Re: [MMUSIC] I-D Action:draft-ietf-mmusic-rfc2326bis-19.txt

[Magnus Westerlund <magnus.westerlund at ericsson.com>]

Joe Pallas skrev:
> 
> On Dec 1, 2008, at 4:45 AM, Magnus Westerlund wrote:
> 
>>> | 16.19.  CSeq
>>>
>>> I wonder why we have it at all. I assume I must be missing something.
>>> It made
>>> sense for rtspu, but now? It is quite trivial to implement for
>>> clients and
>>> servers, but not for proxies.
>>
>> As section 10 says:
>>
>>    Certain RTSP headers, such as the CSeq header (Section 16.19), which
>>    may appear to be relevant only to connectionless transport scenarios
>>    are still retained and must be implemented according to the
>>    specification.  In the case of CSeq, it is quite useful for matching
>>    responses to requests if the requests are pipelined (see Section 12).
>>    It is also useful in proxies for keeping track of the different
>>    requests when aggregating several client requests on a single TCP
>>    connection.
> 
> But is it doing anything useful?  HTTP proxies function perfectly well
> without any equivalent.  The rules for RTSP pipelining are the same as
> non-pipelined requests: that responses must be delivered in the same
> order as requests, so there is nothing that the CSeq field adds.
> 
> I think there is a strong case to be made that CSeq only ever made sense
> for unreliable transports, and there is no value that it adds for
> reliable transports.  While it does not do much harm, it really seems to
> be unnecessary.

I agree that the header is not necessary for the functioning of the
protocol. I think the main argument for keeping it is debugging and
handling error cases, like lost message boundaries requiring
resynchronization of the message flow. Please do remember that TCP is
not guaranteed free from errors.

Cheers

Magnus Westerlund

IETF Transport Area Director & TSVWG Chair
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