Hello,
I am mainly focusing on decoding Type-C and Type-D trunking since control channels are available 24/7. I was able to add enough decoding to decode the id, site number, and Type-D repeater number. I tuned around and linked together the multiple Type-C and Type-D channels I heard into systems. AAA in NH uses a Type-D system in Goffstown, NH, so it tends to be active after business hours.
The RAN is the site number mod 64 on Type-C systems, and a zero value does not match everything. Like other systems, the system id and site number are sent often, so the RAN value is not required for monitoring Type-C systems. Type-D does not use RAN.
Having the NXDN specification really helps, but one still has to wade through it. The common problem is the size and organization. You need to look in 4 or more different places for information on a frame. IDAS Type-D trunking is covered in two separate documents that copy like Conventional/Type-C documents with modifications. The contents of some messages are different on Type-D, but it does not appear to be too difficult to select the proper message format to use.
Type-D trunk systems are a digital form of enhanced analog LTR, so there is the concept of Free Repeaters, and Home Repeaters.
It appears Type-C uses a frequency mapping concept similar to P25 and other non-LTR systems. I have not found much about the mapping. The system ID uses a system category concept similar to DMR Tier-3. The category indicates where to split the id number into the system id and site id numbers. So the local category has a small number of sites and a large number of system ids while the global category has a large number of sites and a small number of system ids.
Both Type-C and Type-D have provisions for inter-system linking.
73 Eric