Hi,

While testing a SIP client I work on I noticed that there was some
interoperability issue with a certain PBX. This PBX will issue a
re-INVITE to both call legs once the call is established so that they
direct the RTP directly, without traversing the server. While doing
this, the origin SDP attribute is also modified in the following way:

Initial INVITE:

o=root 1697225829 1697225829 IN IP4 192.168.1.79

re-INVITE

o=root 1697225829 1697225830 IN IP4 192.168.1.47

RFC3264, sec 8 says the following:

"When issuing an offer that modifies the session,
   the "o=" line of the new SDP MUST be identical to that in the
   previous SDP, except that the version in the origin field MUST
   increment by one from the previous SDP."

By reading that I understand that this PBX is doing it wrong because
the host is also changed. However, I tested this same thing with a
Snom phone and it did accept the re-INVITE.

So, is there any RFC updating this section? If not, is it OK to apply
Postel's principle here?


Thanks for any input!

-- 
/Saúl
http://saghul.net | http://sipdoc.net

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