by the same number of character or bit positions in the direction of a specified end of a word.
2. In radar, the ability to move the origin of a radial display away from the center of the cathode ray tube.

A storage device, usually in a central processing unit (CPU), in which device a serially ordered set of data may be moved, as a unit, into a discrete number of storage locations.
Note 1: Shift registers may be configured so that the stored data may be moved in more than one direction.
Note 2: Shift registers may be configured so… (Read More →)

A mobile Earth station in the maritime mobile-satellite service located on board ship. [NTIA] [RR]

A mobile station in the maritime mobile service located on board a vessel which is not permanently moored, other than a survival craft station. [NTIA] [RR]

A ship's transmitter to be used exclusively on a distress frequency for distress, urgency or safety purposes. [NTIA] [RR]

Synonym impulse excitation.

Synonym response spectrum.

In electronic commerce (also called "e-commerce"), an application allowing users of a commercial Web site to select products from the screen display as they browse, and then to securely pay for all of those selected products in one secure transaction. [After Bahorsky]

The term "Short Circuit Test Line" denotes an arrangement in an end office which provides for an ac short circuit termination of a trunk or line by means of a capacitor of at least four microfarads.

A general term applied to message toll traffic between nearby points. In common usage, this term is ordinarily applied to message toll traffic between points less than 20 to 50 miles apart. [47CFR]

An event beginning with the occurrence of a bit error ratio (BER) of 10-2 or worse, continuously for each of three or more consecutive seconds, which can last up to 120 seconds. An SIE clears when 10 consecutive seconds pass in which none of them is an SES.
Note: The 10-2 BER continuously over each second implies that all sub-intervals,… (Read More →)

A store-and-forward service in telephony and data systems that allows the exchange of short text messages between end-user devices; the length of the message varies by language up to a maximum of 160 characters in the Latin alphabet. There are gateways from e-mail and Web to SMS, and from SMS to e-mail. The term “SMS” is sometimes also used to… (Read More →)

In optical communication, optical radiation having a wavelength less than approximately 1 m.

In radio communications, pertaining to the band of frequencies approximately between 3 MHz and 30 MHz.
Note: "Shortwave" is not a term officially recognized by the international community.

The noise caused by random fluctuations in the motion of charge carriers in a conductor.
Note: There is often a minor inconsistency in referring to shot noise in an optical system: many authors refer to shot noise loosely when speaking of the mean square shot noise current (amperes2) rather than noise power (watts).

Abbreviation for International System of Units.

1. service access code,
2. special area code.

Either of the two circuits used to derive a phantom circuit.

Any way in which one representation differs from previous representations, but which is not revealed by the verification methods adopted, and can lead to failure to satisfy the security requirements [CESG].

In a directional antenna radiation pattern, a lobe in any direction other than that of the main lobe.

In amplitude modulation (AM), a band of frequencies higher than or lower than the carrier frequency, containing energy as a result of the modulation process.
Note: Amplitude modulation results in two sidebands. The frequencies above the carrier frequency constitute what is referred to as the "upper sideband"; those below the carrier frequency, constitute the "lower sideband. " In conventional AM… (Read More →)

See single-sideband transmission.

The sound of the speaker's own voice (and background noise) as heard in the speaker's telephone receiver.
Note: Sidetone volume is usually suppressed relative to the transmitted volume. Synonym telephone sidetone.

1. Abbreviation for special interest group.
1. Within a given technical discipline or area of knowledge, a circle of individuals or organizations having an intensified interest in a narrower facet of the general area.
2. In networking, particularly involving Internet applications, a group of individuals or organizations that sponsor, e.g., IRC channels, mailing lists, or Web sites for the purpose… (Read More →)

Acronym for signals intelligence.

1. Detectable transmitted energy that can be used to carry information.
2. A time-dependent variation of a characteristic of a physical phenomenon, used to convey information.
3. As applied to electronics, any transmitted electrical impulse. [JP1]
4. Operationally, a type of message, the text of which consists of one or more letters, words, characters, signal flags, visual displays, or special… (Read More →)

A combination of signal communication facilities operated by the Army in the field and consisting of a communications center, telephone switching central and appropriate means of signal communications. [JP1]

1. In analog (usually audio) systems, reduction of the dynamic range of a signal by controlling it as a function of the inverse relationship of its instantaneous value relative to a specified reference level.
Note 1: Signal compression is usually expressed in dB.
Note 2: Instantaneous values of the input signal that are low, relative to the reference level, are… (Read More →)

In facsimile, the ratio of the level of the white signal to the level of the black signal.
Note: Signal contrast is usually expressed in dB.

Synonym modem.

1. A measure of the difference between a given signal and a reference signal.
Note: For analog signals, the signal distance is the root mean square difference between the given signal and a reference signal over a symbol period.
2. Synonym Hamming distance.

See distortion.

In an otherwise essentially flat-topped rectangular pulse, distortion characterized by a decline of the pulse top.

A multifrequency (MF) or dual-tone multifrequency (DTMF) signal timing interval during which the signal is being transmitted. For MF signals the signal duration interval begins when the last tone of the MF tone pair exceeds 90% of its steady-state value and ends when either tone of the MF tone pair falls below 90% of its respective steady-state value. For DTMF… (Read More →)

A part of a signal, distinguished by its nature, magnitude, duration, transition, or relative position.
Note: Examples of signal elements include signal transitions, significant conditions, significant instants, and binary digits (bits).

Restoration of the dynamic range of a compressed signal.

See frequency shift.

See signals intelligence.

In a communications system, the signal power or intensity at a specified point and with respect to a specified reference level, e.g., 1 mW.

In communications systems, a message, i.e., an assembly of signaling information, that (a) includes associated message alignment and service indications, (b) pertains to a call, and (c) is transferred via the message transfer part.

The processing--such as detection, shaping, converting, coding, and time positioning--of signals, that results in their transformation into other forms, such as other waveshapes, power levels, and coding arrangements.

1. The ratio of (a) the signal-to-noise ratio of a processed signal to (b) the signal-to-noise ratio of the unprocessed signal.
Note: Signal processing gain is usually expressed in dB.
2. In a spread-spectrum communications system, the signal gain, signal-to-noise ratio, signal shape, or other signal improvement obtained by coherent band spreading, remapping, and reconstitution of the desired signal.

The portion of a facility grounding system that (a) provides reference planes, such as ground-return circuits, for all of the signal paths in the facility and (b) is isolated from other circuits, especially isolated from circuits that carry fault, lightning discharge, and power distribution currents.

Signal processing that restores a signal so that it conforms to its original characteristics.

The value of a particular characteristic of a signal at a chosen instant.

The process of obtaining a sequence of instantaneous values of a particular signal characteristic, usually at regular time intervals.

A generic term that includes both communications security and electronics security. [JP 1-02]

1. In a common-channel signaling network, a switch that provides for the transfer from one signaling link to another.
Note: In nonassociated common-channel signaling, the signal transfer point is not the point through which the call, which is associated with the signaling being switched, passes.
2. A packet switching device that performs a message routing function in a CCS network.… (Read More →)

1. In the modulation of a carrier, a change from one significant condition to another.
Note 1: Examples of signal transitions are a change from one electrical current, voltage, or power level to another; a change from one optical power level to another; a phase shift; or a change from one frequency or wavelength to another.
Note 2: Signal transitions… (Read More →)

A group of bits forming a separately transferable entity used to convey information on a signaling link. [T1.226-1992]

The alignment that exists when flags are received at intervals that correspond to integral numbers of octets and that fall within certain upper and lower limits. [T1.110-1987]

A procedure by which the error rate of an active signaling link is measured on the basis of a count of correctly checking and erroneous signal units. [T1.110-1987]

Procedures used at Level 2 to ensure that message signal units are transported in sequence, without loss or duplication, over a particular signaling link. [T1.110-1987]

See SINAD.

At a given point in a communications system, the ratio of (a) the power of the desired signal plus the noise to (b) the power of the noise.
Note: The (S+N)/N ratio is usually expressed in dB.

A current-carrying return path from a load back to the signal source, i.e., the low side of the closed loop energy transfer circuit between a source-load pair.

The term "Signal-to-C-Notched Noise Ratio" denotes the ratio in dB of a test signal to the corresponding C-Notched Noise.

At a specified point in a circuit, the ratio of the power of the wanted signal to the power of the unwanted signal from another channel.
Note 1: The signals are adjusted in each channel so that they are of equal power at the zero transmission level point in their respective channels.
Note 2: The signal-to-crosstalk ratio is usually expressed… (Read More →)

The ratio of the amplitude of the desired signal to the amplitude of noise signals at a given point in time. [JP1]
Note 1: SNR is expressed as 20 times the logarithm of the amplitude ratio, or 10 times the logarithm of the power ratio.
Note 2: SNR is usually expressed in dB and in terms of peak values for… (Read More →)

The ratio given by Eb/N0, where Eb is the signal energy per bit and N0 is the noise energy per hertz of noise bandwidth.

1. The use of signals for controlling communications.
2. In a telecommunications network, the information exchange concerning the establishment and control of a connection and the management of the network, in contrast to user information transfer.
3. The sending of a signal from the transmitting end of a circuit to inform a user at the receiving end that a message… (Read More →)

A data channel in combination with its associated signaling terminal equipment. [T1.226-1992]

1. A component part of SS7 protocol that provides additional functions to the message transfer part (MTP) to provide for Connectionless and Connection Oriented network services to transfer signaling information between exchanges and specialized centers in telecommunication networks. The combination of the MTP and the SCCP is called Network Service part. [T1.235-1993]
2. The part of SS7 that provides additional… (Read More →)

A combination of two data channels operating together in a single signaling system. [T1.226-1992]

A signaling point to which a message is destined. [T1.226-1992]

1. A signaling point that can send or receive SS7 messages, and has no message transfer function. [T1.235-1993]
2. A signaling point with the ability to source or sink network service part user data and considered exclusively from the viewpoint of the source or sink. [T1.110-1987]

The bits of a message signal unit that carry information particular to a certain user transaction and always contain a label. [T1.110-1987] [T1.226-1992]

A transmission facility that consists of a signaling data link and its transfer control functions, used for reliable transfer of a signaling message. [After T1.236-1993]

The process of making a signaling link ready to carry signaling traffic.

An event that causes the unavailability of a signaling link, typically consisting in a "processor outage" condition at one end of that signaling link. [T1.110-1987] [T1.226-1992]

1. A field with certain signaling network management messages, which indicates the particular signaling link to which the message refers among those interconnecting the two involved signaling points.
2. A field in signaling link test message as well as in some signaling network management messages that indicates the particular signaling link, interconnecting the two involved signaling points, to which the… (Read More →)

The procedure by which a signaling link is taken out of service. [T1.110-1987]

An event that causes the unavailability of a signaling link, typically consisting of a failure in signaling terminal equipment or in the signaling data link. [T1.110-1987] [T1.226-1992]

A set of signaling links directly connecting two signaling points and having the same physical characteristic (bit rate, propagation delay, and the like). [T1.110-1987]

One of a group of functions that control and take actions when required to preserve integrity of locally connected signaling link sets. [T1.226-1992]

An event characterizing the completion of the initial alignment procedure on a signaling link following the removal of the previous causes of failure; in the absence of any other causes of its unavailability, the signaling link once again becomes available. [T1.226-1992]

A field of the routing label that is typically used by the message routing function to perform load sharing among different signaling links n, or link sets h. [T1.226-1992]

A field of the routing label that is typically used by the message routing function to perform load sharing among different signaling links or link sets. [T1.110-1987]

A set of signaling link(s) directly connecting two signaling points. [T1.110-1987]

1. An assembly of signaling information pertaining to a call that includes, but is not limited to, management transactions, that is transferred (between signaling points) as an entity. [T1.226-1992]
2. An assembly of signaling information that pertains to a call management transaction, and the like and that is transferred as an entity. [T1.110-1987]

At a given signaling point, the process that decides, for each incoming message, whether the signaling point is destination point or if it should act as signaling transfer point for that message, and accordingly, whether the message should be handed to (signaling) message distribution or to (signaling) message routing functions. [After T1.110-1987] [After T1.226-1992]

The process of determining upon receipt of a signaling message at its destination point, to which user part the signaling message is to be delivered. [T1.110-1987]

Functions that, at the actual transfer of a message, direct the message to the proper signaling link or user part. [T1.226-1992]
Note: The message handling functions include functions for message distribution, message discrimination, and message routing.

