Subject: RTSP: Question on sequence numbers

From: Pete Cordell <[email-masked]>
Date: Mon, 28 Apr 1997 18:27:48 +0100

Although not brought out as an issue in the RTSP draft, there is quite a
bit of discussion (section 8.2) on whether the sequence number of the
command should or should not be incremented when a RTSP message is sent
as a result as a re-transmission (when using rtspu).

In the text is says that it should be incremented so that accurate RTT
calculations can be made, but as the text says this does not cope with
receiving commands in the wrong order.  There seems to be a conflict
here with the previous paragraph that says things can be pipelined.  

Also, if the response to a play is lost on the return path, the server
won't know whether a play message is sent because of transmission loss,
or because that is what the client wanted it to do.  i.e. the server
might get:

play range:10-15
play range:10-15

This might be because the client wants the same bit twice, or the
response to the first message got lost.

As getting the sequence of user commands right seems more important than
getting the rtt calculation right this sounds like an issue to me.  Am I
missing something here, or should this be on the issues list?

Pete

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Pete Cordell
BT Labs
E-Mail: [email-masked]
Tel: +44 1473 646436
Fax: +44 1473 643791
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Notice:  This contribution is the personal view of the author and 
does not necessarily reflect the technical nor commercial direction 
of British telecommunications plc.
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