Capwap Mailing List: Re: Recap of current pending issues

[Pat Calhoun (pacalhou) (pcalhoun]

> Issue 159 (Question on CAPWAP control protocol). This was a question, 
> which I have responded to. There was no need for change, unless Pasi 
> raises a specific issue. At this point, I consider this issue closed.

The answer (you can't have multiple outstanding requests) really needs
to be in the spec. Also, the spec needs some more text about how the
receiver processes them -- e.g. does the receiver maintain "last seen
sequence number" counter, and silently drop (without
replying) requests older than this? 


I believe some of this was already covered, but I have added a new
sentence to the end of the first paragraph. I am including some
additional language that does address some of your concern that was
already in the spec:

<text>
4.5.3.  Retransmissions

   The CAPWAP control protocol operates as a reliable transport.  For
   each Request message, a Response message is defined, which is used to
   acknowledge receipt of the Request message.  In addition, the control
   header Sequence Number field is used to pair the Request and Response
   messages (see Section 4.5.1).  This Request/Response pair, combined
   with the Sequence Number, implies that both the WTP and the AC can
   only have a single request outstanding at any given time.

   Response messages are not explicitly acknowledged, therefore if a
   Response message is not received, the original Request message is
   retransmitted.  Implementations MAY cache Response messages to
   respond to a retransmitted Request messages with minimal local
   processing.  Retransmitted Request messages MUST NOT be altered by
   the sender.  The sender MUST assume that the original Request message
   was processed, but that the Response message was lost.  Any
   alterations to the original Request message MUST have a new Sequence
   Number, and be treated as a new Request message by the receiver.

</text>

PatC