The signaling link or consecutive links connected in tandem that are used to convey a signaling message from an originating point to its destination point. [T1.110-1987] [T1.226-1992]

The process for selecting, for each signaling message to be sent, the signaling link to be used. [T1.110-1987]

A network used for signaling by one or more users and consisting of signaling points and connecting signaling links. [T1.110-1987] [T1.226-1992]

The functions that are performed by the message transfer part at level 3 and are common to, and independent of, the operation of individual signaling links. They include the signaling message handling functions and the signaling network management functions.
Note: The message handling functions include functions for message distribution, message discrimination, and message routing. [T1.110-1987][T1.226-1992]

Functions that control the current message routing and configuration of signaling network facilities based on predetermined data and current information about the status of the signaling network. [T1.226-1992]

A signaling point that is the source of a message. [T1.226-1992]

In a transmission system, a path used for system control, synchronization, checking, signaling, and service signals used in system management and operations rather than for the data, messages, or calls of the users.

A node in a signaling network that either originates and receives signaling messages, or transfers signaling messages from one signaling link to another, or both. [After T1.110-1987] [After T1.234-1993]

A binary code uniquely identifying a signaling point in a signaling network. This code is used, according to its position in the label either as destination point code or as originating point code. [T1.110-1987] [T1.226-1992]

See data signaling rate.

A predetermined path described by a succession of signaling points that may be traversed by signaling messages directly by a signaling point towards a specific destination point. [T1.110-1987]

A set of protocols that exchanges information between telecommunication systems and networks for establishing, maintaining, and terminating telephone calls within the PSTN.
Note: SS7 is a prerequisite for implementation of an Integrated Services Digital Network (ISDN). Signaling System No.7 is described in ITU-T Recommendations and ANSI American National Standards.

In TDM carrier systems, a time slot starting at a particular phase or instant in each frame and allocated to the transmission of signaling (supervisory and control) data.

Actions and procedures intended to limit signaling traffic at its source in the case when the signaling network is not capable of transferring all signaling traffic offered by the user parts, because of network failures or overload situations. [T1.110-1987] [T1.226-1992]

Functions that control, and when necessary, modify, routing information used by message routing information to control the transfer of signaling traffic in a manner that avoids irregularities in message flow. [T1.226-1992]

See signal transfer point.

See signal transition.

1. A category of intelligence comprising, either individually or in combination, all communications intelligence, electronics intelligence, and foreign instrumentation signals intelligence, however transmitted. [JP 1-02]
2. Intelligence derived from communications, electronics, and foreign instrumentation signals. [JP 1-02]

[A] generic term encompassing communications security and electronic security. [NIS]

The entity that generates a digital signature on data. [After X9.31]

In secure communications, an agreed entity (usually a third party) that issues signatory certificates to organizations participating in this authorization system. [After X9.45]

In encryption, a certificate, issued by a signatory authority, that identifies the authorized signatories of an organization. [After X9.45]

1. The complete set of signals, usually electromagnetic or acoustic, received from a source such as an infrared object, a radio or radar transmitter, an aircraft, or a ship.
Note: Signatures may consist of analog or digital signals, or both, and may be analyzed to indicate the nature of their source and assist in its recognition.
2. The attributes of… (Read More →)

In the modulation of a carrier, one of the values of the signal parameter chosen to represent information.
Note 1: Examples of significant conditions are an electrical current, voltage, or power level; an optical power level; a phase value; or a frequency or wavelength chosen to represent a "0" or a "1"; or a "mark" or a "yyspace. "
Note… (Read More →)

In a representation of a number, a digit that is needed for a given purpose; in particular, a digit that must be kept to preserve a given accuracy or a given precision.

In a signal, any instant at which a significant condition of a signal begins or ends.
Note: Examples of significant instants include the instant at which a signal crosses the baseline or reaches 10% or 90% of its maximum value.

The time interval between two consecutive significant instants.

In digital telephony, a code composed of a reserved binary number that is sent instead of an actual sound sample value from the CODEC when the incoming voice volume is below a certain level (i.e., when there is no sound). Depending on the transmission system used, the silence code is used for two purposes: (a) to allow other (lower priority)… (Read More →)

Any portion of a ringing cycle during which the ringing signal is not being applied. [T1.401-1998]

Synonym skip zone.

Silicon dioxide (SiO2).
Note 1: Silica may occur in crystalline or amorphous form, and occurs naturally in impure forms such as quartz and sand.
Note 2: Silica is the basic material of which the most common communication-grade optical fibers are presently made. [After FAA]

See silica.

A silicon-based PN- or PIN-junction photodiode.
Note 1: Such photodiodes are useful for direct detection of optical wavelengths shorter than approximately 1 m.
Note 2: Because of their greater bandgap, silicon-based photodiodes are quieter than germanium-based photodiodes, but germanium photodiodes must be used for wavelengths longer than approximately 1 m. [FAA]

Session Initiation Protocol for Instant Messaging and Presence Leveraging Extensions

Authentication by means of simple password arrangements. [After X.509]

The assigning of buffer storage for the duration of the execution of a computer program.

See SMTP.

The Transmission Control Protocol/Internet Protocol (TCP/IP) standard protocol that (a) is used to manage and control IP gateways and the networks to which they are attached, (b) uses IP directly, bypassing the masking effects of TCP error correction, (c) has direct access to IP datagrams on a network that may be operating abnormally, thus requiring management, (d) defines a set… (Read More →)

In facsimile transmission, scanning using only one spot at a time.

A Bell-LaPadula security model rule allowing a subject read access to an object only if the security level of the subject dominates the security level of the object [TCSEC].

[The] Bell-La Padula security model rule allowing a subject read access to an object, only if the security level of the subject dominates the security level of the object. [INFOSEC-99]

Signaling in which two conductors are used for a single channel, and a center-tapped coil, or its equivalent, is used to split the signaling current equally between the two conductors.
Note: SX signaling may be one-way, for intra-central-office use, or the simplex legs may be connected to form full duplex signaling circuits that function like composite (CX) signaling circuits with… (Read More →)

1. A circuit that provides transmission in one direction only.
2. Deprecated definition: A circuit using ground return and affording communication in either direction, but in only one direction at a time.
Note: The above two definitions are contradictory; however, both are in common use. The user is cautioned to verify the nature of the service specified by this term.

1. Operation in which transmission occurs in one and only one preassigned direction. Synonym one-way operation.
Note: Duplex operation may be achieved by simplex operation of two or more simplex circuits or channels.
2. Operating method in which transmission is made possible alternately in each direction of a telecommunication channel, for example by means of manual control.
Note: In general,… (Read More →)

A communications protocol that is purely one-way, and where acknowledgments are not part of any application protocol. Error control is either not provided, or is accomplished via forward error correction. [T1.80
0. 08-1995]

To represent certain features of the behavior of a physical or abstract system by the behavior of another system.
Note 1: For example, delay lines may be used to simulate propagation delay and phase shift caused by an actual transmission line.
Note 2: A simulator may imitate only a few of the operations and functions of the unit it simulates.

1. Abbreviation for signal-plus-noise-plus-distortion to noise-plus-distortion ratio.
1. The ratio of (a) total received power, i.e., the received signal-plus-noise-plus-distortion power to (b) the received noise-plus-distortion power.
2. The ratio of (a) the recovered audio power, i.e., the original modulating audio signal plus noise plus distortion powers from a modulated radio frequency carrier to (b) the residual audio power, i.e., noise-plus-distortion… (Read More →)

An undesired self-sustained audio oscillation in a circuit.
Note: Singing is usually caused by positive feedback, excessive gain, or unbalance of a hybrid termination, or by some combination of these.

The difference in power levels between the singing point and the operating gain of a system or component.

The threshold point at which additional gain in the system will cause self-oscillation.

The term "Singing Return Loss" denotes the frequency weighted measure of return loss at the edges of the voice band, where singing (instability) problems are most likely to occur.

Comprising or containing only one security class [CESG].

A device which can only be used to process information of a single security class at a time [CESG]

[A] means of distributing key to multiple, local crypto-equipment or devices from a single fill point. [INFOSEC-99]

A control relationship where the same phase or aspect of a call/service attempt is influenced by one and only one service control function. [T1.667-1999]

Synonym neutral direct-current telegraph system.

Synonym neutral direct-current telegraph system.

Synonym single-ended synchronization.

A feature, e.g., call/service attempt manipulation, that applies to only one of the parties that may be involved on a call/service attempt. [T1.667-1999]

Synchronization between two locations, in which phase error signals used to control the clock at one location are derived by comparing the phase of the incoming signals to the phase of the internal clock at that location. Synonym single-ended control.

In telephony, signaling in which dial pulses or supervisory signals are conveyed by a single voice-frequency tone in each direction.
Note 1: An SF signaling unit converts E & M signaling to a format (characterized by the presence or absence of a single voice-frequency tone), which is suitable for transmission over an ac path, e.g., a carrier system. The SF… (Read More →)

Interference caused by a single-frequency source.
Note 1: An example of single-frequency interference is interference in a transmission channel induced by a 60-Hz source.
Note 2: The interference caused by the single-frequency source may have other frequencies and may also appear in many channels.

Of a fundamental frequency, the ratio of the power of a specified harmonic to the power of the fundamental frequency.
Note: Single-harmonic distortion is measured at the output of a device under specified conditions and is expressed in dB.

1. A functional unit that can only process data of a single security level at a particular time. [2382-pt.8]
2. [An] information system (IS) device not trusted to properly maintain and separate data to different security levels. [INFOSEC-99]
3. A device that is used to process data of a single security level at any one time. Since the device need… (Read More →)

Synonym single-mode optical fiber.

1. An optical fiber in which only the lowest order bound mode can propagate at the wavelength of interest.
Note 1: The lowest order bound mode is ascertained for the wavelength of interest by solving Maxwell's equations for the boundary conditions imposed by the fiber, e.g., core (spot) size and the refractive indices of the core and cladding.
Note 2:… (Read More →)

Synonym single-mode optical fiber.

Synonym neutral direct-current telegraph system.

An antenna that radiates or receives radio waves with a specific polarization.
Note: For a singly polarized antenna, the desired sense of polarization is usually maintained only for certain directions or within the major portion of the radiation pattern.

An amplitude modulated emission with one sideband only. [NTIA] [RR]

The power of one of two equal tones that, when used together to modulate a transmitter, cause it to develop its full rated peak power output.

Sideband transmission in which only one sideband is transmitted.
Note: The carrier may be suppressed.

Single-sideband transmission in which the carrier is suppressed.
Note: In SSB-SC the carrier power level is suppressed to the point where it is insufficient to demodulate the signal.

An undesired discrete frequency appearing in a transmission channel.
Note: The single-tone interference frequency is the frequency that appears in the channel regardless of the nature of the source.

1. An absorber of energy.
2. In communications, a device that receives information, control, or other signals from a source.
3. A location at which a specified multiplex structure is terminated through connected equipment removing the frame alignment signal and disassembling the channel time slots. [T1.107-1988]

Session Initiation Protocol

1. The totality of all of the Internet facilities—http, ftp, etc. —offered by an individual or an organization. [After Bahorsky]
2. A Web location where Web pages are found. Synonym (in this sense) Web site.
Note: A Web site describes only those resources available through the World Wide Web.

Synonym sextet.

