p25

Project 25 (P25 or APCO-25) is a suite of standards for digital mobile radio communications designed for use by public safety organizations in North America. P25 radios are a direct replacement for analog UHF ( example FM) radios but add the ability to transfer data as well as voice, allowing for a more natural implementation of encryption or messaging. P25 radios are commonly implemented by dispatch organizations, such as police, fire, Ambulance and Emergency Rescue Service, using vehicle-mounted radios combined with walkie-talkie handheld use.
Starting around 2012, products became available with the newer phase 2 modulation protocol, the older protocol known as P25 became P25 phase 1. P25 phase 2 products utilise the more advanced AMBE2+ vocoder, which allows audio to pass through a more compressed bitstream and provides two TDMA voice channels in the same RF bandwidth (12.5 kHz) that phase 1 can only provide one voice channel. The two protocols are not compatible. However, P25 Phase 2 infrastructure can provide a "dynamic transcoder" feature that translates between Phase 1 and Phase 2 as needed. In addition to this, phase 2 radios are backwards compatible with phase 1 modulation and analog FM modulation, per the standard. On the other hand, EU area created the standard for Terrestrial Trunked Radio similar to Project 25.
P25 fills a similar role as TETRA or DMR protocols.

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