Hello,
I recently picked up on decoding EDACS Extended Addressing (EA) again, since now I can actually hear the voice traffic on the local system. In going over some notes and logs I discovered a few more details I missed.
Since EA changed the meaning of some of the messages, I wondered how to detect an EA system and what technique is used to prevent a non-EA radio from trying to use a EA system. The radio compares the site id with the value programmed in the radio. If there is a match, it uses the site.
On non-EA systems the site id is contained in a message that has the data bits
where d is the slot delay, c is the control channel, p is the priority level, h is home flag, f is failsoft, and i is the site id. The site id is 6 bits so there are 64 possible site ids.
On EA systems the same message is used but the control channel is sent in another message. The site ids are in the range of 33 to 63 but the specifications say hundreds of sites are possible. So there are id bits somewhere else.
I had a doh moment today when I looked at the site id messages from several EA systems. I suspect that non-EA systems had a site limit below 32 sites even with six bits assigned. Setting the msb of the site id would prevent a non-EA radio from getting a match during the site id comparison. If I eliminate that bit, and use the former control channel bits, I get a match for reported site ids. So a EA system has a site id message of
where e is set one to indicate extended addressing. I assume the d, p, h, and f bits have the same meaning on either system. This means that an EA system can have up to 1,023 sites.
The side effect with the original trunker-based programs is when system ids of 32 to 63 (20 to 3f in hex) come up then it is an EA system and can not be tracked.
73 Eric
I recently picked up on decoding EDACS Extended Addressing (EA) again, since now I can actually hear the voice traffic on the local system. In going over some notes and logs I discovered a few more details I missed.
Since EA changed the meaning of some of the messages, I wondered how to detect an EA system and what technique is used to prevent a non-EA radio from trying to use a EA system. The radio compares the site id with the value programmed in the radio. If there is a match, it uses the site.
On non-EA systems the site id is contained in a message that has the data bits
Code:
dd ccccc ppp h ff iiiiiiOn EA systems the same message is used but the control channel is sent in another message. The site ids are in the range of 33 to 63 but the specifications say hundreds of sites are possible. So there are id bits somewhere else.
I had a doh moment today when I looked at the site id messages from several EA systems. I suspect that non-EA systems had a site limit below 32 sites even with six bits assigned. Setting the msb of the site id would prevent a non-EA radio from getting a match during the site id comparison. If I eliminate that bit, and use the former control channel bits, I get a match for reported site ids. So a EA system has a site id message of
Code:
dd iiiii ppp h ff eiiiiiThe side effect with the original trunker-based programs is when system ids of 32 to 63 (20 to 3f in hex) come up then it is an EA system and can not be tracked.
73 Eric