1. In parallel transmission, the difference in arrival time of bits transmitted at the same time.
2. For data recorded on multichannel magnetic tape, the difference between reading times of bits recorded in a single transverse line.
Note: Skew is usually interpreted to mean the difference in reading times between bits recorded on the tracks at the extremities, i.e., edges,… (Read More →)

In a multimode optical fiber, a bound ray that travels in a helical path along the fiber and thus (a) is not parallel to the fiber axis, (b) does not lie in a meridional plane, and (c) does not intersect the fiber axis.

The act of producing unauthorized copy of an electronic security device while it is being used for its intended purpose.
Note: Originally, skimming meant making an illegal copy of a credit card or a bank card when the original was being used correctly. Typical methods of skimming involve use of a modified reader that reads and stores all the information… (Read More →)

The tendency of alternating current to flow near the surface of a conductor, thereby restricting the current to a small part of the total cross-sectional area and increasing the resistance to the flow of current.
Note: The skin effect is caused by the self-inductance of the conductor, which causes an increase in the inductive reactance at high frequencies, thus forcing… (Read More →)

SKIP is a trunk group control that allows traffic to be directed to the next route before hunting for a circuit to a destination. Equipment vendors commonly provide the capability to implement this control on a percentage basis.

At a given azimuth, the minimum distance between the transmitting station and the closest point of return to the Earth of a transmitted wave reflected from the ionosphere.

An annular region within the transmission range of an antenna, within which signals from the transmitter are not received.
Note: The skip zone is bounded by the locus of the farthest points at which the ground wave can be received and the nearest points at which reflected sky waves can be received. Synonyms silent zone, zone of silence.

See Clipper

A radio wave that travels upward from the antenna.
Note: A sky wave may be reflected to Earth by the ionosphere.

Service Level Agreement

An electromagnetic waveguide (a) that consists solely of dielectric materials, (b) in which the dielectric propagation medium has a rectangular cross section, (c) that has a width, thickness, and refractive indices that determine the operating wavelength and the modes the guide will support beyond the equilibrium length, (d) that may be cladded, protected, distributed, and electronically controllable, and (e) that… (Read More →)

The action that occurs when a customer's long-distance telephone service (carrier selection) is switched from one long distance company to another without the customer's permission, and often, knowledge. [After FCC]

The line-of-sight distance between two points, not at the same level relative to a specific datum. [JP 1-02]
Note: An example of slant range is the distance to an airborne radar target, e.g., an airplane flying at high altitude with respect to that of the radar antenna. The slant range is the hypotenuse of the triangle represented by the altitude… (Read More →)

A clock that is coordinated with a master clock.
Note 1: Slave clock coordination is typically achieved by phase-locking the slave clock output signal to a signal coherent with, or whose clocking source is traceable to, the master clock.
Note 2: If it is necessary to adjust for the transit time of the signal from the master clock to the… (Read More →)

1. In a data network, a station that is selected and controlled by a master station.
Note: Usually a slave station can only call, or be called by, a master station.
2. In navigation systems using precise time dissemination, a station having a clock is synchronized by a remote master station. Synonym subordinate station.

1. Rotating a directional antenna or transducer rapidly about one or more axes.
2. Changing the frequency or pulse repetition rate of a signal source.
3. Changing the tuning of a receiver, usually by sweeping through many or all frequencies. [From Weik '89]
4. Redirecting the beam of a fixed antenna array by changing the relative phases of the signals… (Read More →)

Subscriber Location Function

A variable-duration window that allows a sender to transmit a specified number of data units before an acknowledgement is received or before a specified event occurs.
Note: An example of a sliding window in packet transmission is one in which, after the sender fails to receive an acknowledgement for the first transmitted packet, the sender "slides" the window, i.e., resets… (Read More →)

Acronym for serial line Internet protocol. A protocol that allows a computer to use the Internet protocol (IP) with a standard telephone line and a high-speed modem.

1. The repetition or deletion of a block of bits in a synchronous or perspicacious bitstream due to a discrepancy in the read and write rates at a buffer. [T1.101-1987]
2. In a sequence of transmitted symbols, e.g., digital bits, a signal phase shift, i.e., a signal positional displacement, that causes the loss of one or more symbols or the… (Read More →)

Operation of a communications system with sufficient phase-locking to avoid overflowing or emptying buffers.

Synonym line source.

In a transmission line, the rate of change of attenuation with respect to frequency over the frequency spectrum.
Note 1: The slope is usually expressed in dB per hertz or dB per octave.
Note 2: In metallic lines, the slope is usually greater at high frequencies than at low frequencies.

A device or circuit used to achieve a specified slope in a metallic transmission line.

Data compaction accomplished by stating (a) a specific keypoint of departure, (b) a direction or slope of departure, (c) the maximum deviation from a prescribed specific value, and (d) a new keypoint and a new slope.
Note: An example of slope-keypoint compaction is the storage or transmission of a slope and one point on a straight line instead of storing… (Read More →)

In a distributed-queue dual-bus (DQDB) network, a protocol data unit (PDU) that (a) consists of 53 octets used to transfer segments of user information, (b) has the capacity to contain a segment of 52 octets and a 1-octet access control field, and (c) may be either a pre-arbitrated (PA) slot or a queued arbitrated (QA) slot.

A radiating element formed by a slot in a conducting surface or in the wall of a waveguide.

In networks using carrier sense multiple access with collision detection (CSMA/CD), the length of time that a transmitting station waits before attempting to retransmit following a collision.
Note: Slot time varies from station to station.

A ring network that allows unidirectional data transmission between data stations by transferring data in predefined slots in the transmission stream over one transmission medium such that the data return to the originating station.

Service Location Protocol

Service Management & Operations

A computer form factor designed to minimize the volume and footprint of a desktop computer.

Abbreviation for smart robot. See bot.

A digitally encoded card, similar to a credit card, usually containing a variety of information about the individual(s) authorized to use it.
Note: The information can be accessed by a card reader into which the card is inserted. The information may include access codes (for opening doors), account numbers (merchant account numbers as well as banking account numbers), and electronic… (Read More →)

Synonym [loosely] continuity check transponder.

See bot.

Server Message Block Protocol

Abbreviation for station message-detail recording.

In video displays, a localized distortion over a sub-region of the image, characterized by reduced sharpness of edges and spatial detail. For example, the portrayal of a fast moving object may exhibit smearing. [T1.80
1. 02-1996]

Storage Management Specification

Acronym for synchronized multimedia integration language. A protocol for downloading digitized streams or audio/video data files in the absence of a browser.
Note: Pronounced "smile. "

Standard Markup Language

Idealized surfaces, such as water surfaces or very level terrain, having radio horizons that are not formed by prominent ridges or mountains but are determined solely as a function of antenna height above ground and the effective Earth radius.

Society of Motion Picture and Television Engineers

Short Message Service Center

Abbreviation for simple mail transfer protocol. A protocol used to transfer e-mail between or among servers.
Note: End-users then employ Post Office Protocol to transfer messages to individual terminals.

Abbreviation for systems network architecture. A proprietary communications architecture.

In a communications circuit, an anomalous current that presents no immediate danger, but may cause improper operation or damage.

Application of a protective device that is intended to limit currents that are too small to operate fuse links, stub cables, or the fuse of a fused primary protector. [T1.318-2000]

A law of geometric optics that defines the amount of bending that takes place when a light ray strikes a refractive boundary, e.g., an air-glass interface, at a non-normal angle.
Note 1: Snell's law states that where n₁ is the index of refraction of the medium in which the incident ray travels, ₁ is the angle, with respect to the… (Read More →)

[A] software tool for auditing and identifying network traffic packets. [INFOSEC-99]
Note: An example of a sniffer is a packet sniffer.

Abbreviation for Simple Network Management Protocol.

In video display systems, noise that (a) is uniformly distributed on the display surface, such as that of a television or radar screen, (b) has the appearance of a uniform distribution of fixed or moving spots, mottling, or speckling, and (c) is usually caused by random noise on an intensity-modulated signal in a display device, such as a cathode-ray tube.

Abbreviation for signal-to-noise ratio.

Simple Network Time Protocol

Service Order Administration

Simple Object Access Protocol

Service Order Entry

A nonpermanent display image, for example, a cathode ray tube display.

Numbers that permit restricted dialing, such as calling emergency services and sometimes receive incoming calls (FCC 00-104, ¶ 33). See “Administrative Numbers” definition.

See limiting.

On magnetic disks, magnetic drums, and optical disks, the identification of sector boundaries by using recorded information.

See Call Agent

1. A set of computer programs, procedures, and associated documentation concerned with the operation of a data processing system; e.g., compilers, library routines, manuals, and circuit diagrams. [JP 1-02]
2. Information (generally copyrightable) that may provide instructions for computers; data for documentation; and voice, video, and music for entertainment or education.
3. The programs, procedures, rules, and any associated documentation… (Read More →)

A radio consisting of a receiver and/or a transmitter, where each has the following properties, respectively: (a) the received signal is digitized and then processed using software-programmable digital signal processing techniques (digitization may occur at the rf, IF, or baseband); (b) the modulated signal to be transmitted is generated as a digital signal using software-programmable digital signal processing techniques; the… (Read More →)

The discipline devoted to the design, development, and use of computer software.
Note: Software engineering must address various aspects of data processing, including compatibility with the computer system which is to execute the software, and tradeoffs among maintainability, flexibility, efficiency, processing time, and costs. [From Weik '89]

A package that consists of (a) one or more computer programs and possibly related material such as utility programs or tutorial programs, recorded on a medium suitable for delivery to the user, and from which the user can transfer the program(s) to a data-processing device, and (b) instructional materials such as handbooks and manuals, update information, and possibly support services… (Read More →)

The unauthorized use, copying, or distribution of software products. [2382-pt.8]

Software, such as a computer program, routine, subroutine, program block, or program module, that can be used to develop, test, analyze, or maintain a computer program or its documentation.
Note: Examples of software tools are automated software verification routines, compilers, program maintenance routines, bootstraps, program analyzers, and software monitors. [From Weik '89]

Abbreviation for start-of-heading character.

Small Office/Home Office

Service Oriented Infrastructure

In facsimile, scanning in which all or a part of the scanning process is performed by electronic commutation of an array of solid-state photosensitive elements.

An optical pulse having a shape, spectral content, and power level designed to take advantage of nonlinear effects in an optical fiber waveguide, for the purpose of essentially negating dispersion over long distances.

Service Oriented Networks

Acronym for sound navigation and ranging. A device that is used primarily for the detection and location of underwater objects by reflecting acoustic waves from them, or by the interception of acoustic waves from an underwater, surface, or above-surface acoustic source.
Note: Sonar operates with acoustic waves in the same way that radar and radio direction-finding equipment operate with electromagnetic… (Read More →)

Acronym for synchronous optical network. An interface standard for synchronous optical-fiber transmission, applicable to the Physical Layer of the OSI Reference Model.
Note: SONET uses a basic bit rate of
5
1. 840 Mb/s, called OC-1 (optical carrier 1). The SONET hierarchy consists of preset integral multiples of OC-1, i.e., OC-3, OC-12, OC-48, etc. [T
1. X1]

In sonar systems, a device (a) that is used to detect acoustic waves, such as those produced by ships and submarines, (b) that, when activated, relays information by radio, (c) that may be active or passive, and (d) that may be directional or nondirectional. [From Weik '89]

See sonar.

See acoustic wave.

A telephone in which the operating power is derived from the speech input only.

A station equipped with an ionosphere sounder for realtime monitoring of upper atmosphere phenomena or to obtain data for the prediction of propagation conditions. [NTIA]

In automated HF radio systems, the broadcasting of a very brief signal, containing the station address, station identifier, or call sign, to permit receiving stations to measure link quality.

In communications, that part of a system from which messages are considered to originate.

In optical systems, the ratio of emitted optical power of a source to the input electrical power.

In computing, data processing, and communications systems, a language from which statements are translated.
Note: Translators, assemblers, and compilers prepare target language programs, usually machine-language programs, from source language programs, usually high-level language programs written by programmers.

