Conventional Implementation
P25 systems do not support 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). This is a 12 bit code that prefixes every packet of data sent (including voice packets).
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 the digital signal being transmitted.
Since the NAC is a three-hexadecimal-digit number (12 bits), there are 4096 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.
Read more about this topic: Project 25
Famous quotes containing the word conventional:
“The mastery of one’s phonemes may be compared to the violinist’s mastery of fingering. The violin string lends itself to a continuous gradation of tones, but the musician learns the discrete intervals at which to stop the string in order to play the conventional notes. We sound our phonemes like poor violinists, approximating each time to a fancied norm, and we receive our neighbor’s renderings indulgently, mentally rectifying the more glaring inaccuracies.”
—W.V. Quine (b. 1908)