Project 25

Project 25 (P25 or APCO-25) is a suite of standards for digital radio communications for use by federal, state/province and local Public safety organizations 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 Terrestrial Trunked Radio (TETRA) protocol, but the two are not interoperable. The major difference between the two is P-25 is expected to work jointly with existing analog systems. Therefore, it uses "simulcast" method for control. "Simulcast" refers to the use of the same set of control channels throughout a given area, which are "simultaneously broadcast, or simulcast" in the region. In contrast, TETRA uses "Multicast", which means the control channel is embedded, therefore there is no need to use a separate channel to broadcast control signals. TETRA provides 4 slots per channel, which means four voice calls can be handled on one channel. This is similar to the GSM cellular system, which contains eight slots with seven usable, allowing seven users per channel.

Public safety radios have been upgraded from analog to digital since the 1990s because of the limitations of analog transmission, and the technological advances brought with digital radio.

Various user protocols and different public safety radio spectrum made it difficult for Public Safety agencies to achieve interoperability and widespread acceptance. However, lessons learned during disasters the United States faced in the past decades have forced agencies to assess their requirements during a disaster when basic infrastructure has failed. To meet the growing demands of public safety digital radio communication, the United States Federal Communications Commission (FCC) at the direction of the United States Congress initiated a 1988 inquiry for recommendations from users and manufacturers to improve existing communication systems. Based on the recommendations, to find solutions that best serve the needs of public safety management, in October 1989 APCO Project 25 came into existence in a coalition with:

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