1. A computer program written in a source language.
Note: An example of a source program is a program that serves as the input to an assembler, compiler, or translator.
2. A computer program that must be assembled, compiled, or translated before it can be executed by a computer. [From Weik '89]

A congestion-control technique in which a computer experiencing data traffic congestion sends a message back to the source of the messages or packets causing the congestion, requesting that the source stop transmitting.

The user providing the information to be transferred to a destination user during a particular information transfer transaction. Synonym information source.

SSM uses both the source and the group address to identify the session traffic as noted as (S,G). SSM-enabled protocols are able to differentiate between (SI, G) and (S2, G) as unique multicast groups allowing a group address to be reused by different multicast sources.

Service Provider

In telegraphy, one of the two significant conditions of encoding.
Note 1: The complementary significant condition is called a "mark. "
Note 2: In modern digital communications, the two corresponding significant conditions of encoding are called "zero" and "one. " Synonyms spacing pulse, spacing signal.

A method of transmission or reception, or both, in which the effects of fading are minimized by the simultaneous use of two or more physically separated antennas, ideally separated by one or more wavelengths.

A radiocommunication service concerned exclusively with the operation of spacecraft, in particular space tracking, space telemetry and space telecommand. These functions will normally be provided within the service in which the space station is operating. [NTIA] [RR] [47CFR]

Any radiocommunication involving the use of one or more space stations or the use of one or more reflecting satellites or other objects in space. [NTIA] [RR] [47CFR]

A radiocommunication service in which spacecraft or other objects in space are used for scientific or technological research purposes. [NTIA] [RR]

A station located on an object which is beyond, is intended to go beyond, or has been beyond, the major portion of the Earth's atmosphere. [NTIA] [RR] [47CFR]

In satellite communications, that portion of the satellite link that is in orbit.

Any group of cooperating Earth stations and/or space stations employing space radiocommunication for specific purposes. [NTIA] [RR] [47CFR]

1. The use of radiocommunication for the transmission of signals to a space station to initiate, modify or terminate functions of equipment on an associated space object, including the space station. [NTIA] [RR]
2. The use of radiocommunication for the transmission of signals to a space station to initiate, modify or terminate function of the equipment on a space object,… (Read More →)

The use of telemetry for the transmission from a space station of results of measurements made in a spacecraft, including those relating to the functioning of spacecraft. [NTIA] [RR]

Determination of the orbit, velocity or instantaneous position of an object in space by means of radiodetermination, excluding primary radar, for the purpose of following the movement of the object. [NTIA] [RR] [47CFR]

A misnomer.
Note: Space-division multiplexing has been improperly applied to the use of multiple physical transmission channels, e.g., twisted pairs or optical fibers, under one sheath.

In telephony, switching in which single transmission-path routing determination is accomplished in a switch by using a physically separated set of matrix contacts or cross-points.

A man-made vehicle which is intended to go beyond the major portion of the Earth's atmosphere. [NTIA] [RR] [47CFR]

The uniform lengthening of all spacing signal pulses at the expense of the pulse width of all marking signal pulses.

See end distortion.

Synonym yyspace.

Synonym yyspace.

1. Slang
1. Unwanted or unsolicited e-mail messages or mailing-list or newsgroup postings.
2. To send an advertisement or solicitation to large numbers of unsolicited recipients, usually via mailing lists or newsgroups. [Bahorsky]

Synonyms [in e-mail] flooding, mail bombing.

An individual part, subassembly, or assembly supplied for the maintenance or repair of systems or equipment.

Simple Protocol and RDF Query Language

An application requiring high spatial resolution, possibly at the expense of reduced temporal positioning accuracy, i.e., increased jerkiness.
Note: Examples of spatial applications include the requirement to display small characters and to resolve fine detail in still video, or in motion video that contains very limited motion.

See coherent.

In a video display, that form of edge busyness that is characterized by spatially varying distortion that occurs in close proximity to the edges of objects.

See coherent.

Session Protocol Data Unit

In the Defense Switched Network, an access line specially conditioned, usually by providing amplitude and delay equalization, to give it characteristics suitable for handling special services, such as reducing data signaling rates (DSR) to a rate between 600 b/s and 2400 b/s.

In the Defense Switched Network, a network-provided service in which specially conditioned interswitch trunks and access lines are used to provide secure voice, data, and facsimile transmission.

A tone that comprises three precise sequential frequencies used to identify recorded announcements. [After T1.207-1998]

See community of interest, interest group, forum, SIG.

A computer that is designed to operate on a restricted class of problems.

A radiocommunication service, not otherwise defined in this Section [of the Radio Regulations], carried on exclusively for specific needs of general utility, and not open to public correspondence. [RR with editor's note in brackets]

All services other than message telephones, e.g., teletypewriter exchange service (TWX), private line services. [47 CFR Pt.36-A]

A common carrier offering a limited type of service or serving a limited market.

For a photodetector, a figure of merit used to characterize performance, equal to the reciprocal of noise equivalent power (NEP), normalized to unit area and unit bandwidth.
Note: Specific detectivity, D*, is given by ,f44 where A is the area of the photosensitive region of the detector and f is the effective noise bandwidth. Synonym D-Star.

1. An essential technical requirement for items, materials, or services, including the procedures to be used to determine whether the requirement has been met.
Note: Specifications may also include requirements for preservation, packaging, packing, and marking.
2. An official document intended primarily for supporting procurement, which document clearly and accurately describes the essential technical requirements for items, materials, or services,… (Read More →)

An industry agreed-upon location where a set of specifications would apply, for example, the node in the originating network where specification occurs. [After T1.118-1992]

Synonym modal noise.

In optical systems, a field-intensity pattern produced by the mutual interference of partially coherent beams that are subject to minute temporal and spatial fluctuations.
Note: In a multimode fiber, a speckle pattern results from a superposition of mode field patterns. If the relative modal group velocities change with time, the speckle pattern will also change with time. If differential mode… (Read More →)

See spectral width.

For a specified bandwidth of radiation consisting of a continuous frequency spectrum, the total power in the specified bandwidth divided by the specified bandwidth.
Note: Spectral density is usually expressed in watts per hertz.

Irradiance per unit wavelength interval at a given wavelength, usually expressed in watts per unit area per unit wavelength interval.

A narrow range of emitted or absorbed wavelengths.

Of an optical fiber, a plot of attenuation as a function of wavelength.
Note: Spectral loss curves must be normalized with respect to distance before meaningful comparison among fibers can be made.

The degree to which a signal is monochromatic.

Radiance per unit wavelength interval at a given wavelength, expressed in watts per steradian per unit area per wavelength interval.

The ratio of an optical detector's electrical output to its optical input, as a function of optical wavelength.

The wavelength interval over which the magnitude of all spectral components is equal to or greater than a specified fraction of the magnitude of the component having the maximum value.
Note 1: In optical communications applications, the usual method of specifying spectral width is the full width at half maximum. This method may be difficult to apply when the spectrum… (Read More →)

See window.

See electromagnetic spectrum, optical spectrum.

See electromagnetic spectrum.

The pattern of radio signal frequencies, amplitudes, and phases, which pattern characterizes the output of a particular device and tends to distinguish it from other devices.

Reflection from a smooth surface, such as a mirror, which maintains the integrity of the incident wavefront.

Synonym bit robbing.

The power in dBm of a speech signal measured using a technique equivalent to Method B of ITU-T Recommendation P.5
6. [T1.255-1997]

See volume unit.

Techniques using fixed sequence permutations or voice/speech inversion to render speech unintelligible to the casual listener. [INFOSEC-99]

A device that is capable of accepting digital or analog data and developing intelligible speech sounds that correspond to the input data, without resorting to recorded sounds or without simply being a speech scrambler operating in reverse. [From Weik '89]

Pertaining to a circuit that was designed and used for speech transmission, but to which other uses, such as digital data transmission, facsimile transmission, telegraph, or signaling superimposed on the speech signals, have been added by means of multiplexing. [From Weik '89]

Operation in which speech and telegraphy (duplex or simplex) are transmitted simultaneously over the same circuit, and mutual interference is eliminated by the use of filters.

Pertaining to equipment that permits the use of part of a voice-frequency band for signaling.

The ratio of the speech power to the power of speech-correlated noise in a digital transmission system. [T1.501-1988]

A service feature that enables a switch or station to store certain telephone numbers and dial them automatically when a short (1-, 2-, or 3-digit) code is entered.

1. Synonym abbreviated dialing.
2. Dialing at a speed greater than the normal ten pulses per second.

The speed of an electromagnetic wave in free space, precisely 299,792,458 m/s.
Note 1: The preceding figure is precise because by international agreement the meter is now defined in terms of the speed of light.
Note 2: The speed of an electromagnetic wave, e.g., light, is equal to the product of the wavelength and the frequency.
Note 3: In any… (Read More →)

1. The time between release of a message by the originator to receipt of the message by the addressee, as perceived by the end user. Synonym originator-to-recipient speed of service.
2. The time between entry of a message into a communications system and receipt of the message at the terminating communications facility, i.e., the communications facility serving the addressee, as… (Read More →)

Synonym camp-on busy signal.

Service Provider ID

See bot, droid.

An extremely short pulse of relatively high amplitude.

See last-in first-out.

In automatic switching, the transfer of full control on a call to the succeeding office by sending forward the complete telephone address of the called party.

A service feature, in the operation of an intermediate office, that, acting on incoming trunk service treatment indications, assumes routing control of the call from the originating office.
Note: This increases the chances of completion by offering the call to more trunk groups than are available in the originating office.

In an antenna, the part of the radiated energy from the feed that does not impinge on the reflectors.

A track with a spiral shape written on a diskette, as part of a method of copy protection. [2382-pt.8]

A molded, insulated plastic product in the form of a helix, used to contain or dress electrical wiring, e.g., to create a wiring harness from a number of insulated wires.

A quadded cable with four conductors. Synonym star quadded cable.

1. To join, permanently, physical media that conduct or transmit power or a communication signal.
2. A device that so joins conducting or transmitting media.
3. The completed yyjoint.

A usually weatherproof encasement, commonly made of tough plastic, that envelops the exposed area between spliced cables, i.e., where the jackets have been removed to expose the individual transmission media, optical or metallic, to be joined.
Note 1: The closure usually contains some device or means to maintain continuity of the tensile strength members of the cables involved, and also… (Read More →)

In fiber optic systems, any loss of optical power at a splice.
Note: A practical splice, of physically realizable fibers, has losses attributable to a number of mechanisms, some of which are intrinsic to the fibers, and some of which are intrinsic to the method or device being used to join them. [After FAA]

In optical communication, a device that facilitates the splicing or breaking out of fiber optic cables.
Note: The organizer provides means to separate and secure individual buffer tubes, fibers, and/or pigtails. It also provides means to secure mechanical splices or protective sleeves used in connection with fusion splices, and has means to contain the slack fiber that remains after the… (Read More →)

1. With respect to a signal, to divert a portion of it, or divide it, into usually predetermined or specified proportions.
2. In INFOSEC, a secret random number that is a component of the final working key. [After X9.69]
3. An action that creates a private communication between the served user and a conferee. The private communication is a normal… (Read More →)

The connection of a terminal facility to more than one switching center by separate access lines, each of which has a separate directory number.

1. In secure communications, a condition under which two or more entities separately have key components that, individually, convey no knowledge of the resultant cryptographic key. [After X9.24]
2. Separation of data or information into two or more parts, each part constantly kept under control of separate authorized individuals or teams so that no one individual or team will know… (Read More →)

On a display device, display space that has been divided into two or more areas, so that each area can display different portions of the same file or portions of different files.
Note 1: The split screen excludes the data lying between the portions of the file or files being displayed and includes the desired data in the two or… (Read More →)

See directional coupler, T-coupler, tee coupler.

The person or organization that requests an evaluation [ITSEC].

