Draft Minutes, SIP Working Group, IETF 56

edited by Dean Willis

The SIP Working Group met at IETF 56 on Monday, March 17, 1300-1500, in room Continental 6.

The posted agenda:

1300 Agenda Bash
1305 Status -- Chairs
1315 Non-Invite Transaction Issues, Robert Sparks
    draft-sparks-sip-noninvite-00.txt
1330 Referred-By Changes and Open Issues, Robert Sparks
   draft-ietf-sip-referredby-01.txt
1340 Resource Priority, Henning Schulzrinne
     draft-polk-sip-resource-02.txt
1355 Caller Preferences, Jonathan Rosenberg
     draft-ietf-sip-callerprefs-08.txt
1410 Congestion Safety, Dean Willis, Hisham Khartabil
     draft-ietf-sip-congestsafe-01.txt
      draft-khartabil-sip-congestionsafe-ci-02.txt
1430 Authenticated ID Bodies, Jon Peterson
     draft-ietf-sip-authid-body-01.txt
1445 SIPit report on S/MIME and TLS, Rohan Mahy
1455 General Discussion
1500 Break

Scribe: Ramu (notes not receivedby chairs)
Chart Room Coordinator: Not recorded

Topic: Non-invite transactions, Robert Sparks.

The slides presented are included in the proceedings.

Poll == who as read and understands the draft, app. 20%. Discusssion: Principle problem is the race condition of 64*T1 built into the protocol. Given non-zero latency, the UAS side has an offset on this time, so the client may time out before the server completes. Now we just try and "complete as soon as possible" giving response codes like 408 that make no sense -- by the time it gets back to the UAC, the UAC is assured of having timed out, creating a 408 storm. Other problems exist with intermediary timeouts and with forking convergence.

Two solutions offered: A and B. Rohan argues against proposal B, preferring the subscribe/notify style of seperate transactions. Point: What if values of T1 are different? Discussion: If UAS and UAC have different values of T1, it's all broken anyhow. Extended discussion follows. Two problems: the infrequent 1 in 10,000 events, and the problem that the 200 has to be emitted soon enough to have a high probability to make it back to the UAC before the 408s. Most troubling is when the UAS thinks the situation is 200ok, but the UAC has a different view (which can happen with non-invite forking). Point that we should lift the constraint on interoperability with existing proxies. Suggestion we adhoc during this meeting for consensus -- group to email Robert for gathering. Note: a detailed adhoc on this topic was held later and the minutes seperately included in the proceeedings.

Topic: Referred-by, Robert Sparks

The slides presented are included in the proceedings.

Complaint: nobody is giving feedback. Are people mostly happy and just waiting on some of the blocking work to complete? A chairs asks for volunteers to provide feedback: Brian Rosen, Mary Barnes, Alan Johnston, Pekka Pessi all volunteer.

Issue: Use of Call-ID seems to be required in auth-ID-body. Is it a leak? Should we put garbage in, change the AID body format, or what? Jon Peterson reports that the newest AIB draft relieves this requirement.

Issue: Referred identity binding between REFER and INVITE. Can a referee assert a different identity on the generated INVITE than was referenced in the REFER? Can humans make the distinction? No resolution of this issue in this meeting, but it seems to relate to the URI Leasing work ongoing in SIPPING.

Topic: Resource-Priority, Henning Schulzrinne

The slides presented included in the proceedings.

Goal: Higher priority of emergency call completion during service disruption of civil emergency, especially in interworking with PSTN. Requirements are establised in RFC3487. List discussion reviewd, best option a new header. Discussion about whether it is "good" to have proxies understand this. Consensus: Work on this problem, starting from this draft as a baseline, but address additional opinions and requirements as raised in the WG process.

Topic: Caller Preferences, Jonathan Rosenberg

The slides presented are included in the proceedings.

Issue: Needs a thorough review of the current draft, which seems pretty much "done".

Volunteers to review -- Robert Sparks, Mary Barnes, Pekka Pessi, Bob Penfield, Cullen Jennings. The plan is to review, feed back, revise, go to 2 week WGLC.

Topic: Congestion Safety, Dean Willis and Hisham Khartabil

Presentation by Dean Willis. Slides presented included in the proceedings.

General poll indicates that after reading the draft, nobody understands how it works. People seem to have the vague feeling that the topic is important but are not cognizant of the implications. Suggestion made that "congestion safe" is a misnomer, as nothing is "safe". No consensus reported.

Presentation by Hisham Khartabil. Slides presented included in proceedings.

One point made from audience is that implementors do not see immediate value. Proposed by one speaker that we should consider response-CI as a possible alternate mechanism in primary work. No consensus reported.

Topic: Auth-ID Issues, Jon Peterson

Slides presented are included in the proceedings.

The only new "SIP" function is the new 400-response code. Other functions are non-normative. No poll for consensus recorded.

Meeting concluded at 1500.