the digital signal being transmitted. Since the NAC is a three-hexadecimal-digit number (12 bits), there are 4,096 possible NACs for programming, far more than all analog methods combined. Three of the possible NACs have special functions: 0x293 ($293) – the default NAC 0xf7e ($F7E) – a receiver set for this NAC will pass audio on any decoded signal received 0xf7f ($F7F) – a repeater receiver set for this NAC will allow all incoming decoded signals and the repeater transmitter will retransmit the received NAC. 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 Project 25. It is also being used in other countries worldwide including Australia, New Zealand, Brazil, Canada, India and Russia. As of mid-2004 there were 660 networks with P25 deployed in 54 countries. At the same time, in 2005, the European Terrestrial Trunked Radio (TETRA) was deployed in sixty countries, and it is the preferred choice in Europe, China, and other countries. This was largely based on TETRA systems being many times cheaper than P25 systems ($900 vs $6,000 for a radio) at the time. However P25 radio prices are rapidly approaching parity with TETRA radio prices through increased competition in the P25 market. The majority of P25 networks are based in Northern America where it has the advantage that a P25 system has the same coverage and frequency bandwidth as the earlier analog systems that were in use so that channels can be easily upgraded one by one. Some P25 networks also allow intelligent migration from the analog radios to digital radios operating within the same network. 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 Project 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