====== Reading AX.25 Traces ======

Often in packet radio you will see output like this:

{{:packet:sample-trace.png?400|}}


AX.25 2.2 packets are either "commands" or responses".  Commands can have a "P" poll bit set, and responses will echo that back as an "F" final bit.

  * C is often used for SABM (Set Asynchronous Balanced Mode) - Creates a new AX.25 2.0 connection. 
  * SABME (Set Asynchronous Balanced Mode Extended - Creates a new AX.25 2.2 connection. 
  * RR (Receive Ready) - I'm ready to receive more data. 
  * RNR (Receive Not Ready) - don't send me more data right now. 
  * REJ (REJect) - I'm missing some data, please retransmit everything from this point. 
  * SREJ (Selective REJect)  - I'm missing some data, please retransmit just this packet. 
  * DISC (DISConnect) - Please disconnect.
  * FRMR (FRaMe Reject) - You previous frame was invalid and I didn't like it.
  * I (Information) - the actual data. 
  * UI (Unnumbered Information) - Information sent outside of a connection.
  * DM (Disconnect Mode) - You asked me to disconnect, and I did.
  * XID (eXchange IDentification) - This is what features I supported.
  * TEST (Test) - "ping?"
  * UA (Unnumbered Acknowledgement) - I successfully received and accepted your previous packet. 

Example flow:
   - <color #ed1c24>M7QQA>M7QQB <SABM C P></color> - M7QQA would like to open a connection to M7QQB.
   - <color #00a2e8>M7QQB>M7QQA <UA R F></color> - M7QQB confirms connection to M7QQA.
   - <color #00a2e8>M7QQB>M7QQA <I C P R0 S0> "Welcome to M7QQB."</color> - M7QQB sends a connection banner to M7QQA.
   - <color #ed1c24>M7QQA>M7QQB <RR R F R1></color> - M7QQA has received all messages before sequence 1, and is ready to receive more.

   - The first field is the frame type.
   - The second field is "C" for control message, or "R" for response message.  
   - The third field is "P"/"F" for poll/final, or omitted if not set.
   - S# means "This packet has sequence number #."
   - R# means "I have received all packets before sequence number #."

====Additional reading====
{{ :packet:bpqterminal_frames.pdf |}}

{{ :packet:decifering_packet_frame_headers.pdf |}}

{{tag>frame frames traces}}