Project 25

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Project 25 (P25) is a suite of standards for digital radio communications for use by federal, state/province and local public safety agencies in North America to enable them to communicate with other agencies and mutual aid response teams in emergencies. In this regard, P25 fills the same role as the European Tetra protocol, although not interoperable with it.

1 Suite of Standards Overview
- 1.1 P25 Open Interfaces
- 1.2 P25 Phases
2 Adoption
3 See also
4 External links

[edit] Suite of Standards Overview

Project 25 (P25) was established by joint efforts of the Association of Public Safety Communications Officials International (APCO), the National Association of State Telecommunications Directors (NASTD), selected Federal Agencies and the National Communications System (NCS). It was established to address the need for common digital public safety radio communications standards for First Responders and Homeland Security/Emergency Response professionals. TIA TR-8 facilitates such work through its role as an ANSI-accredited Standards Development Organization (SDO).

The P25 suite of standards involves digital Land Mobile Radio (LMR) services for local, state and national (federal) public safety organizations and agencies. P25 is applicable to LMR equipment authorized or licensed, in the U.S., under the National Telecommunications and Information Administration (NTIA) or Federal Communications Commission (FCC) rules and regulations. However, use of such equipment is not limited to public safety, and P25 equipment has also been selected and deployed in other private system applications, for example, to serve the needs for a high-quality, secure digital radio system for a railroad system, including rolling stock, personnel, and transportation vehicles.

P25-compliant systems are being increasingly adopted and deployed. Radios can communicate in analog mode with legacy radios, and in either digital or analog mode with other P25 radios. Additionally, the deployment of P25-compliant systems will allow for a high degree of equipment interoperability and compatibility. Specifically, P25 systems can be maintained and upgraded cost effectively over the system's life cycle, thus meeting user requirements, achieving interoperability and security, promoting committed manufacturers to provide compliant products, fostering competition and achieving cost-effective emergency/safety communication solutions. In light of recent worldwide terrorist activities, interoperability among first responders is a key initiative of many countries.

P25 standards use the Improved Multiband Excitation IMBE vocoders which were designed by DVSI to encode/decode the analog audio signals.

P25 may be used in "talk around" mode without any intervening equipment between two radios, in "conventional" mode where two radios communicate through a repeater or base station without trunking or in a trunked mode where traffic is automatically assigned to one or more voice channels by a Repeater or Base Station.

The protocol supports the use of DES encryption (56 bit), 2-key Triple-DES encryption (112 bits), 3-key Triple-DES encryption (168-bits), AES encryption at up to 256 bits keylength, RC4 (40 bits, sold by Motorola as Advanced Digital Privacy), or no encryption.

The protocol also supports the ACCORDION 1.3, BATON, FIREFLY, MAYFLY and SAVILLE Type 1 ciphers.

[edit] P25 Open Interfaces

P25's Suite of Standards specify eight open interfaces between the various components of a land mobile radio system. These interfaces are:

Common Air Interface (CAI) standard specifies the type and content of signals transmitted by compliant radios. One radio using CAI should be able to communicate with any other CAI radio, regardless of manufacturer
Subscriber Data Peripheral Interface standard specifies the port through which mobiles and portables can connect to laptops or data networks
Fixed Station Interface standard specifies a set of mandatory messages supporting digital voice, data, encryption and telephone interconnect necessary for communication between a Fixed Station and P25 RF Subsystem
Console Subsystem Interface standard specifies the basic messaging to interface a console subsystem to a P25 RF Subsystem
Network Management Interface standard specifies a single network management scheme which will allow all network elements of the RF subsystem to be managed
Data Network Interface standard specifies the RF Subsystem's connections to computers, data networks, or external data sources
Telephone Interconnect Interface standard specifies the interface to Public Switched Telephone Network (PSTN) supporting both analog and ISDN telephone interfaces.
Inter RF Subsystem Interface (ISSI) standard specifies the interface between RF subsystems which will allow them to be connected into wide area networks

[edit] P25 Phases

P25-compliant technology is being deployed in several phases:

Phase I

Phase I radio systems operate in 12.5 kHz analog, digital or mixed mode. Phase I radios use Continuous 4 level FM (C4FM) modulation for digital transmissions at 4800 baud and 2 bits per symbol, yielding 9600 bits per second total channel throughput. Receivers designed for the C4FM standard can also demodulate the "Compatible quadrature phase shift keying" (CQPSK) standard, as the parameters of the CQPSK signal were chosen to yield the same signal deviation at symbol time as C4FM while using only 6.25 kHz of bandwidth.

Vendors are currently shipping Phase I P25-compliant systems. These systems involve standardized service and facility specifications, ensuring that any manufacturers' compliant subscriber radio has access to the services described in such specifications. Abilities include backward compatibility and interoperability with other systems, across system boundaries, and regardless of system infrastructure. In addition, the P25 suite of standards provides an open interface to the radio frequency (RF) subsystem to facilitate interlinking of different vendors' systems.

Phase II

To improve spectrum utilization, Phase II is currently under development with concurrent work being done on 2-slot TDMA and FDMA (CQPSK) modulation schemes. Phase II will use the AMBE vocoder to reduce the needed bitrate so that one channel will only require 4800 bits per second.

Significant attention is also paid to interoperability with legacy equipment, interfacing between repeaters and other subsystems, roaming capacity and spectral efficiency/channel reuse. In addition, Phase II work involves console interfacing between repeaters and other subsystems, and man-machine interfaces for console operators that would facilitate centralized training, equipment transitions and personnel movement.

[edit] Adoption

Adoption of these standards has been slowed by budget problems in the US, however funding for communications upgrades from the Department of Homeland Security usually requires migrating to APCO-25. It is also being used in other countries world wide.