[MMUSIC] Proto identifier: To UDP or not to UDP (Re: Review of draft-ietf-mmusic-sctp-sdp-03)
Harald Alvestrand <harald@alvestrand.no> Thu, 21 March 2013 13:23 UTC
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Date: Thu, 21 Mar 2013 14:22:59 +0100
From: Harald Alvestrand <harald@alvestrand.no>
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To: Magnus Westerlund <magnus.westerlund@ericsson.com>
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Cc: draft-ietf-mmusic-sctp-sdp@tools.ietf.org, "mmusic (E-mail)" <mmusic@ietf.org>
Subject: [MMUSIC] Proto identifier: To UDP or not to UDP (Re: Review of draft-ietf-mmusic-sctp-sdp-03)
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One high level comment: This series of comments points out that the purpose of the thing called "proto identifier" in SDP is not really well documented. As far as I can tell, the requirement is that it uniquely identifies the parser one needs to use for the stuff under this m= line, and that is the sum total of the requirements on it - as we painfully learned with RTP/AVP, RTP/AVPF, SRTP/AVP and SRTP/AVPF, making detailed information about the parameters available via the "proto identifier" is not really a Good Idea. I suggest we go for DTLS/SCTP, as specified in the document currently, and document that the lower layer used has to be identified from the elements inside the m= line block; if there is ICE, ICE can negotiate it; if there is only a port number, it's UDP; if there are more extensions to specify that the lower layer is LTE over pterodactyls, the identifier doesn't change. Same handling as for RTP/AVP(F), and no double specifications. On 03/20/2013 04:11 PM, Magnus Westerlund wrote: > Hi, > > I have reviewed the SDP description of SCTP and have some comments and > suggestions. > > 1. My first comments is a very general one and concerns the relationship > between the proposed SCTP related proto identifiers and ICE for the > DTLS/SCTP encapsulation. > > When ICE was defined it was natural to include ICE by reftorfitting it > to existing proto identifiers. However, given that this specification > intorduce a number of new identifiers I do woner if we should be more > explicit about the ICE usage in the proto field. I think have both pro > and cons for this. > > So my considerations is basically to include specification of > ICE/DTLS/SCTP, where the lower layer transport is defined by what ICE > agrees on. This makes a lot of sense given that ICE can in fact arrive > on the usage of TCP/framing/DTLS/SCTP, TCP/TURN/DTLS/SCTP in addition to > more expected choices as UDP/DTLS/SCTP. This makes it clears that you do > require ICE to negotiate this transport flow. At the same time it is a > significant downside if ones negotiation needs are to chose between > using ICE or a specific lower layer transport. > > These comments doesn't apply when one runs SCTP on top of IP. > > 2. Section 1: > RFC4145 [RFC4145] specifies a general mechanism for > describing and establishing TCP (Transmission Control Protocol) > streams. > > I do dislike that usage of the RFC number as the explanation of what the > referenced document is. The previous sentence is how I prefer it to be > done: > SDP (Session Description Protocol) [RFC4566] provides a general- > purpose format for describing multimedia sessions in announcements or > invitations. > > Use the document title or an abbreviated explanation for what the > referenced document specifies and one gets much better flow in the > reading as one don't have stop look up the reference to find out what is > referred to. > > 3. Section 1: > I think having first a paragraph for SCTP and then having "Additionaly > .." with the other two protos are bit strange. Why not simpley say. This > document defines three proto identifiers: list of them with explnation. > > 4. Section 1: > DTLS/SCTP : to allow the usage of SCTP on top of the Datagram > Transport Layer Security (DTLS) protocol, as defined in > [I-D.tuexen-tsvwg-sctp-dtls-encaps], using SDP. SCTP over DTLS is > used by the RTCWeb protocol suite for transporting non- media data > between browsers. > > This definitions says nothing of the lower transport layer for DTLS/SCTP > even if UDP is referred to in a later section. I think this needs to be > clarified and discussed in the context of which lower layers do we > expect to be supported? From my perspective I think two makes sense. > ICE/DTLS/SCTP that allows ICE to negoiate what ever and then > UDP/DTSL/SCTP that only uses UDP as lower layer. Lets other add other > variants in the future if needed. > > 5. Section 3: > The 'DTLS/SCTP' protocol identifier indicates that the media > described will use SCTP on top of the Datagram Transport Layer > Security (DTLS) protocol as specified in > [I-D.tuexen-tsvwg-sctp-dtls-encaps]. > > I would like to point out that the referenced document does not at all > indicate what lower layer is being used under DTLS. > > 6. Section 4.1: > > This section discuss the usage of the "data channels" within the SCTP > association. My personal position is that for the moment this appears to > be unnecessary. The most important part is the SCTP association > establishment. Then one can discuss the general application using the > SCTP association as whole. Examples of such are WebRTC data channel. > > If anyone want stream level information in SDP then I propose that this > is handled as a extension to this signaling, not an from the start > included functionality as we don't appear to have clear requirement for > that. > > 7. Section 4.2: > > What are the requirements behind being able to establish multiple SCTP > association over the same DTLS connection? I am very unclear why this > would be required, and if not really needed I would suggest keeping > things simple. > > 8. Section 4.3: I guess this can for the moment be removed as it appears > to be taken care in other places, such as the RTCWEB WG data channel > protocol proposal. > > 9. If you are removing the multiple association and the "data channel" > parameters then most of the issues in section 5 vanish. If not I have > additional feedback on this section. > > 10. Section 8. > > Current NATs do not typically support SCTP. As an alternative to > design SCTP specific NATs, Encapsulating SCTP into UDP > [I-D.tuexen-sctp-udp-encaps] makes it possible to use SCTP in > networks with legacy NAT and firewalls not supporting SCTP. > > First of all, there is a WG version for this document: > draft-ietf-tsvwg-sctp-udp-encaps-14. Which is in IESG evaluation. Thus I > wonder why signalling for this is not included when all the other > options are included, even less mature ones then this? > > To me it looks like this document need to have some high level decisions > on what to include and not and then try to finish it up within the > agreed constraints. From my perspective I think it should focus on a > single SCTP association per m= line and the actual SCTP association. > > Cheers > > Magnus Westerlund > > ---------------------------------------------------------------------- > Multimedia Technologies, Ericsson Research EAB/TVM > ---------------------------------------------------------------------- > Ericsson AB | Phone +46 10 7148287 > Färögatan 6 | Mobile +46 73 0949079 > SE-164 80 Stockholm, Sweden| mailto: magnus.westerlund@ericsson.com > ---------------------------------------------------------------------- > > _______________________________________________ > mmusic mailing list > mmusic@ietf.org > https://www.ietf.org/mailman/listinfo/mmusic
- [MMUSIC] Review of draft-ietf-mmusic-sctp-sdp-03 Magnus Westerlund
- Re: [MMUSIC] Review of draft-ietf-mmusic-sctp-sdp… Paul Kyzivat
- Re: [MMUSIC] Review of draft-ietf-mmusic-sctp-sdp… Magnus Westerlund
- [MMUSIC] Proto identifier: To UDP or not to UDP (… Harald Alvestrand
- Re: [MMUSIC] Review of draft-ietf-mmusic-sctp-sdp… Paul Kyzivat
- Re: [MMUSIC] Review of draft-ietf-mmusic-sctp-sdp… Magnus Westerlund
- Re: [MMUSIC] Proto identifier: To UDP or not to U… Magnus Westerlund
- Re: [MMUSIC] Review of draft-ietf-mmusic-sctp-sdp… Mary Barnes
- Re: [MMUSIC] Review of draft-ietf-mmusic-sctp-sdp… Paul Kyzivat