[MMUSIC] Final MMUSIC Minutes from 57th IETF
Joerg Ott <jo@tzi.uni-bremen.de> Fri, 15 August 2003 08:00 UTC
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Date: Fri, 15 Aug 2003 09:59:37 +0200
From: Joerg Ott <jo@tzi.uni-bremen.de>
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Subject: [MMUSIC] Final MMUSIC Minutes from 57th IETF
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Folks, since we have not received any comments, we consider the minutes final. The slides are available at http://www.dmn.tzi.org/ietf/mmusic/57/slides/57-mmusic-slides-ppt.zip http://www.dmn.tzi.org/ietf/mmusic/57/slides/57-mmusic-slides-pdf.zip Joerg ------------------------------------------------------------------------ Minutes of the MMUSIC WG Meeting at the 57th IETF ================================================= Reported by Joerg Ott and Colin Perkins Notes taken by Colin Perkins The MMUSIC WG met once at the 57th IETF. The meeting was chaired by Colin Perkins and Joerg Ott. It was attended by some 90 participants. Status Update ------------- Joerg Ott reported on the status of the working and the general progress since the 56th IETF in San Francisco: - The new charter was finally approved. - RFC 3524 was published on SDP extensions for reservation flows. - Two documents are with the RFC editor: SDP extensions for NAT traversal and SDPng transition. - Two documents are with the IESG, and comments have been received: - draft-rajeshkumar-mmusic-gpmd-03.txt was felt to overlap with work on capability negotiation carried out elsewhere; it was noted that this probably applies to most of SDP except that SDP was first. The chairs and authors will work with the IESG to sort this out. - draft-ietf-mmusic-sdp-new-13.txt received many comments which were discussed in a separate slot (see below). - Two documents are under AD review: - draft-ietf-mmusic-sdp-srcfilter-05.txt - draft-ietf-mmusic-sdp-comedia-05.txt - draft-ietf-mmusic-sdp-bwparam-04.txt is completing WGLC on 28 Jul 2003. - The SDP extensions for key management (draft-ietf-mmusic-kmgmt-ext-07.txt) have been waiting for the MIKEY work to complete which seems to progress. A further revision is expected shortly after the IETF. - The SDP implementation draft draft-ietf-mmusic-sdp-implem-00.txt has not been revised yet, but Tom Taylor is working on it. He is trying to incorporate further implementation experience from inside his company as well as from the SIPit events. Two potential new work items have been discussed for MMUSIC: - Real-time fax (draft-ietf-sipping-realtimefax-01.txt) from the SIPPING WG is to provide implementers with guidelines on how to use registered SDP attributes for ITU-T T.38. This document actually contains two logical parts: the use of offer/answer mechanics (which belongs to MMUSIC) and a discussion of SIP-specific signaling (which belongs to SIPPING). It is suggested to investigate splitting the document to deal with each one in the respective WG. But it was pointed out that this document merely contains examples only and hence should be done as a whole in just one WG. To be resolved. - Interactive connectivity establishment (ICE) also from the SIPPING WG (draft-rosenberg-sipping-ice-01.txt). This is discussed later on the agenda. Revised SDP (draft-ietf-mmusic-sdp-new-13.txt) ---------------------------------------------- Colin Perkins reported on the changes incorporated in the latest revision of SDP: It was attempted to clarify when the k= attribute may be used. Further clarifications include: RTP may be used with non-consecutive port numbers and a=charset is only allowed as a session level attribute. Also, unregistered X- attributes and media format are deprecated. Finally, IANA considerations and references were updated. Colin further reported on issues raised on revision -13 on the mailing list, as well as from the IESG review. - An ABNF inconsistency was found: a comment in the ABNF for "token-char" allowed for a larger set of characters than the actual definition. One could either (1) change the comment to match the actual grammar (and thus reduce the set of allowed characters) or (2) modify the grammar to match the comment. The group agreed to go with option (1), pending a check against the use of SDP in RFC 3108. Tom Taylor volunteered to find this out. - The use of b= with layered coding should be clarified as follows: When using the CT modifier with RTP, if several RTP sessions are part of the conference, the conference total refers to total bandwidth of all RTP sessions. This was accepted in principle but it was also pointed out that a bandwidth specification per layer would be helpful. Further discussion is needed on the mailing list. - Again with layered coding, it should be clarified which ports are associated with an m= line. The clarification proposal was accepted. - The k= is underspecified. The most straightforward way would be to deprecate the use of this field altogether. Opinions from implementers are sought. It was reported that MS Messenger uses this field; the details are unknown at this moment though. As there are implementation out there, just deprecating this field won't work. Therefore, further work needs to go into the specification of using k=. In particular, when k= shall be used, a secure channel must be available and endpoints need to be sure that no third party can eavesdrop on the key. These issues, however, need to be specified by those using SDP rather than SDP itself. The k= field currently supports an algorithm indicator, but it should also specify a key type. This may be implied by the URI or the media protocol used. For more complex scenarios, e.g. when more than one key is needed, either the sdescriptions work (draft-ietf-mmusic-sdescriptions-01.txt) or the key management (draft-ietf-mmusic-kmgmt-ext-07.txt) work should be used. It was proposed that the security considerations section should change "SHOULD NOT deliver the user into an interactive multimedia session..." to "MUST NOT...". It was found that this is an issue of user authorization (e.g. the user may be able to pre-authorize the automatic joining of certain interactive sessions) and needs to be dealt with by the protocols using SDP. - The suggestion to define a "IN" value for private address spaces was rejected because systems 1) cannot tell whether they are in a private address space (relative to their peers) and 2) this change would be not backward compatible. - It will be clarified that UTF-8 normalization is not needed because comparisons are not done on fields with UTF-8. - Proposal on a=inactive: it was agreed not to change the SDP spec here (this is an issue for users of SDP, which may establish conventions for use, not for SDP itself). - Wording should be added that u= and k= may include URIs that may be dereferenced in some (but not all) cases. Also, it should be noted a k= URI may typically be an http or https URI. Both suggested wording additions were accepted. Colin will fold the comments and the discussion into the document and produce a new revision out within a couple of weeks. SDP Security Descriptions (draft-ietf-mmusic-sdescriptions-01.txt) ------------------------------------------------------------------ Dan Wing briefly reviewed the document and the changes from the previous revision: a new syntax is proposed for the a=crypto attribute and the offer/answer part is revised which may need further review. For the next steps, Colin noted that an IANA considerations section is needed, including a discussion of the registration procedures. Furthermore, reviewers for finishing the document were sought: Tom Taylor, Magnus Westerlund, and Martin Euchner volunteered. Offer/Answer Examples (draft-johnston-mmusic-offer-answer-examples-01.txt) -------------------------------------------------------------------------- Alan Johnston presented the changes to the document: in particular, an example for asymmetric use of a codec has been added. This is to be achieved using two distinct m= lines with the same port number, one indicating "sendonly", the other "recvonly". The proposed behavior caused some discussion: it was felt that the mechanism was underspecified and that (therefore) m= lines with the same port would be a bad idea. Yet, the right approach to achieve the desired behavior seemed unclear. Gonzalo Camarillo pointed out that the RFC3388 provided a similar example, but with an explicit grouping (which is not present in this draft). The applicability of RFC3388 to this problem was discussed further. Orit Levin pointed out that the intention clearly is to use RFC 3388 but the question is what happens to the endpoints that don't support RFC 3388. Gonzalo argued that this is already defined in RFC 3388. The chairs stated that they would like to see the asymmetric codec behavior with two m= line properly specified in a document. The present offer/answer examples draft is meant to be illustrative; the example should be kept in place (with added grouping) but the normative text for this behavior needs to be someplace else. Flemming Andreasen suggested to specify part of this practice in the revised SDP. SDPng Update (draft-ietf-mmusic-sdpng-06.txt) --------------------------------------------- Dirk Kutscher presented the latest progress on SDPng, addressing the open issues from draft -06 (a new revision still needs to be submitted). The SDPng structure has been enhanced to decouple capability negotiation for potential configurations from actual configuration (and the respective session parameters). While the capability model has been kept, the syntax has been revised to exclusively rely on XML mechanisms (rather than embedding own syntax conventions for attributes) -- which is less efficient but much cleaner. Dirk presented the new syntax using several examples and also showed a formal schema definition. A further refinement from draft -06 is to remove the concept of libraries and use inline definitions instead -- so that SDPng documents would be self-contained. There was little discussion. Steve Casner asked whether this work was getting enough traction and questioned whether people were really preparing for a transition. Joerg Ott argued that people are desparately holding onto SDP (which is perceived easier with one small extension at a time) -- but that examples show that this getting more complicated so that SDP is likely to have only a finite lifetime. So it would be nice to get broader review from the community on a replacements for SDP. RTP DoS Attacks (draft-rosenberg-mmusic-rtp-denialofservice-00.txt) Interactive Connectivity Establishment (draft-rosenberg-sipping-ice-01.txt) --------------------------------------------------------------------------- Jonathan Rosenberg introduced the RTP DoS problem: An attacker may easily direct the RTP stream(s) from an unsuspecting source to any target by providing the target's IP address in the SDP. This works for SIP and RTSP -- with RTSP providing limited protection by allowing unicast RTP streams only to the address of the originator (but NATs make it worse as anyone behind the same NAT can easily be attacked). As authentication mechanisms can at most help identify the attacker (which may be very weak though), some kind of handshake mechanism is needed so that sources do not start sending media streams unless they know that the right receiver is actually waiting for it: a request/response mechanism using the RTP ports is needed. This