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:
“We must be generously willing to leave for a time the narrow boundaries in which our individual lives are passed ... In this fresh, breezy atmosphere ... we will be surprised to find that many of our familiar old conventional truths look very queer indeed in some of the sudden side lights thrown upon them.”
—Bertha Honore Potter Palmer (18491918)