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.