A certificate that indicates the restrictions on those documents and transactions that an entity may authorize. [After X9.45]

Radiation emitted when the internal energy of a quantum mechanical system drops from an excited level to a lower level without regard to the simultaneous presence of similar radiation.
Note: Examples of spontaneous emission include radiation from an LED, and radiation from an injection laser below the lasing threshold.

1. (COMSEC) [The] interception, alteration, and retransmission of a cipher signal or data in such a way as to mislead the recipient. [NIS]
2. (AIS) [An] attempt to gain access to an AIS by posing as an authorized user. [NIS]
3. Unauthorized use of legitimate Identification and Authentication (I&A) data, however it was obtained, to mimic a subject different from… (Read More →)

The use of auxiliary storage as buffer storage to reduce processing delays when transferring data between peripheral equipment and the processors of a computer.
Note: The term is derived from the expression "simultaneous peripheral operation on line. "

Irregular scattered patches of relatively dense ionization that develop seasonally within the E region and that reflect and scatter frequencies up to 150 MHz.
Note 1: The sporadic E is a regular daytime occurrence over the equatorial regions and is common in the temperate latitudes in late spring, early summer and, to a lesser degree, in early winter.
Note 2:… (Read More →)

Synonym sporadic E.

In satellite communications systems, a narrow beam from a satellite station antenna that illuminates, with high irradiance, a limited area of the Earth by using beam (directive) antennas rather than Earth-coverage antennas.

The jamming of a specific channel or frequency. [JP 1-02]

In facsimile systems, optical scanning in which a scanning spot is moved across the object and the scanning spot size is determined by the illuminated area of the spot.

1. The size of the electron spot on the face of a cathode ray tube.
Note: The spot size is larger than the diameter of the electron beam because of the spillover of electrons into adjacent areas of the screen near the spot. The spot size is a function of the ability of the tube to focus the electron beam,… (Read More →)

In facsimile systems, the speed of the scanning or recording spot along the available line.
Note: The spot speed is usually measured on the object or on the recorded copy.

Supplemental Port Request

Supplemental Port Request 1 – Cancel

Supplemental Port Request 2 – Change Date

Supplemental Port Request 3 – Update Data

1. Telecommunications techniques in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information.
Note: Frequency hopping, direct sequence spreading, time scrambling, and combinations of these techniques are forms of spread spectrum. [INFOSEC-99]
2. A signal structuring technique that employs direct sequence, frequency hopping or a hybrid of these, which can be… (Read More →)

Single Program Transport Stream

A secondary route having a junction to the primary route in a network.

Emission on a frequency or frequencies which are outside the necessary bandwidth and the level of which may be reduced without affecting the corresponding transmission of information. Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products, but exclude out-of-band emissions. [NTIA] [RR]

Circuit noise or interference that is like a signal. [T1.401-1988]

Any unintentional emission.

In radio reception, a response in the receiver intermediate frequency (IF) stage produced by an undesired emission in which the fundamental frequency (or harmonics above the fundamental frequency) of the undesired emission mixes with the fundamental or harmonic of the receiver local oscillator.

Any tone that (a) is other than a fundamental tone or its harmonics, and (b) is generated within the back-to-back connected transmit and receive terminal or channel units, when the fundamental, i.e., a test sine wave, is applied to the transmit terminal or channel unit input. [After T1.305-1990]

Abbreviation for structured query language. The international standard language for defining and accessing relational databases. [Bahorsky]

Service Quality Management

A pixel of equal width and height; i.e., having an aspect ratio of 1:1
Note: Pixels created by computer graphics usually have an aspect ratio of 1:
1. Television technology was not always concerned with pixel aspect ratio. However, modern dependence upon digital electronic post-production (e.g., image distortion, rotation, or size changes) has underscored the advantages of square pixels, which… (Read More →)

A wave that has two significant conditions, i.e., two levels of amplitude, that change from one condition to the other in a relatively short time compared to the wavelength.
Note: When the instantaneous amplitude is plotted versus time or distance, the waveform has a rectangular shape. [From Weik '89]

See cybersquatting.

A circuit function that acts to suppress the audio output of a receiver. [NTIA]
Note: The squelch function is activated in the absence of a sufficiently strong desired input signal, in order to exclude undesired lower-power input signals that may be present at or near the frequency of the desired signal.

Abbreviation for steradian.

1. Selective Router,
2. Sustainable Rate.

SeRVice Record (see DNS)

Abbreviation for Signaling System No.7.

Abbreviation for single sideband. See single-sideband emission.

Abbreviation for single-sideband suppressed carrier. See single-sideband suppressed carrier transmission.

Simple Service Discovery Protocol

Secure Sockets Layer

Source-Specific Multicast

Single Sign On

The invariability of a specified property of a substance, device, or apparatus with time, or under the influence of typically extrinsic factors.

In facsimile systems, periodic error in the position of the recorded spot along the recorded line.

1. Guideline documentation that reflects agreements on products, practices, or operations by nationally or internationally recognized industrial, professional, trade associations or governmental bodies.
Note: This concept applies to formal, approved standards, as contrasted to de facto standards and proprietary standards, which are exceptions to this concept.
2. An exact value, a physical entity, or an abstract concept, established and defined… (Read More →)

A radiocommunication service for scientific, technical and other purposes, providing the transmission of specified frequencies, time signals, or both, of stated high precision, intended for general reception. [NTIA] [RR]

A station in the standard frequency and time signal service. [NTIA] [RR]

A radiocommunication service using space stations on Earth satellites for the same purpose as those of the standard frequency and time signal service. This service may also include feeder links necessary for its operation. [NTIA] [RR]

See SGML.

The set of conditions (e.g., voltage, temperature, humidity, and the like) over which the specified parameters maintain their stated performance rating. [T1.106-1988]

A reference optical source to which emitting and detecting devices are compared for calibration purposes.
Note: In the United States, recognized standard optical sources must be traceable to the National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards (NBS).

The power per individual telegraph channel required to yield the standard composite data level.
Note: For example, for a composite data level of -13 dBm at 0-dBm transmission level point (0TLP), the STL would be approximately -25 dBm for a 16-channel VFCT terminal computed from STL = - (13+10log10 n), where n is the number of telegraph channels and the… (Read More →)

A single-frequency signal with standardized level used for testing the peak power transmission capability and for measuring the total harmonic distortion of circuits or parts of a circuit.
Note: Standardized test signal levels and frequencies are listed in MIL-STD-188-100 and in the Code of Federal Regulations, Title 47, part 68.

A single-frequency signal with a standardized level generally used for level alignment of single links and of links in tandem.
Note: For standardized test signal levels and frequencies, see MIL-STD-188-100 for DOD use, and the Code of Federal Regulations, Title 47, part 68 for other Government agencies.

In the United States, standard time and frequency signals, broadcast on very precise carrier frequencies by the U. S. Naval Observatory and the National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards (NBS).
Note: The Radio Regulations (RR) define an identical international service as standard frequency and time signal service.

1. A profile that specifies one or more interoperable open systems interconnection stacks that are intended to cover one or more specific functional areas.
Note: Examples of standardized profiles are the ISO standardized profiles and the NATO standardized profiles.
2. A balloted, formal, harmonized document that specifies a profile [POSIX.0].

Documents, established by consensus and approved by a recognized body that provides, for common and repeated use, rules, guidelines, or characteristics for activities or their results, aimed at the achievement of the optimum degree of order in a given context [POSIX.0].

An organization that develops standards and is accredited by its National Body, as appropriate [POSIX.0]

1. In computer and communications systems operations, pertaining to a power-saving condition or status of operation of equipment that is ready for use but not in use.
Note: An example of a standby condition is a radio station operating condition in which the operator can receive but is not transmitting.
2. Pertaining to a dormant operating condition or state of… (Read More →)

In a transmission line, a wave in which the distribution of current, voltage, or field strength is formed by the superposition of two waves propagating in opposite directions, and which wave is characterized by a series of nodes (maxima) and anti-nodes (minima) at fixed points along the transmission line.
Note: A standing wave may be formed when a wave is… (Read More →)

The ratio of the amplitude of a standing wave at an anti-node (minimum) to the amplitude at an adjacent node (maximum).
Note 1: The standing wave ratio (SWR) in a uniform transmission line is given by where is the reflection coefficient.
Note 2: Reflections occur as a result of discontinuities, such as an imperfection in an otherwise uniform transmission line,… (Read More →)

1. [The] Bell-La Padula security model rule allowing a subject write access to an object only if the security level of the object dominates the security level of the subject. [INFOSEC-99]
2. A Bell-LaPadula security model rule allowing a subject write access to an object only if the security level of the subject is dominated by the security level of… (Read More →)

A passive optical coupler having a number of input and output ports, used in network applications.
Note: An optical signal introduced into any input port is distributed to all output ports. Because of the nature of the construction of a passive star coupler, the number of ports is usually a power of 2; i.e., two input ports and two output… (Read More →)

See network topology.

Synonym spiral-four cable.

See network topology.

Synonym go-ahead notice.

Synonym go-ahead notice.

See A-condition, start signal.

1. A signal that prepares a device to receive data or to perform a function.
2. In start-stop transmission, a signal at the beginning of a character that prepares the receiving device for the reception of the code elements.
Note: A start signal is limited to one signal element usually having the duration of a unit interval.

An on-hook signal indicating customer installation (CI) readiness to receive network outpulsing that is used in conjunction with controlled outpulsing. The on-hook signal that ends the wink-start signal or delay-dial signal is the start-dial signal. [T1.405-1989]

A transmission control character used as the first character of a message heading.

A transmission control character that precedes a text and may be used to terminate the message heading.

In facsimile systems, a signal used for starting the process of converting the electrical signal to an image on the record medium.

A character that includes one start signal at the beginning and one or two stop signals at the end.

In start-stop modulation, the ratio of (a) the maximum absolute difference between the actual and the theoretical intervals that separate any significant instant of modulation or demodulation from the significant instant of the start signal element immediately preceding it to (b) the unit interval.

In start-stop modulation, the maximum amount of overall start-stop distortion that is compatible with correct translation by the start-stop equipment of all the character signals that appear singly, that appear at the maximum allowable speed, or that appear at the standard modulation rate.

A method of modulation in which the time of occurrence of the bits within each character, or block of characters, relates to a fixed time frame, but the start of each character, or block of characters, is not related to this fixed time frame.

Synonym asynchronous communications system.

1. Asynchronous transmission in which a start pulse and a stop pulse are used for each symbol.
2. Signaling in which each group of code elements corresponding to an alphanumeric character is (a) preceded by a start signal that serves to prepare the receiving mechanism for the reception and registration of a character and (b) followed by a stop signal… (Read More →)

Synonym teletypewriter signal distortion.

Key-encryption-key held in common by a group of potential communicating entities and used to establish ad hoc tactical networks. [INFOSEC-99]

A specified bit pattern that indicates the start of a transmission frame.

1. In programming languages, a language construct that represents a set of declarations or a step in a sequence of actions.
2. In computer programming, a symbol string or other arrangement of symbols.
3. In computer programming, a meaningful expression or generalized instruction, represented in a source language.

Data that are relatively long-lived in comparison to ephemeral data, and which have a longer period of validity.
Note: Static data may include static domain parameters and static public or private keys. Both static and ephemeral data are valuable ingredients for building robust key agreement protocols. [After X9.42]

See serial-to-parallel conversion.

One or more transmitters or receivers or a combination of transmitters and receivers, including the accessory equipment, necessary at one location for carrying on a radiocommunication service, or the radio astronomy service. Each station shall be classified by the service in which it operates permanently or temporarily. [NTIA] [RR]

Within a facility, a separate battery power source that satisfies all significant requirements for dc input power associated with the facility.
Note: Station batteries are usually centrally located. The batteries may power radio and telephone equipment as well as provide emergency lighting and controls for the equipment.

In a station, the principal clock, or alternate clock, that provides the timing reference at the station.

See customer premises equipment.

The total power requirements of the integrated station facilities.

A record of all calls originated or received by a switching system.
Note: SMDRs are usually generated by a computer.

