respond to system requests between transmissions. Phase 2 is what is known as 6.25 kHz "bandwidth equivalent" which satisfies an FCC requirement for voice transmissions to occupy less bandwidth. Voice traffic on a Phase 2 system transmits with the full 12.5 kHz per frequency allocation, as a Phase 1 system does, however it does so at a faster data rate of 12 kbit/s allowing two simultaneous voice transmissions. As such subscriber radios also transmit with the full 12.5 kHz, but in an on/off repeating fashion resulting in half the transmission and thus an equivalent of 6.25 kHz per each radio. This is accomplished using the AMBE voice coder that uses half the rate of the Phase 1 IMBE voice coders. Beyond Phase 2 From 2000 to 2009, the European Telecommunications Standards Institute (ETSI) and TIA were working collaboratively on the Public Safety Partnership Project or Project MESA (Mobility for Emergency and Safety Applications), which sought to define a unified set of requirements for a next-generation aeronautical and terrestrial digital wideband/broadband radio standard that could be used to transmit and receive voice, video, and high-speed data in wide-area, multiple-agency networks deployed by public safety agencies. The final functional and technical requirements have been released by ETSI and were expected to shape the next phases of American Project 25 and European DMR, dPMR, and TETRA, but no interest from the industry followed, since the requirements could not be met by available commercial off-the-shelf technology, and the project was closed in 2010. During the United States 2008 wireless spectrum auction, the FCC allocated 20 MHz of the 700 MHz UHF radio band spectrum freed in the digital TV transition to public safety networks. The FCC expects providers to employ LTE for high-speed data and video applications. Conventional implementation P25 systems do not have to resort to using in band signaling such as Continuous Tone-Coded Squelch System (CTCSS) tone or Digital-Coded Squelch (DCS) codes for access control. Instead they use what is called a Network Access Code (NAC) which is included outside of the digital voice frame. This is a 12-bit code that prefixes every packet of data sent, including those carrying voice transmissions. The NAC is a feature similar to CTCSS or DCS for analog radios. That is, radios can be programmed to only pass audio when receiving the correct NAC. NACs are programmed as a three-hexadecimal-digit code that is transmitted along with