NXDN Console

angelotinti

Newbie
Joined
Feb 3, 2021
Messages
2
I'm trying to develop a console to interact with ICOM equipament through NXDN protocol. I connected in a repeater through IP network and were able to capture packages sent by the repeater with Wireshark, and now i'm actually trying to decipher those packages and understand what is what. Been using the NXDN docs, specially the first file where we can find info about Common Air Interface and i'm sure i'm missing something. The document mention Layers 1, 2 and 3, and a lot of types of channels and frames that can be sent and received with message types and etcetera. I've been able to send and receive status and text messages but can't really understand the structure of the UDP packages. I mean, i know that some bytes here and there are indicating source id, destination id, and this helped me a little, but theres a lot of data that i'm not being able to comprehend. Already looked some open source projects on github but they dont implement all the functionalities. Actually all the projects that i've been able to find just implement Voice and they have a lot of hardcoded stuff, like the header for voice packages:

const unsigned char HEADER[] = { 0x83U, 0x01U, 0x10U, 0x00U, 0x0FU, 0x01U, 0x00U, 0x20U };

I did find this sequence on one of the packets received, but what this data really means? I know for a fact that the sixth byte representes the message type defined as layer 3 in the document. But for other packets, the message type can be a different byte, probably due to pre-bytes that should represent other infos, but what do they represent? Well, i'm lost.

A frame is either L1, L2, L3 or all the layers are present?

I havent been able to find FSW, LICH or Preamble anywhere, and as far as i understand from the manual, those should always be present.
If anyone could help me pointing a direction, i would appreciate very much. I could even pay for a consulting if necessary.
 

slicerwizard

Member
Joined
Sep 19, 2002
Messages
6,962
Location
Toronto, Ontario
I don't see why IP network traffic would need preambles, frame sync patterns, etc. I doubt that the standards specify how vendors implement the back end of a system.
 

angelotinti

Newbie
Joined
Feb 3, 2021
Messages
2
The vendor manual points to the NXDN CAI document, and reading the CAI and coulnt really understanding how to decipher a package from a software behind IP/TCP protocol perspective. I dont have expertise with radio communications, thats probably why I was looking for preamble, frame sync, etc. Well, that's a start, so I will not find those kind of informations on the packates received from the repeater.
 
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