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Project 25 (P25) is a set of standards produced through the 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), and standardized under the Telecommunications Industry Association (TIA). P25 was established to address the need for common digital public safety radio communications standards for First Responders and Homeland Security/Emergency Response professionals.
|Overview of P25 MOBILE Radios
Although developed primarily for North American public safety services, P25 technology and products are not limited to public safety alone and have also been selected and deployed in other private system application, worldwide.
The 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/provincial and national (federal) public safety organizations and agencies. It has been widely adopted in the United States. The standard allows radios from different manufacturers to work with each other.
|P25 Deployment, Interoperbility
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. 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. P25 supports trunking or conventional traffic by a Repeater or Base Station.
Like all Standards, the quality of the interoperability depends on how well they follow the standard. P25 does do voluntary certification through organization. Any P25 equipment you may want to buy needs to be certified. 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.
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. AES Encryption is the most commonly supported. The protocol also supports the ACCORDION 1.3, BATON, FIREFLY, MAYFLY and SAVILLE Type 1 ciphers although these are not widely supported by the manufacturers.
P25 also supports data applications such as GPS. Other features include OTAR (over the air rekeying for Encryption) and OTAP (Over the Air Reprogramming)
P25's Suite of Standards specify eight open interfaces between the various components of a land mobile radio system. These interfaces are:
Vendors are currently shipping Phase 1 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.
To improve spectrum utilization, Phase 2 is currently under development with concurrent work being done on 2-slot TDMA and FDMA (CQPSK) modulation schemes. Phase II will use the Advanced Multi-Band Excitation AMBE vocoder to reduce the needed bitrate so that one channel will only require 4800 bits per second. Several vendors, including RELM support Phase II TDMA. Phase II has not been completely ratified yet.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 2 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.
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 including Australia, Singapore and Russia, although the Terrestrial Trunked Radio (TETRA) systems are more popular in Europe. And while Terrestrial Trunked Radio systems are sometimes cheaper - handsets are often not suited to more rugged environments. Both P25 and TETRA can offer varying degrees of functionality, depending on available radio spectrum, terrain and project budget.
While interoperability is a major goal of P25, many P25 features present interoperability challenges. In theory, all P25 compliant equipment is interoperable. In practice, interoperable communications isn't achievable without effective governance, standardized operating procedures, effective training and exercises, and inter-jurisdictional coordination. The difficulties inherent in developing P25 networks using features such as digital voice, encryption, or trunking sometimes result in feature-backlash and organizational retreat to minimal "feature-free" P25 implementations which fulfill the letter of any APCO-25 migration requirement without realizing the benefits thereof. Additionally, while not a technical issue per se, frictions often result from the unwieldy bureaucratic inter-agency processes that tend to develop to coordinate interoperability decisions.
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