A Glossary of P25 Terminology — Part 4 (S to Z)

APCO P25 LogoIn this last part of the P25 glossary, we cover squelch, simulcast, VoIP and many other essential P25 terms.

Previous posts in this series:
A Glossary of P25 Terminology — Part 1 (A to C)
A Glossary of P25 Terminology — Part 2 (D to K)
A Glossary of P25 Terminology — Part 3 (L to R)


Satellite Voter
A TaitNet channel group member that has delegated voting activity to a central voter.

The ability of a radio receiver to select the wanted signal and reject unwanted signals on adjacent channels (expressed as a ratio).

Selective Squelch
A type of squelch operation in which the receiver unmutes only on signals that are explicitly addressed to that receiver. This can be done through a talk group ID or unit ID (digital P25) or through MDC1200 signaling (analog FM).

The sensitivity of a radio receiver is the minimum input signal strength required to provide a usable signal.

Able to provide transmission and reception only in one direction at a time.

Simulcast is the simultaneous broadcast by more than one transmitter of the same signal on the same frequency.

Simple Network Management Protocol. A protocol used (for example) by the trunking site controller to monitor the status of the channel group and its members.

Squelch is a feature of radio equipment. It ensures that the speaker only unmutes when a valid signal is received. To be valid, it must, for example, have the correct NAC.

Abbreviation for subscriber unit. This is the term used in the APCO P25 standard documents for a two-way radio (generally a mobile or a portable radio) conforming to the CAI specifications.

Supplementary Service
A term used in the P25 standards. It refers to a group of services that is additional to the basic service that a telecommunications network provides. Examples include encryption and SU monitoring.

Syslog Protocol
Syslog is a standard protocol used for the transmission of event notification messages across IP networks. Base stations and gateways can send messages such as alarms to an IP address on the TaitNet P25 network. The base station’s logs store messages in the syslog format.

Syslog Collector
A program that can receive, display, and log syslog messages from many devices.

Brand name for a PMR network designed and manufactured by Tait.

Tait P25 network
A set of Tait base stations interconnected by an IP network that can carry voice and data traffic.

Task Manager
Task Manager is a part of the Tait TB9100 network element firmware that carries out tasks in response to inputs. These tasks are formulated using the CSS.

Telecommunications Industry Association

A TSBK (trunking signaling block) is an over-the-air message format used in digital P25 mode for setting up trunked calls and for supplementary services such as messaging and status updates.

A control command that can be sent across the CAI to restore an inhibited SU to normal functioning.

Coordinated Universal Time (word order from French). An international time standard that has replaced Greenwich Mean Time.

Voice encoder/decoder. A processing element that compresses/decompresses the digital voice signal.

Voice over IP. The name for the technology that puts speech signals in packets and then routes them over an IP backbone network.

Voting is the systematic sampling of a group of channels for the channel with the greatest signal strength. Voting provides wide-area coverage and ensures that as the user moves throughout the coverage area the strongest channel is always available for a call.

Voltage Standing Wave Ratio (VSWR) is the ratio of the maximum peak voltage anywhere on the transmission line to the minimum value anywhere on the transmission line. A perfectly matched line has a VSWR of 1:1. A high ratio indicates that the antenna subsystem is poorly matched.

Wide Area Network.

To zeroize one or more encryption keys is to render them useless by overwriting the key data with zeros.

If you feel we have missed any important P25 term in the glossary, please let us know in the comments below.

We have recently released a set of guides that cover P25 Best Practice for specifying, procuring and implementing a P25 radio system. You can either browse the P25 Best Practice website or download the P25 guides in PDF format for free.

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