The term applied to the basis of toll rate making which contemplates that the message toll service charge (telephone or TWX) covers the use made of all facilities between the originating station and the terminating station, including the stations, and the services rendered in connection therewith. [47 CFR Pt.36-A]

See geostationary orbit.

Synonym standing wave.

Multiplexing in which channels are established on a statistical basis; i.e., connections are made according to probability of need.

Time-division multiplexing in which connections to communication circuits are made on a statistical basis.

A characteristic of a quantity such that, for an n-bit quantity, the probability of two values' repeating is less likely than or equal to the probability of two n-bit quantities' repeating at random. [After X9.62]

The bits of a link status signal unit that indicate one of the major signaling link states. [T1.226-1992]

A unit of distance equal to
1. 609 km (
0. 869 nmi, 5280 ft. ).

Set Top Box

System Time Clock

Subscriber Trunk Dialing

Abbreviation for statistical time-division multiplexing.

1. In a communications circuit, a condition in which some specified characteristic of a condition, such as a value, rate, periodicity, or amplitude, exhibits only negligible change over an arbitrarily long period.
2. In an electrical circuit, the condition that exists after all initial transients or fluctuating conditions have damped out, and all currents, voltages, or fields remain essentially constant,… (Read More →)

The value to which a throughput measurement converges, as the duration of the observation period increases with statistically constant load on the virtual connection. [After T1.504-1989]

A variety of encryption that completely hides text or graphics, usually unencrypted, within other text or graphics that are electronically transmitted.

An automatic dial telephone system in which calls are switched by a succession of switches that move a step at a time, from stage to stage, each step being made in response to the dialing of a number.

An optical fiber with a core having a uniform refractive index.

For an optical fiber, a refractive index profile characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the core-cladding interface.
Note 1: The step-index profile corresponds to a power-law index profile with the profile parameter approaching infinity.
Note 2: The step-index profile is used in most single-mode fibers and some multimode fibers.

The metric unit of solid angle. See International System of Units.

An undesired signal occurring in the main channel from modulation of the stereophonic channel or that occurring in the stereophonic channel from modulation of the main channel. [47CFR]

A subcarrier within the FM broadcast baseband used for transmitting signals for stereophonic sound reception of the main broadcast program service. [47CFR]

Abbreviation for standard time and frequency signal. See standard time and frequency signal service.

Nonmoving visual information, i.e., fixed images, such as graphs, drawings, and pictures.

Video imagery that is not intended to convey the appearance of movement.

In a quantum mechanical system, the radiation emitted when the internal energy of the system drops from an excited level (induced by the presence of radiant energy at the same frequency) to a lower level.
Note: An example of stimulated emission is the radiation from an injection laser diode operated above the lasing threshold.

Abbreviation for standard telegraph level, studio-to-transmitter link, Satellite Time and Location.

See stop signal.

1. In start-stop transmission, a signal at the end of a character that prepares the receiving device for the reception of a subsequent character. A stop signal is usually limited to one signal element having any duration equal to or greater than a specified minimum value.
2. A signal to a receiving mechanism to wait for the next signal.

In facsimile systems, a signal used for stopping the process of converting the electrical signal to an image on the record medium.

A band of frequencies, between specified limits, that a circuit, such as a filter or telephone circuit, does not transmit.
Note 1: Frequencies above the lower limit and below the upper limit are not transmitted, i.e., are not allowed to pass.
Note 2: The limiting frequencies are those at which the transmitted power level increases to a specified level, usually… (Read More →)

1. The retention of data in any form, usually for the purpose of orderly retrieval and documentation. [JP 1-02]
2. A device consisting of electronic, electrostatic, electrical, hardware, or other elements into which data may be entered, and from which data may be obtained, as desired. [JP 1-02]

1. An addressable storage unit.
2. The smallest subdivision of storage into which a unit of data can be entered, stored, and retrieved. Synonym storage element.

Synonym storage cell.

1. An object supporting both read and write accesses to an information system (IS). [INFOSEC-99]
2. an object that supports both read and write accesses[ITSEC].
3. An object that supports both read and write accesses [TCSEC].

See register.

Pertaining to communications systems in which messages are received at intermediate routing points and recorded i.e., stored, and then transmitted, i.e., forwarded, to the next routing point or to the ultimate recipient.

A message switching center in which a message is accepted from the originating user, i.e., sender, when it is offered, held in a physical storage, and forwarded to the destination user, i.e., receiver, in accordance with the priority placed upon the message by the originating user and the availability of an outgoing channel.

A computer that (a) is controlled by internally stored instructions, (b) can synthesize and store instructions, and (c) can subsequently execute those instructions.

1. signal transfer point,
2. signaling transfer point,
3. spanning tree protocol.

See cross-connection.

The number of a clock (in a hierarchical synchronization distribution system) that defines the quality of the clock by specifying parameters such as frequency accuracy, pull-in range, and noise performance. The formal specifications are given in T1.101-1999 and T1.10
5. 09-199
7.
Note: Only stratum 1 clocks may operate independently; other clocks are slaved directly or indirectly to a stratum… (Read More →)

Electrical current through a path other than the intended path.

Synonym streaming tape drive.

A technique for transferring data (usually over the Internet) in a continuous flow to allow large multimedia files to be viewed before the entire file has been downloaded to a client's computer. [After Bahorsky]

Transmitted video or audio data that are viewed (or listened to) in real time, i.e., as the information is received. Streaming media may be user-controlled (as in on-demand, pay-per-view movies) or server-controlled (as in Webcasting).

A magnetic tape unit capable of recording from, and dumping to, another storage medium without stopping at interblock gaps.
Note: Streaming tape drives are often used for bulk transfer of data between tape and disk storage. Synonym streamer.

A method of recording on magnetic tape, which method maintains continuous tape motion without the requirement to start and stop within the interrecord gap.

Any component of a communication cable, metallic or optical, the function of which is to protect the transport medium, i.e., conductor or fiber, from excessive tensile and bending stresses during installation and while in service. [After FAA]

1. A measure of the effectiveness of a security mechanism to prevent a breach of the System Security policy, assuming it has been correctly implemented [CESG].
2. An aspect of the assessment of the effectiveness of a Target of Evaluation, namely the ability of its security mechanisms to withstand direct attack against deficiencies in their underlying algorithms, principles and properties… (Read More →)

In radiocommunications, an environment that is under the influence of extrinsic factors that degrade communications integrity, such as when (a) the benign communications medium is disturbed by natural or man-made events (such as an intentional nuclear burst), (b) the received signal is degraded by natural or man-made interference (such as jamming signals or co-channel interference), (c) an interfering signal can… (Read More →)

A sequence of data elements, such as bits or characters, considered as a whole.

A straight line or arc that is used as a segment of a graphic character.

In character recognition, the line of discontinuity between a side of a stroke and the background, obtained by averaging, over the length of the stroke, the irregularities resulting from the printing and detecting processes.

In facsimile systems, the rate at which a fixed line perpendicular to the direction of scanning is crossed in one direction by a scanning or recording spot.
Note 1: Stroke speed is usually expressed as a number of strokes per minute. When the system scans in both directions, the stroke speed is twice this number.
Note 2: In most conventional… (Read More →)

In character recognition, the distance between the two edges of a stroke, measured perpendicular to the stroke centerline.

Authentication by means of cryptographically derived credentials. [After X.509]

Development of a system or part of a system where components at lower levels are traceable from those at the higher level [CESG]. See also: Disciplined, Rigorous, Verified Development

A technique for organizing and coding computer programs in which a hierarchy of modules is used, each having a single entry and a single exit point, and in which control is passed downward through the structure without unconditional branches to higher levels of the structure. Three types of control flow are used: sequential, test, and iteration.

Text for which a well-defined, unambiguous internal structure is defined. Such text shall be human readable and interpreted identically by all conforming implementations [POSIX.6].

Acronym for secure telephone unit. A U. S. Government-approved telecommunications terminal that protects the transmission of sensitive or classified information in voice, data, and facsimile systems.

A network that conveys data only among local hosts.
Note: Even if the local hosts are connected to more than one other network, these hosts do not carry traffic between these other networks. [2382-pt.35]

A communications link used for the transmission of broadcast material from a studio to the transmitter.
Note: The STL may be a microwave, radio, or landline link.

See bit stuffing, de-stuffing.

Simple Traversal of UDP over NATs

A device that controls the nonprinting functions of a printer at a terminal.

Abbreviation for start-of-text character.

Acronym for substitute character.

Modulation in which (a) an audio frequency band is split into two sub-bands, i.e., a higher and a lower band, and (b) the signals in each sub-band are encoded using ADPCM.

[An] Individual with primary responsibility for managing the distinguished name process. [INFOSEC-99]

[A] major subdivision of an assembly consisting of a package of parts, elements, and circuits that perform a specific function. [INFOSEC-99]

A carrier used to modulate another carrier.
Note: The modulated carrier can be used to modulate another carrier, and so on, so that there can be several levels of subcarriers, i.e., several intermediate carriers.

A class derived from another class by specialization. [T1.260-1998]

1. In cryptography, an entity whose public key is certified in a public key certificate.
2. Generally, a person, process, or device, causing information to flow among objects or change to the system state. [INFOSEC-99]
3. An active entity, generally in the form of a person, process, executing program or device that causes information to flow among objects or changes… (Read More →)

An authority recognized in a Security Domain as a trusted source of security information concerning security subjects (human beings and Applications) [ECMA138].

Sensitivity label(s) of the objects to which the subject has both read and write access. Security level of a subject must always be dominated by the clearance level of the user associated with the subject. [INFOSEC-99]

1. In a layered open communications system, a specified subset of the services, functions, and protocols included in a given layer.
2. In the Open Systems Interconnection--Reference Model, a subdivision of a given layer, e.g., a conceptually complete group of the services, functions, and protocols included in the given layer.

In an Internet Protocol (IP) address, an extension that allows users in a network to use a single IP network address for multiple physical subnetworks.
Note: The IP address contains three parts: the network, the subnet, and host addresses. Inside the subnetwork, gateways and hosts divide the local portion of the IP address into a subnet address and a host… (Read More →)

A number that is used to identify a subnetwork so that IP addresses can be shared on a local area network.

1. A collection of equipment and physical transmission media that forms an autonomous whole and that can be used to interconnect systems for purposes of communication.
2. Specifically, a collection of open system interconnection (OSI) end systems and intermediate systems under the control of a single administrative domain and using a single network access protocol.
Note: Examples of subnetworks are… (Read More →)

Synonym slave station.

A set of computer instructions (or pieces of code) that run within a program (or are called within a program) to carry out a predefined function or computation.
Note: "Open" subroutines are integrated into the main program. "Closed" subroutines are arranged so that program control is shifted to them for execution of their task(s) and then returned to the main… (Read More →)

In computer conferencing, to add one's address to a distribution list, or to join a forum. [2382-pt.35]

1. In a public switched telecommunications network, the ultimate user, i.e., customer, of a communications service.
Note 1: Subscribers include individuals, activities, organizations, etc.
Note 2: Subscribers use end instruments, such as telephones, modems, facsimile machines, computers, and remote terminals, that are connected to a central office.
Note 3: Subscribers are usually subject to tariff.
Note 4: Subscribers do not… (Read More →)

See subscriber key.

A key encrypting key or data key transported in a multiple center CSM for eventual distribution to a pair of subscribers. [After X9.28]

1. Synonym loop.
2. A communication channel between a telephone station, PBX or TWX station and the central office which serves it. Synonym exchange line. [47 CFR Pt.36-A]

A subset of the carrier master database that is representative for a given user containing information related to the user, the user’s domain and the user’s subscriptions to services.

A mapping of a set of IPTV services to Devices and Users within a given consumer domain.

A control character that is used in the place of a character that is recognized to be invalid or in error or that cannot be represented on a given device.

