See Open Systems Interconnection--Reference Model.

The smallest convenient division of a media stream (defined by the measurement system) that conveys an independent, self-contained unit of content, from among the content hierarchy levels present in the stream. [T1.80
1. 04-1997]

A service feature that permits the automatic connection of a fixed group of users, or a closed user group with outgoing access, by keying a single directory number. [From Weik '89]

A jammer in which the frequency of the jamming transmitter is fixed before the transmitter is placed in operation.
Note: Preset jammers are most useful in airborne jamming operations where weight and space requirements may prohibit the use of operators or elaborate control equipment in flight. Preset jammers are usually used in barrage-jamming over a wide band, usually in overlapping… (Read More →)

Synonym push-to-talk operation.

Synonym push-to-type operation.

1. The care and servicing by personnel for the purpose of maintaining equipment and facilities in satisfactory operating condition by providing for systematic inspection, detection, and correction of incipient failures either before they occur or before they develop into major defects. [JP1]
2. Maintenance, including tests, measurements, adjustments, and parts replacement, performed specifically to prevent faults from occurring.

Abbreviation for pulse repetition frequency.

Abbreviation for primary rate interface.

1. The channel that is designated as a prime transmission channel and is used as the first choice in restoring priority circuits.
2. In a communications network, the channel that has the highest data rate of all the channels sharing a common interface.
Note: A primary channel may support the transfer of information in one direction only, either direction alternately,… (Read More →)