Re: [rtcweb] Working Group Last Call for draft-uberti-rtcweb-rfc8829bis-01.txt

[Christer Holmberg <[e-mail]>]

Hi,

If the text is something that everyone can agree on, then I suggest we go with that. It does not require any changes or assumptions regarding the endpoint behaviour.

Regards,

Christer

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________________________________
From: Justin Uberti <[e-mail]>
Sent: Friday, November 5, 2021 7:12:02 AM
To: Christer Holmberg <[e-mail]>
Cc: Cullen Jennings <[e-mail]>; RTCWeb IETF <[e-mail]>; Roman Shpount <[e-mail]>
Subject: Re: [rtcweb] Working Group Last Call for draft-uberti-rtcweb-rfc8829bis-01.txt

I still feel the cleanest solution would be to allow the answerer to accept a subsequent offer as an initial offer (since then things will work in 3PCC with no SDP rewriting), and AFAIK no technical reason has been put forth to explain why this cannot work.

However, I can live with the alternate solution put forth by Christer, and the proposed text seems reasonable to me.

Justin

On Thu, Nov 4, 2021 at 9:14 PM Christer Holmberg <[e-mail]<mailto:[e-mail]>> wrote:

Hi,



The question was whether an endpoint would be assumed to be able to accept a subsequent offer (same address:port in each m- line) as an initial offer. I did not agree to that.



However, the suggestion a couple of days ago, which people seemed to agree to, does NOT make that assumption anymore. Nothing out of the normal would be assumed by endpoints, and instead the 3GPP controller will act as a B2BUA and modify the SDP if needed.



Regards,



Christer



From: Cullen Jennings <[e-mail]<mailto:[e-mail]>>
Sent: perjantai 5. marraskuuta 2021 5.34
To: Christer Holmberg <[e-mail]<mailto:[e-mail]>>; Roman Shpount <[e-mail]<mailto:[e-mail]>>; Justin Uberti <[e-mail]<mailto:[e-mail]>>
Cc: RTCWeb IETF <[e-mail]<mailto:[e-mail]>>
Subject: Re: [rtcweb] Working Group Last Call for draft-uberti-rtcweb-rfc8829bis-01.txt





Could we have a quick call on this next week during one of the breaks. I have tried to follow this whole thread and some it does not make much sense to me. I’m a bit lost on what the varios proposed resolutions are.





On Nov 3, 2021, at 12:38 PM, Christer Holmberg <christer.holmberg=[e-mail]<mailto:christer.holmberg=[e-mail]>> wrote:



Justin, are you ok with the suggested text? I would probably be a good idea to refer it in 8829bis.



Regards,



Christer

________________________________

From: rtcweb <[e-mail]<mailto:[e-mail]>> on behalf of Christer Holmberg <christer.holmberg=[e-mail]<mailto:christer.holmberg=[e-mail]>>
Sent: Tuesday, November 2, 2021 11:13 PM
To: Roman Shpount <[e-mail]<mailto:[e-mail]>>
Cc: Justin Uberti <[e-mail]<mailto:[e-mail]>>; RTCWeb IETF <[e-mail]<mailto:[e-mail]>>
Subject: Re: [rtcweb] Working Group Last Call for draft-uberti-rtcweb-rfc8829bis-01.txt



Hi,



>This makes it much better. I think it is missing a couple of commas ("In some 3PCC scenarios," and "In the rewritten offer,") but works for me.



I can add them when I add the text to the draft, but I think the RFC editor will most likely notice such thing.



>I have changed the section name so it is clear that it applies to JSEP as well, not just SIP.



Sure, that’s fine.



Regards,



Christer







On Tue, Nov 2, 2021 at 1:24 PM Christer Holmberg <[e-mail]<mailto:[e-mail]>> wrote:

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 <[e-mail]<mailto:[e-mail]>>
Sent: Tuesday, November 2, 2021 6:33 PM
To: Christer Holmberg <[e-mail]<mailto:[e-mail]>>
Cc: Justin Uberti <[e-mail]<mailto:[e-mail]>>; Justin Uberti <[e-mail]<mailto:[e-mail]>>; RTCWeb IETF <[e-mail]<mailto:[e-mail]>>
Subject: Re: [rtcweb] Working Group Last Call for draft-uberti-rtcweb-rfc8829bis-01.txt



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





On Tue, Nov 2, 2021 at 6:00 AM Christer Holmberg <[e-mail]<mailto:[e-mail]>> 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 <[e-mail]<mailto:[e-mail]>>
Sent: tiistai 2. marraskuuta 2021 10.41
To: Justin Uberti <[e-mail]<mailto:[e-mail]>>
Cc: Christer Holmberg <[e-mail]<mailto:[e-mail]>>; Justin Uberti <[e-mail]<mailto:[e-mail]>>; RTCWeb IETF <[e-mail]<mailto:[e-mail]>>
Subject: Re: [rtcweb] Working Group Last Call for draft-uberti-rtcweb-rfc8829bis-01.txt



On Mon, Nov 1, 2021 at 2:52 PM Justin Uberti <[e-mail]<mailto:[e-mail]>> wrote:

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 (https://www.ietf.org/archive/id/draft-ietf-mmusic-rfc8843bis-05.html#name-sip-consideration), 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



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