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January 27, 20142 min read

A Glossary of P25 Terminology — Part 1 (A to C)


APCO P25 Logo

Over the last few weeks, we have covered P25 radio communications in great detail, including An Introduction to P25, The P25 Standard and Compliance and Benefits of P25. As a recap and to tie everything in together, over the next few weeks we’ll present a glossary of all the P25 radio-related terms that you need to know.


AES (Advanced Encryption Standard) is an encryption algorithm that uses keys of 256 bits.

Algorithm ID
The Algorithm ID is an identifier that specifies an encryption algorithm (for example, DES or AES).

The Association of Public Safety Communications Officials in the United States. The APCO Project 25 standards committee defined the P25 digital radio standard. The standard is often referred to as APCO or P25.


Base Station
A radio receiver and transmitter that is located in a specific place (at a site) that enables a two-way radio to communicate with a dispatcher or over a larger range with other two-way radios.

Bit Error Rate. A measure of the quality of a digital transmission, expressed as a percentage. The BER indicates the proportion of errors to correctly received digits in a received signal.


Compatible Four-level Frequency Modulation. A modulation scheme defined in the P25 CAI standard for 12.5 kHz bandwidth.

Common Air Interface. The over-the-air data formats and protocols defined by the APCO P25 committee.

Channel Group
A channel group is a Tait term for a single logical channel consisting of a set of base stations. Console gateways can also be members. The members of a channel group are linked by an IP network and share a common multicast IP address.

Channel Spacing
Channel spacing is the bandwidth that a channel nominally occupies. If a base station has a channel spacing of 12.5 kHz, there must be a separation of at least 12.5 kHz between its operating frequencies and those of any other equipment.

The CKR (common key reference) is a number used by the key fill device and by the CSS to indirectly refer to an encryption key without using its Key ID or Algorithm ID.

Conventional Network
Conventional networks are systems that do not have centralized management of channel access. System operation is entirely controlled by system end users.

Crypto Module
Module for securely storing encryption keys and for encrypting and decrypting signals.

Customer Service Software. Tait PC-based software for monitoring, configuring, and diagnosing an Tait Generic base station or gateway.

Console SubSystem Interface. The communication interface used to connect a trunked analog gateway to the RFSS controller.

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