Original text:
possible, and media sections will not be marked as bundle-only.  This is by design, but could cause issues in the rare case of sending a subsequent offer as an initial offer to a non-bundle-aware endpoint <del> via Third Party Call Control (3PCC). </del>  "a=group:LS" attributes are generated in the same way as for initial offers, with the additional stipulation that any lip sync groups that

Reviewer comments:
and
To resolve WGLC comments: URL it was agreed to incorporate a reference to this text in 8843bis: URL That text ended up in s7.6.
When draft-8843bis is given an RFC number, this draft should reference the new RFC. Hi, Eventhough I would not like to make more changes than necessary, I am fine with "3PCC Considerations". However, your suggested text is very difficult to understand in some places, so let me give it a try. (The first paragraph is generic, the second SIP specific, and the third BUNDLE specific.) 3PCC Considerations In some 3PCC scenarios a new session will be established between an endpoint that is currently part of an ongoing session and an endpoint that is currently not part of an ongoing session. The endpoint that is part of a session will generate a subsequent offer that will be forwarded to the other endpoint by a 3PCC controller. The endpoint that is not part of a session will process the offer as an initial offer. The Session Initiation Protocol (SIP) [RFC3261] allows a User Agent Client (UAC) to send a re-INVITE request without an SDP body (sometimes referred to as an empty re-INVITE). In such cases, the User Agent Server (UAS) will include an SDP offer in the associated 200 OK response. If the UAS is a part of an ongoing session, it will include a subsequent offer in the 200 OK response. The offer will be received by a 3PCC controller (UAC) and then forwarded to another User Agent (UA). If the UA is not part of an ongoing session, it will process the offer as an initial offer. When the BUNDLE mechanism is used, an initial BUNDLE offer is constructed using different rules than subsequent BUNDLE offers, and it cannot be assumed that a UA is able to correctly process a subsequent offer as an initial offer. Therefore, the 3PCC controller SHOULD rewrite the subsequent offer into a valid initial offer, following the procedures in (Section 7.2), before it forwards the offer to a UA. In the rewritten offer the 3PCC controller will set the port value to zero (and include an SDP 'bundle-only' attribute) for each "m=" section within the BUNDLE group, excluding the offerer-tagged "m=" section. __ From: Roman Shpount Sent: Tuesday, November 2, 2021 6:33 PM To: Christer Holmberg Cc: Justin Uberti ; Justin Uberti ; RTCWeb IETF Subject: Re: [rtcweb] Working Group Last Call for draft-uberti-rtcweb-rfc8829bis-URL How about we replace the SIP Considerations with: 3PCC Considerations In some 3PCC scenarios, an offer generated during an ongoing session, i.e., a subsequent offer, will be used by a 3PCC controller to establish a new session and forwarded as an initial offer to another endpoint that is currently not part of a session. For example, the Session Initiation Protocol (SIP) [RFC3261] allows a User Agent Client (UAC) to send a re-INVITE request without an SDP body (sometimes referred to as an empty re-INVITE). In such cases, the User Agent Server (UAS) will include an SDP offer in the associated 200 OK response. If UAS is a part of an ongoing session, it will include a subsequent offer in the 200 OK response. The offer will be received by a 3PCC controller (UAC) and then forwarded to another User Agent (UA) as an initial offer. When the BUNDLE mechanism is used, an initial BUNDLE offer is constructed using different rules than subsequent BUNDLE offers. It cannot be assumed that a subsequent offer is a valid initial offer and that the endpoint that expects an initial offer will properly process such a subsequent offer. Therefore, the 3PCC controller SHOULD rewrite the subsequent offer into a valid initial offer before it is used to establish a new session. To make the subsequent offer a valid initial offer, 3PCC will need to modify all the non-tagged m= lines to include the bundle-only attribute and set the m= line port to zero. _ Roman Shpount Christer Holmberg > wrote: Hi, What about something like this: OLD: “The Session Initiation Protocol (SIP) [RFC3261] allows a User Agent Client (UAC) to send a re-INVITE request without an SDP body (sometimes referred to as an empty re-INVITE). In such cases, the User Agent Server (UAS) will include an SDP Offer in the associated 200 OK response. This is typically used for 3rd Party Call Control (3PCC) scenarios. >From a BUNDLE perspective, such SDP Offer SHOULD be generated using the procedures defined in Section 7.2.” NEW: “The Session Initiation Protocol (SIP) [RFC3261] allows a User Agent Client (UAC) to send a re-INVITE request without an SDP body (sometimes referred to as an empty re-INVITE). In such cases, the User Agent Server (UAS) will include an SDP offer in the associated 200 OK response. This is typically used for 3rd Party Call Control (3PCC) scenarios. In some 3PCC scenarios the UAS will be part of an ongoing session, and will therefore include a subsequent offer in the 200 OK responses. The offer will be received by a 3PCC controller (UAC) and then forwarded as an initial offer to another User Agent (UA) that is currently not part of a session. When the BUNDLE mechanism is used, as an initial BUNDLE offer look different than a subsequent BUNDLE offer, it cannot be assumed that a UA that expects an initial offer will be able to properly process a subsequent offer. Therefore, the 3PCC controller needs to act as a Back-To-Back User Agent (B2BUA), and when it receives the subsequent offer it needs to rewrite it into an initial offer before it is forwarded to such UA.” Regards, Christer From: Roman Shpount > Sent: tiistai 2. marraskuuta 2021 10.41 To: Justin Uberti > Cc: Christer Holmberg >; Justin Uberti >; RTCWeb IETF > Subject: Re: [rtcweb] Working Group Last Call for draft-uberti-rtcweb-rfc8829bis-URL The PROBLEM is that we have two endpoints, where one sends a subsequent offer, and the other one expects an initial offer. What do you normally do when you have that kind of problem? You use an SBC/B2BUA. In this case that SBC/B2BUA would be the 3PCC controller. So, my suggestion would be to remove the SHOULD text from 8843bis, and simply add a note somewhere (in 8843bis and/or 8829bis) which describes the issue and says that the 3GPP controller needs to modify the offer accordingly. Roman, thoughts on this? If the 3PCC is going to rewrite the offer SDP anyway then maybe adding a=bundle-only isn't the end of the world. I am not opposed to this idea. 3PCC typically knows that the subsequent offer is going to be used as initial, and should be able to rewrite the offer to make it valid. We can change SIP Considerations section in 8843bis (URL), remove the SHOULD, and specify that 3PCC controller should fix the offer. We can then reference this note from 8829bis or restate the same guidance. Roman Shpount
Not seeing any objections for a month then once -02 is submitted we will progress this towards our AD. spt

Revised text:
possible, and media sections will not be marked as bundle-only.  This is by design, but could cause issues in the rare case of sending a subsequent offer as an initial offer to a non-bundle-aware endpoint  <ins> via Third Party Call Control (3PCC), as discussed in I-D.ietf-mmusic- rfc8843-bis. </ins> "a=group:LS" attributes are generated in the same way as for initial offers, with the additional stipulation that any lip sync groups that