[BXXPwg] Whither serial and seqno?

Sarveshwar Rao Duddu duddu@vsnl.com
Mon, 24 Jul 2000 00:08:51 +0530

Greg Hudson wrote:

> > At any point of time, multiple requests can be running on a single
> > or multiple channels.  So there should be some way for the sender to
> > associate the frame he is sending with a request. So we have the
> > serial number.
> This is simply incorrect.  Within a channel, responses must come in
> the same order as requests do.  So, as with, say, pipelined SMTP, no
> serial number is needed to associate requests with responses.

    Yes, responses must come in the sequence in which requests are sent.
    And requests must not be passed on to application as long as it has
    a pending request to respond. But that does not mean sender cannot
    send multiple requests. If the sender sends multiple requests without
    waiting for reply, then
    a. the first request is passed on the application.
    b. the application acts on it and responds to it.
    c. after the response is complete, beep passes on the
        next request to the application, if already in buffer.

    That is my understanding.

> > The receiver sends a SEQ frame with this new window size.  If we
> > dont have sequence number in the frame, then should the receiver
> > associate this with (1) or with (2) (see above)?
> Sure, it serves a purpose in the SEQ frame (perhaps SEQ should just
> have ackno+window instead of both, but there's no compelling argument
> either way).  But not in the REQ or RSP frames as far as I can tell.

    Sequence number is needed in SEQ frame. Not sure why it is in REQ/RSP.