The deflection--by diffraction, nonhomogeneous refraction, or nonspecular reflection by particulate matter of dimensions that are large with respect to the wavelength in question but small with respect to the beam diameter--of a portion of an incident electromagnetic wave, in such a manner that the energy so deflected propagates in a direction that is within 90° of the direction of propagation… (Read More →)

The confidence that the compromise of a long-term private key does not compromise any earlier session keys. [After X9.42]

A field in a signal unit used to identify the transmitted message signal units. [T1.226-1992]

A signal sent in the direction from the calling to the called station, i.e., from the original data source to the original data sink.
Note: The forward signal is transmitted in the forward channel.

1. Frequency of Optimum Transmission,
2. Frequency of Optimum Traffic,
3. Fiber Optic Terminals.

A two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path.
Note: The four-wire circuit gets its name from the fact that, historically, two conductors were used in each of two directions for full-duplex operation. The name may still be applied,… (Read More →)

A repeater, consisting of two amplifiers, one associated with each direction, used in a four-wire circuit.

A balanced transformer used to perform a conversion between 4-wire and 2-wire operation.
Note 1: For example, a 4-wire circuit may, by means of a 4-wire terminating set, be connected to a 2-wire telephone set. Also, a pair of 4-wire terminating sets may be used to introduce an intermediate 4-wire loop into a 2-wire circuit, in which loop repeaters may… (Read More →)

The definition of a periodic waveform of arbitrary shape as a summation of sine waves having specific amplitudes and phases, and having frequencies corresponding to the harmonics of the waveform being defined.
Note: A Fourier analysis is particularly well suited for communications equipment design and for predicting the performance of a given design. [From Weik '89]

A standard test message that includes all the alphanumerics on a teletypewriter and also function characteristics (yyspace, figures shift, letters shift).
Note: An example of a fox message is "THE QUICK BROWN FOX JUMPED OVER THE LAZY DOG'S BACK
123456789
0. "