[nos-bbs] Detail trace interpretation

[Jay Nugent]

Greetings Skip,

On Thu, 16 Feb 2006, George (Skip) VerDuin wrote:

> Greetings,
> 
> I'm looking at a detail trace for some AX.25 comm on VHF of last night
> from jnos.
> I'm OK with most of what I see, but stumble on a small detail I find no
> documentation for.
> 
> I find the following in the trace:
> 
> AX25: K8RRA->N8YJT RR(F) NR=0
> 
> I'm K8RRA, and at the moment this was created I was in contact with
> N8YJT.
> How should I interpret "RR(F)"?
> How does it differ from "RR(P)"?
> 
> This probably is not a jnos issue - it seems like an AX-25 standards
> issue... I really would like a detail description of (P) and (F) if one
> already exists. I rather expect I have missed one or more important
> document.

   The P and F are the Poll/Final bit in the Supervisory frame.  See the 
AX.25 Specification at:  http://www.tapr.org/pub_ax25.html



2.3.3 Functions of Poll/Final (P/F) Bit

 The P/F bit is used in all types of frames. It is used in a command 
(poll) mode to request an immediate reply to a frame. The reply to this 
poll is indicated by setting the response (final) bit in the appropriate 
frame. Only one outstanding poll condition per direction is allowed at a 
time. The procedure for P/F bit operation is described in 2.4.2. 



2.4.2 P/F Bit Procedures

The next response frame returned by the DXE to a SABM or DISC command with
the P bit set to 1 will be a UA or DM response with the F bit set to 1.

The next response frame returned to an I frame with the P bit set to 1, 
received during the information transfer state, will be a RR, RNR, or REJ 
response with the F bit set to 1. 

The next response frame returned to a supervisory command frame with the P 
bit set to 1, received during the information transfer state, will be a 
RR, RNR, or REJ response frame with the F bit set to 1. 

The next response frame returned to a S or I command frame with the P bit 
set to 1, received in the disconnected state, will be a DM response frame 
with the F bit set to 1. 

The P bit is used in conjunction with the time-out recovery condition 
discussed in 2.3.5.4, above. 

When not used, the P/F bit is set to zero. 




   Hope that helps.  

      --- Jay Nugent  WB8TKL
          o AEC Washtenaw - NTS Liasion & Packet Operations
          o Chair, ARRL Michigan Section "Digital Radio Group" (DRG)
            [www.MI-DRG.org]
          o Michigan AMPRnet IP Address Coordinator
            [www.mi-drg.org/ip-addr-form.html]

"Getting rid of terrorism is like getting rid of dandruff.  It cannot
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