>Except in closed situations like 3GPP, how would the UA know whether to insert this new attribute? Those who think that the current behavior does not cause problems do not need to care about the attribute :) And, even in the current text: how does the UA know whether it needs to send the second "synchronization" offer? I guess one option is to provision it. Regards, Christer > > -----Original Message----- > > From: ietf-bounces@xxxxxxxx [mailto:ietf-bounces@xxxxxxxx] > On Behalf > > Of Ingemar Johansson S > > Sent: 07 October 2008 13:38 > > To: ietf@xxxxxxxx > > Cc: Flemming Andreasen; Ingemar Johansson S; > mmusic@xxxxxxxx; Christer > > Holmberg > > Subject: RE: [MMUSIC] Last Call: > > draft-ietf-mmusic-sdp-capability-negotiation(SDP Capability > > Negotiation) to Proposed Standard > > > > Hi > > > > In draft-ietf-mmusic-sdp-capability-negotiation it is proposed that > > the transport in the m-line is modified in the SDP answer. > While this > > is a good idea in order to reduce the number of > offer/answer exchanges > > it can in fact cause problems with intermediaries that for instance > > compare offer and answer SDP's. The problem may be > exacerbated further > > with the addition of extensions to the framework. > > > > Section 3.12 in the draft says: > > "The solution to this problem is to upgrade the intermediary to > > support the SDP Capability Negotiation framework". > > We find the conclusion unsatisfactory as the problem is that such > > upgrades are not done overnight and there will therefore, for a > > foreseeable future, exist middleboxes in the network that does not > > understand the SDP Capability Negotiation Framework. > > > > Our proposal to solve this issue is to introduce an > indicator in the > > SDP that tells that the actual configuration MUST only be > indicated on > > the a=acfg line. A proposed SDP attribute for this may be > > "a=spdcapneg-acfg-indication-only". > > > > In essence it means that (if the indicator is included in > the SDP) the > > first offer/answer exchange will only be done to get the actual > > configuration (a=acfg...). This would affect section 3.6.2 in the > > draft. > > If the indicator is included in the offer SDP it makes a 2nd > > offer/answer exchange a MUST in order to complete the offer/answer > > exchange. Section 3.6.3 specifies a "SHOULD" regarding the > behavior if > > the actual cofiguration and the SDP does not match. It is possible > > that "SHOULD" must be changed to "MUST" here. > > > > A UA that for some reason knows that intermediaries don't > understand > > the new framework it will add the said SDP attribute at the session > > level in the offer-SDP. > > Indications that intermediaries don't understand the new > framework may > > for instance in the 3GPP IMS case be that for a specific > 3GPP release > > the said attribute is mandated, a possible location for > such a text in > > this particular case is 3GPP TS26.114. > > > > We believe that the addition of the new functionality to > the framework > > will increase acceptance for the SDP Capability Negotiation > framework > > greatly and this without breaking the framework. > > > > PS. This issue has been raised previously in the MMUSIC WG, > still we > > want to bring this up again for your consideration. > > > > Regards > > > > Ingemar Johansson > > Christer Holmberg > > > > > > _______________________________________________ > > Ietf mailing list > > Ietf@xxxxxxxx > > https://www.ietf.org/mailman/listinfo/ietf > > > _______________________________________________ > mmusic mailing list > mmusic@xxxxxxxx > https://www.ietf.org/mailman/listinfo/mmusic > _______________________________________________ Ietf@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf