Hi, I assume that the INVITE contained an SDP and your example truly reflects a single dialog (i.e. 18x/2xx To tags are the same).
According to RFC 3261 section 13.2.1, the SDP modification must be ignored. Thus it shouldn't cause the call to be released. With that said, some devices have configuration options to violate that statement and treat as an updated answer SDP (or a new offer SDP). RFC 3261 section 13.2.1: "The UAC MUST treat the first session description it receives as the answer, and MUST ignore any session descriptions in subsequent responses to the initial INVITE." More inline. > -----Original Message----- > From: sip-implementors-boun...@lists.cs.columbia.edu [mailto:sip- > implementors-boun...@lists.cs.columbia.edu] On Behalf Of Roger Wiklund > Sent: Thursday, September 17, 2015 1:47 PM > To: sip-implementors@lists.cs.columbia.edu > Subject: [Sip-implementors] SDP version increment without SDP change in early > dialog > > Hi list > > I'm seeing the following behavior from an Aastra 400 PBX. > > Flow below is ITSP to PBX > > INVITE> > <100Trying > <183 w/SDP > PRACK> > <200OK (PRACK) > <180 w/SDP > >PRACK > <200OK (PRACK) > <200OK (INVITE)w/SDP > ACK> > BYE> > <200OK (BYE) > > Each time the PBX sends an SDP, the version number is incremented even though > nothing is changed. > > ITSP does not like this and sends the BYE. > > I'm trying to wrap my head around this and to figure out who's at fault here. > > According to RFC6337 section 3.2 > > When both UAs support the 100rel extension, they can update the session in > the early dialog once the first offer/answer exchange has been completed. > > To me that means that the UAS can send many provisional responses each with > different SDP, each one updates the early dialog as long as PRACK is used. RFC6337 section 2.2 (and RFC 3261) only allows 1 offer/answer for a dialog's INVITE/response/ACK. After the INVITE's offer/answer completes; PRACK and UPDATE can be used for new offer/answer exchanges before the INVITE transaction completes. _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