In optical fiber technology, a method of measuring the transmission loss by (a) using a stable optical source, at the wavelength of interest, to drive a mode scrambler, the output of which overfills (drives) a 1-meter to 2-meter reference fiber having physical and optical characteristics matching those of the fiber under test, (b) measuring the power level at the output… (Read More →)

A class of tributary office which does not have direct access to its toll center, but which is connected to its toll center office by means of circuits which are switched through to the toll center at another tributary office. [47 CFR Pt.36-A]

A channel with a bandwidth narrower than that of a voice-grade channel.
Note: A subvoice-grade channel is usually a subchannel of a voice-grade line.

The transfer of a nonduplicate user information block between the source user and intended destination user.
Note: Successful block delivery includes the delivery of correct and incorrect blocks.

The transfer of a correct, nonduplicate, user information block between the source user and intended destination user.
Note: Successful block transfer occurs when the last bit of the transferred block crosses the functional interface between the telecommunications system and the intended destination user. Successful block transfer can only occur within a defined maximum block transfer time after initiation of a… (Read More →)

The termination of user information transfer between a source user and a destination user in response to a disengagement request.
Note: Successful disengagement occurs at the earliest moment at which either user is able to initiate a new information transfer transaction.

An abnormally high ionization density in the D region caused by an occasional sudden solar flare, i.e., outburst of ultraviolet light from the Sun.
Note: The SID results in a sudden increase in radio-wave absorption that is most severe in the upper medium-frequency (MF) and lower high-frequency (HF) ranges.

An aspect of the assessment of the effectiveness of a Target of Evaluation, namely the suitability of its security enforcing functions and mechanisms to in fact counter the threats to the security of the Target of Evaluation identified in its security target [ITSEC].

Synonym summation check.

1. A check based on the formation of the sum of the digits of a numeral.
Note: The sum of the individual digits is usually compared with a previously computed value.
2. A comparison of checksums on the same data on different occasions or on different representations of the data in order to verify data integrity. Synonym sum check.

In the photosphere, i.e., visible disk of the Sun, a dark marking that manifests a magnetic anomaly that is associated with interference with radio communications on Earth.
Note: Sunspot activity, i.e., the number of sunspots occurring at a given time or on a given day, is cyclic. The period of a cycle, from maximum through minimum and back to maximum… (Read More →)

See electromagnetic spectrum.

A class used in deriving another class by specialization. [T1.260-1998]

[The] process of encrypting encrypted information.
Note: [This process] occurs when a message, encrypted off-line, is transmitted over a secured, on-line circuit, or when information encrypted by the originator is multiplexed into a communications trunk, which is then bulk encrypted. [INFOSEC-99]

1. In T-carrier, a synchronization frame that delineates 12 DS1 frames. [J. Beaty, FAA]
2. A DS1 framing format that assembles 12 individual DS1 frames into a single superframe with a 12-bit fixed frame pattern. [T
1. Rpt25-1993]

See group, multiplex hierarchy.

In frequency-division multiplexing (FDM), the distribution frame that provides terminating and interconnecting facilities for group modulator output, group demodulator input, supergroup modulator input, and supergroup demodulator output circuits of the basic supergroup spectrum of 312 kHz to 552 kHz.

See National Information Infrastructure.

A light-emitting diode in which there is stimulated emission with amplification but insufficient feedback for oscillations to build up to achieve lasing action.

In a gain medium, amplification of spontaneously emitted radiation characterized by moderate spectral line narrowing and moderate directionality.
Note: Superradiance is usually distinguished from lasing action by the absence of positive feedback, and hence the absence of well-defined modes of oscillation.

An oversized sector written on a diskette, as part of a method of copy protection. [2382-pt.8]

[In security,] scheduled or unscheduled replacement of a COMSEC aid with a different edition. [INFOSEC-99]

1. [A] special user who can perform control of processes, devices, networks, and file systems. [INFOSEC-99]
2. An informal name for root.

Synonym supervisory program.

Synonym executive state.

The use of characters or signals for the automatic actuation of equipment or indicators.

1. A program, usually part of an operating system, that controls the execution of other routines and regulates work scheduling, input-output operations, error actions, and similar functions.
2. A program that allocates computer component space and schedules computer events by task queuing and system interrupts.
Note: Control of the system is returned to the supervisory program frequently enough to ensure… (Read More →)

Synonym supervisory program.

Specific electrical conditions (called "on-hook" and "off-hook") at the NI (network interface) that are used to control call states and processes. [T1.414-1998]

Signals used to indicate, or to indicate and control, the various operating states of the circuits or circuit combinations involved in a particular connection.

Secure User Plane Location

The provision of coverage to terrestrial wireless subscribers through an arrangement or agreement (see §
1. 9047 of this chapter) between one or more NGSO or GSO operator(s) and one or more terrestrial wireless licensee(s), involving transmissions between space stations and SCS earth stations. NGSO and GSO operators and terrestrial wireless service licensees seeking to provide SCS must be authorized… (Read More →)

Specific type of application that provides security services or security management capabilities at application level rather than embedded in the communication architecture [ECMATR46].

A single-sideband emission in which the carrier is virtually suppressed and not intended to be used for demodulation. [NTIA] [RR]

Amplitude modulation (AM) transmission in which the carrier level is reduced below that required for demodulation.
Note 1: Reduction of the carrier level permits higher power levels in the sidebands than would be possible with conventional AM transmission.
Note 2: Carrier power must be restored by the receiving station to permit demodulation.
Note 3: Suppressed carrier transmission is a special… (Read More →)

[An] Action, procedure, modification, or device that reduces the level of, or inhibits the generation of, compromising emanations in an information system (IS). [INFOSEC-99]

Slang. To search the Web, by navigating in a nonlinear and seemingly random way, often without a specific objective.

The refractive index of the Earth's atmosphere, calculated from observations of pressure, temperature, and humidity at the surface of the Earth.
Note: The surface refractivity gradient is the difference in refractive index between the surface and a given altitude, such as between the surface and 1000 m.

A wave that is guided along the interface between two different media or by a refractive index gradient.
Note 1: The field components of the wave diminish with distance from the interface.
Note 2: Optical energy is not converted from the surface wave field to another form of energy and the wave does not have a component directed normal to… (Read More →)

Synonym impulse.

An assembly of one or more components intended to limit or divert surges; the device contains at least one nonlinear component. [T1.321-1995] Synonyms arrester, surge protector.

Synonyms arrester, surge protective device, surge protector.

See discretionary access control.

1. The use of (usually) electronic means, passive or active, to obtain information about the nature, position, or movement of, e.g., aircraft (cooperative or non-cooperative, friendly or unfriendly), sources of electromagnetic emissions, etc.
2. Nonintrusive monitoring of digital signals in real time to recognize performance degradations and failures and system intrusion attempts. [After T1.231-1997]

See path survey.

A property of a system, subsystem, equipment, process, or procedure that provides a defined degree of assurance that the named entity will continue to function during and after a natural or man-made disturbance; e.g., nuclear burst.
Note: For a given application, survivability must be qualified by specifying the range of conditions over which the entity will survive, the minimum acceptable… (Read More →)

See survivability.

A mobile station in the maritime mobile service or the aeronautical mobile service intended solely for survival purposes and located on any lifeboat, life-raft or other survival equipment. [NTIA] [RR]

In electronic warfare, the degree to which electronic equipment is affected by electromagnetic energy radiated by an enemy's equipment, such as jamming transmitters.

1. The amount of undesired signal power required at the input terminals of a receiver to cause barely perceptible interference at the receiver output terminals.
2. In cryptology, the level above which a system has the ability to continue to process critical applications in spite of the fact that it has suffered disruptive or damaging effects (such as contamination with… (Read More →)

In telephone systems, the extent to which circuits pick up noise and low-frequency energy by induction from power systems.
Note: Susceptiveness depends on telephone circuit balance, wire and connection transpositions, wire spacing, and isolation from ground.

Subscription Video On Demand

Software

A technique whereby the frequency of the local oscillator is slowly swept past the reference in order to assure that the pull-in range is reached.

Jamming in which (a) a narrow frequency band of jamming energy is repeatedly swept over a relatively wide frequency band, (b) the sweep rate is such as to be on any given frequency only long enough to accomplish its jamming task, returning to that frequency again before the expiration of the jammed circuit recovery time.
Note 1: Sweep jamming combines… (Read More →)

Slow, graceful, undesired movements of display elements, groups, or images about their mean position on a display surface, such as that of a monitor.
Note 1: Swim can be followed by the human eye, whereas jitter usually appears as a blur.
Note 2: Jitter, swim, wander, and drift have increasing periods of variation in that order.

1. In communications systems, a mechanical, electro-mechanical, or electronic device for making, breaking, or changing the connections in or among circuits.
2. Deprecated synonym for central office, switching center.
3. In communications systems, to transfer a connection from one circuit to another.
4. In a computer program, a conditional instruction and a flag that is interrogated by the instruction.
5.… (Read More →)

In telephony, the busy hour for a single switch.

Equipment used for manual switching operations.

A communication path between local exchange and a customer interface (CI). [T1.401-1988]

In a communications network, a circuit that may be temporarily established at the request of one or more of the connected stations.

See switched circuit.

Describes acceptance testing procedures used when Switched Access Services are provided with a digital switch on digital facilities.

The network of switching systems, interconnecting facilities, and equipment provided by an exchange carrier (EC) to provide telecommunications services between the exchange office (EO) and interexchange carrier point of termination (IC-POT). [T1.508-1998]

In telephony, a circuit that automatically releases a connection from a console or switchboard, once the connection has been made to the appropriate terminal.
Note: Loop buttons or jacks are used to answer incoming listed directory number calls, dial "0" internal calls, transfer requests, and intercepted calls. The attendant can handle only one call at a time. Synonym released loop.

A connectionless, broadband, packet-switched data service that provides LAN-like performance and features in metropolitan or wide areas.
Note: Currently SMDS operates at
1. 544 Mb/s (megabits per second) or
4
4. 736 Mb/s. These are the T1 and T3 rates, respectively, over switched fiber optic networks.

1. A communications network, such as the public switched telephone network, in which any user may be connected to any other user through the use of message, circuit, or packet switching and control devices.
2. Any network providing switched communications service.

The controlling or routing of signals in circuits to execute logical or arithmetic operations or to transmit data between specific points in a network.
Note: Switching may be performed by electronic, optical, or electromechanical devices. [From Weik '89]

In communications systems, a facility in which switches are used to interconnect communications circuits on a circuit-, message-, or packet-switching basis. Synonyms, in telephony, central office, switching exchange, switching facility. Deprecated synonym yyswitch.

Synonym switching center.

Synonym switching center.

1. A communications system consisting of switching centers and their interconnecting media.
2. Part of a communication system organized to temporarily associate functional units, transmission channels or telecommunication circuits for the purpose of providing a desired telecommunication facility.
Note: Examples of NATO-owned switching systems are IVSN and TARE.

Synonym yyswitch.

Abbreviation for standing wave ratio.

Abbreviation for simplex signaling.

Abbreviation for step-by-step switching system.

[A] list of individual letters, combination of letters, or syllables, with their equivalent code groups, used for spelling out words or proper names not present in the vocabulary of a code. A syllabary may also be a spelling table. [INFOSEC-99]

A character string or a bit string in a word.

A computer programming language used to express addresses and instructions with symbols convenient to humans rather than to machines.

The discipline in which valid arguments and operations are dealt with using an artificial language designed to avoid the ambiguities and logical inadequacies of natural languages.

Method for demonstrating knowledge of a secret, in which both entities share a common authentication information [10181-2].

Cryptography in which the same key is used for encryption and decryption. [2382-pt.8]

A channel in which the send and receive circuits have the same data signaling rate.

A balanced transmission line, in a multipair cable, having equal conductor resistances per unit length, equal impedances from each conductor to earth, and equal impedances to other lines.

The attribute describing the relationship of information flow between two (or more) access points or reference points involved in a communication. Symmetry characterizes the structure associated with a telecommunication service or a connection. Values associated with this attribute are unidirectional, bidirectional symmetric, and bidirectional asymmetric. [After T1.603-1990] [After T1.604-1990]

Acronym for synchronous idle character.

