[OpenSIPS-Users] SDP version increment without a change in SDP

[Adrian Fretwell]

Hello All,  I have an issue for which I have not been able to find a 
definitive answer in the RFCs.

I use RTPProxy as part of NAT traversal so RTP streams are set up 
between upstream provider and my proxy, and between my proxy and the UAC.

The problem I have, is UAC changes it's RTP port between 183 and 200 OK 
and thus increments the SDP version number, BUT the ports DO NOT change 
between proxy and upstream provider but the SDP version number does, 
because it is passed through.  The upstream provider says this violates 
RFC 4566 and sends an immediate BYE after the final ACK.

I read that RFC 4566 says:

" /<sess-version> is a version number for this session description.  Its//
//      usage is up to the creating tool, so long as <sess-version> is//
//      increased when a modification is made to the session data.  Again,//
//      it is RECOMMENDED that an NTP format timestamp is used/."

The problem is I can't find an RFC stating "You MUST NOT increment
version number if no change is made to the SDP".

So I must either:

1. Prove that it should be OK to increment the version number without 
any change to the SDP.  Or

2. Find a way of not passing through the incremented version number to 
the upstream side where the SDP has not actually changed.

I hope that makes sense...  As always any help very nuch appreciated.

Kind regards,

Adrian Fretwell
Nottinghamshire
UK
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