is ICE (see below) which has been chosen as a solution for SIP. However, ICE has broader applicability and may be appropriate for RTSP, too -- which needs to be determined by the group. Jonathan reviewed the properties of the ICE approach and briefly walked through the basic ICE algorithm. With ICE being signaling protocol independent, MMUSIC is asked to take ICE up as a WG item. ICE is felt to introduce quite some complexity for RTSP endpoints. If, however, NAT traversal (which is an RTSP issue on its own, see below) and security can be addressed by the same mechanism, it may be worth the effort. It is noted that even if we go for the ICE mechanism for RTSP right now, this does not solve the problem as long as old RTSP servers are still out there. Regarding the ICE proposal as a WG item Magnus Westerlund argued that if it is accepted, one should split the draft into several parts: the SIP use, the ICE mechanism, the use with offer/answer, etc. There was consensus in the group to accept ICE as new WG item, and to fully document the RTP DoS issues as an informational document. RTSP Update (draft-ietf-mmusic-rc2326bis-04.txt ----------------------------------------------- Magnus Westerlund reported on the progress of the RTSP revision, achieved by having a new co-editor joining the team, many teleconference calls, and also quite some list discussion. He presented a number of changes from draft -03 (see the slides). With this, most known open issues are resolved, with only a few ones remaining (see slides). But many resolutions still need to be folded into an updated revision of the draft. When this is done, a second phase of editing on the spec is needed: examples need to be fixed, the spec's consistency needs to be checked as needs it overall readability, and, potential new open issues need to be solved. With all this, the revised RTSP spec will not meet the October deadline as currently documented in the MMUSIC charter. Magnus suggests another six months would be appropriate to finalize the work. RTSP and NAT (draft-ietf-mmusic-rtsp-nat-01.txt) ------------------------------------------------ Magnus Westerlund introduced the revised draft on RTSP and NATs, the purpose of which is to describe how to traverse NATs and firewalls with RTSP. It documents several possible NAT traversal approaches and gives recommendations regarding RTSP for firewalls. Approaches requiring only modifications on the client side STUN, TURN, and RTP/RTSP tunneled in RTSP. Application-Layer Gateways (ALGs) for RTSP will not require any modifications -- but are generally discouraged. Magnus further discussed open issues, particurlarly the goals for RTSP for NATs (i.e. what type of scenarios should be achievable) as well as possible solutions (symmetric RTP, STUN, ICE, DCCP). On the ALGs: The group generally agreed that ALGs are a bad thing and should not be considered further (except for documentation purposes and to communicate this clearly to outside the IETF -- and fast, as people start deploying these). On the document's purpose: Commenters state that, currently, the draft does not give conclusive resolution of what to do as an implementer, it is merely an inventory. It is proposed to pick some solution and write it up, e.g. in the RTSP spec. Magnus wants to resolve the structure of the document and then settle on a solution: one for the server and one or more for the client side. Jonathan Rosenberg and Tom Marshal argue over the number of client-side solutions to be documented: Jonathan wants only one while Tom prefers to have multiple feasible solutions document. In case multiple ones are documented, Jonathan wants exactly one "MUST implement" solution to ensure interoperability. There was some further discussion on technical aspects of possible solutions, but no real conclusions were reached. Internet Media Guides (IMG) --------------------------- draft-nomura-mmusic-img-requirements-01.txt draft-nomura-mmusic-img-framework-01.txt After a brief introduction by Joerg Ott, Rod Walsh presented the progress on the IMG requirements document (which will be re-submitted as WG draft by end of August). He briefly reviewed the general topology and IMG distribution aspects and then went through the requirement categories identified in the draft: IMG description requirements and IMG transport requirements. The former primarily address IMG envelopes for existing meta-data formats, the latter their distribution in unicast and multicast, pull and push style scenarios. For multicast push, SAPv2 is probably inadequate, so a successor is sought, e.g. ALC from the RMT WG. It is pointed that additions to ALC need to be specified separately; while Rod wants to use the RMT proposal FLUTE, Lorenzo argues that this may not be 100% appropriate here; Lorenzo also points out that possible tasks in the RMT WG need to happen quickly as the group is trying to wrap up. For unicasting, client-initiated actions could use HTTP while notifications from the server could use SIP mechanims. Rod discusses on the scalability requirements IMG transport and presents a conceptual overview showing the different pieces of an IMG framework and outlines the achieved flexibility. He also addresses data relationships and particularly security considerations as taken into account in the requirements draft. Rod finally discusses the way ahead: the requirements draft is pretty close to finalization; the remaining efforts are mainly editorial and consolidation. The aim is to go for WGLC soon. He also points to the existing framework draft that will be revised by the end of August. _______________________________________________ mmusic mailing list mmusic@ietf.org https://www1.ietf.org/mailman/listinfo/mmusic