ATIS Synchronization Committee

Synonym synchronization pulse.

1. The state of being synchronous.
2. For repetitive events with the same, multiple, or submultiple repetition rates, a relationship among the events such that a significant instant of one event bears a fixed time relationship to a corresponding instant in another event.
Note: Synchronism is maintained when there is a fixed, i.e., constant, phase relationship among the group of… (Read More →)

1. The attaining of synchronism between the frequencies or between the frequencies and phases of two or more signals. [T
1. X1]
2. The obtaining of a desired fixed relationship among corresponding significant instants of two or more signals. [T
1. X1]
3. A state of simultaneous occurrences of significant instants among two or more signals. [T
1. X1]

A bit used to achieve or maintain synchronism.
Note: The term "synchronization bit" is usually applied to digital data streams, whereas the term "synchronization pulse" is usually applied to analog signals.

In digital systems, a sequence of bits introduced into a transmitted signal to achieve or maintain synchronism.

A pulse used to achieve or maintain synchronism.
Note: The term "synchronization pulse" is usually applied to analog signals, whereas the term "synchronization bit" is usually applied to digital data streams. Synonym sync pulse.

1. Achieving and maintaining synchronism.
2. In facsimile, achieving and maintaining predetermined speed relations between the scanning spot and the recording spot within each scanning line.
Note: In the civilian community, the noun "synchronization" is preferred to "synchronizing. "

In FDM, a reference frequency used for achieving and maintaining syntonization of the oscillators of a carrier system or for comparing the frequencies or phases of the signals generated by those oscillators.

In facsimile systems, the signal that maintains predetermined speed relations between the scanning spot and recording spot within each facsimile scanning line.

1. Pertaining to the relationship of two or more repetitive signals that have simultaneous occurrences of significant instants.
Note: "Isochronous" and "anisochronous" pertain to characteristics. "Synchronous" and "asynchronous" pertain to relationships.
2. Pertaining to synchronism.

[A] method of on-line crypto-operation in which crypto-equipment and associated terminals have timing systems to keep them in step. [INFOSEC-99]

In a data network, a bit-oriented protocol for the control of synchronous transmission over data links.

A data network in which synchronism is achieved and maintained between data circuit-terminating equipment (DCE) and the data switching exchange (DSE), and between DSEs.
Note: The data signaling rates are controlled by timing equipment within the network.

See synchronous orbit.

A transmission control character used in synchronous transmission systems to provide a signal from which synchronism or synchronous correction may be achieved between data terminal equipment, particularly when no other character is being transmitted.

1. A network in which clocks are controlled to run, ideally, at identical rates, or at the same mean rate with a fixed relative phase displacement, within a specified limited range.
Note: Ideally, the clocks are synchronous, but they may be mesochronous in practice. By common usage, such mesochronous networks are frequently described as "synchronous. "
2. A network in… (Read More →)

See SONET.

Any orbit in which an orbiting object has a period equal to the average rotational period of the body being orbited, and in the same direction of rotation as that body.
Note 1: A synchronous orbit need not be equatorial, but it usually is, ideally. A body in a nonequatorial synchronous orbit will, when observed from a fixed point on… (Read More →)

Payloads derivable from a network transmission signal by removing integral numbers of bits in every frame, i.e., there are no variable bit stuffing rate adjustments required to fit the payload in the transmission signal. [T1.105-1988]

A satellite in a synchronous orbit.

A system in which events, such as signals, occur in synchronism.
Note 1: An example of a synchronous system is one in which a transmitter and receiver operate with a fixed time relationship.
Note 2: A second example is SONET, which may accommodate payload signals in channels that are clocked at submultiples of the carrier clocking rate. [T
1. X1]

A transcoding of the form ADPCM-PCM-ADPCM (adaptive differential pulse code modulation-pulse code modulation-adaptive differential pulse code modulation) when there are no transmission errors and the integrity of the bit stream is preserved. [T1.310-1991]

A multiplexing scheme in which timing is obtained from a clock that controls both the multiplexer and the channel source.

The term "Synchronous Test Line" denotes an arrangement in an end office which performs marginal operational tests of supervisory and ring-tripping functions.

In a Broadband Integrated Services Digital Network (B-ISDN), a proposed transport level technique in which time-division multiplexing and switching is to be used across the user's network interface.

Digital transmission in which the time interval between any two similar significant instants in the overall bit stream is always an integral number of unit intervals.
Note: "Isochronous" and "anisochronous" are characteristics, while "synchronous" and "asynchronous" pertain to relationships.

The basic logical building block signal of synchronous optical networks (SONET). The STS-1 signal has a bit rate of
5
1. 840 Mb/s. [T
1. X1] [After T1.105-1988]

1. In a language, the relationships among characters or groups of characters, independent of their meanings or the manner of their interpretation and use.
2. The structure of expressions in a language.
3. The rules governing the structure of a language.
4. In a language, the relationship among symbols.
Note: In computer languages, as in all artificial languages, syntax is… (Read More →)

The process of setting the frequency of one oscillator equal to that of another.
Note: The term "synchronization" is commonly used in place of "syntonization" to mean the same thing. [T
1. X1]

Acronym for system generation.

1. Acronym for system(s) operator.
1. The person responsible for performing the day-to-day and periodic maintenance of a computer forum.
2. An individual responsible for the physical operations of a network or of a computer system. [After Bahorsky]

1. Any organized assembly of resources and procedures united and regulated by interaction or interdependence to accomplish a set of specific functions. [JP 1-02]
2. A combination of two or more interrelated equipment (sets) arranged in a functional package to perform an operational function or to satisfy a requirement. [JP 1-02]
3. A collection of personnel, equipment, and methods organized… (Read More →)

In computer technology, a set of functions that provides support services, ensures reliable operations, promotes efficient use of the system, and ensures that prescribed service-quality objectives are met. Synonym system management.

The person responsible to the System Manager for the day-to-day operation of a system. vSee also: System Security officer [CESG].

A systematic investigation of a real or planned system to determine the functions of the system and how they relate to each other and to any other system. Synonym systems analysis.

Synonym access denial.

A control message generated within a telecommunications system to indicate temporary unavailability of system resources required to complete a requested access.
Note: The system blocking signal is part of system overhead information.

See power budget.

The identification of the boundaries of a system to establish a firm basis for any interconnection with other systems [CESG].

The collection of documents that describes the requirements, capabilities, limitations, design, operation, and maintenance of a system, such as a communications, computing, or information processing system.

A detailed statement of the technical aspects of a System Security Policy [CESG].
Note: A System Electronic Information Security Policy provides the baseline for evaluation.

In the event of a catastrophic failure, the ability to transfer central office trunks or interoffice trunking to predetermined stations to allow incoming and outgoing calls to be completed.

The study of the effects of a system after it has reached a stabilized state of operational use. Synonyms post-development review, post-implementation review.

The process of selecting optional parts of an operating system and of creating a particular operating system tailored to the requirements of a data processing installation.

1. [An] information system (IS) security mode of operation wherein each user, with direct or indirect access to the information system (IS), its peripherals, remote terminals, or remote hosts, has all of the following: (a) valid security clearance for all information within an IS; (b) formal access approval and signed nondisclosure agreements for all the information stored and/or processed (including… (Read More →)

[A] symbol or group of symbols in an off-line encrypted message identifying the specific cryptosystem or key used in the encryption. [INFOSEC-99]

The progressive linking and testing of system components to merge their functional and technical characteristics into a comprehensive, interoperable system.
Note: Integration of data systems allows data existing on disparate systems to be shared or accessed across functional or system boundaries.

1. That condition of a system wherein its mandated operational and technical parameters are within the prescribed limits.
2. [The] Attribute of an information system (IS) when it performs its intended function in an unimpaired manner, free from deliberate or inadvertent unauthorized manipulation of the system. [INFOSEC-99]

A bilateral memorandum of agreement between two System Managers on the security aspects of an interconnection between their two systems [CESG]. See also: Community Security Policy.

The interface between application platform service components within that platform; it may be standardized or non-standard [POSIX.0].

A key used to provide privacy to an encrypted object as it transits a communications network. [After X9.69]

The course of developmental changes through which a system passes from its conception to the termination of its use and subsequent salvage.
Note: For example, a system life cycle might include the phases and activities associated with the analysis, acquisition, design, development, test, integration, operation, maintenance, and modification of the system.

In a frequency-division multiplexed (FDM) transmission system, the absolute power level of the composite signal transmitted in one direction.
Note 1: The absolute power level is referred to a zero transmission level point (0TLP).
Note 2: The composite signal contains signaling, speech, and digital signals.

1. Network management functions extended to include subscriber elements or user end instruments.
2. In computer systems, synonym system administration.

The person ultimately responsible for the production and enforcement of a System Security Policy [CESG]. See also: System Administrator, System Security Officer.

For a supported performance parameter of a system, the value that establishes the minimum operational service performance level for the parameter.
Note: A measured parameter value worse than the system operational threshold indicates that the system is in an outage state.

See overhead information.

Synonym power margin.

[In INFOSEC, the] detailed security description of the physical structure, equipment component, location, relationships, and general operating environment of an information system (IS). [INFOSEC-99]

The probability that a system, including all hardware, firmware, and software, will satisfactorily perform the task for which it was designed or intended, for a specified time and in a specified environment. [From Weik '89]

The measure or extent of the ability of a system, such as a computer, communications, data processing, or weapons system, to continue to function despite the existence of faults in its component subsystems or parts.
Note: System performance may be diminished or otherwise altered until the faults are corrected.

[In INFOSEC, the] degree of security as determined by evaluation of the totality of all system elements and INFOSEC countermeasures. [INFOSEC-99]

The effort to achieve and maintain optimal security and survivability of a system throughout its life cycle. [INFOSEC-99]

Risk assessment of a system, considering its vulnerabilities and perceived security threat. [INFOSEC-99]

The person responsible to the System Manager for writing, enforcing and reviewing Security Operating Procedures (SyOPs) [CESG].

1. The set of laws, rules and practices that regulate how sensitive information and other resources are managed, protected and distributed within a specific system [ITSEC].
2. [CESG]. A statement by a System Manager/Project Manager defining a system, its Security Requirement, the security measures to be enforced and the allocation of responsibilities for enforcing them. [CESG].
Note: When an SEISP… (Read More →)

Firmware and software that provide an aggregation of network element functions into a higher level function; provide an interface to the data contained in the system [POSIX.0].

An interface providing access to services associated with the application's internal resources [POSIX.0].

In transmission systems, any scheme used to provide such functions as system control, addressing, routing, error detection and correction, level control, priority, traffic control, message accountability, and/or other required overhead information.

1. Application-independent software that supports the running of application software.
2. Application-independent software that supports the running of application software and manages the resources of the application platform [POSIX.0].

In the military community, the system-specific characteristics, not dictated by the individual components' electrical performance characteristics, but necessary in order to permit internal and external interoperability.

In telephone systems, the use of signals and techniques to perform system management functions, such as system control, addressing, routing, error detection and correction, level control, priority, traffic control, message accountability, and other overhead functions that may be described in system overhead portions of messages. [From Weik '89]

The continued provision of services and material necessary for the use and improvement of a system during its life cycle.

The part of operating time during which a functional unit is tested for proper operation.
Note: In a computer, the system test time may include the time for testing programs belonging to the operating system.

Synonym system analysis.

In a communications system, the control and implementation of a set of functions that (a) prevent or eliminate degradation of any part of the system, (b) initiate immediate response to demands that are placed on the system, (c) respond to changes in the system to meet long range requirements, and (d) may include various subfunctions, such as (i) immediate circuit… (Read More →)

1. A process of defining the hardware and software architecture, components, modules, interfaces, and data for a system to satisfy specified requirements.
2. The preparation of an assembly of methods, procedures, or techniques united by regulated interaction to form an organized whole. [JP1]

See systems design.