Re: [rtcweb] partial review of draft-ietf-rtcweb-sdp-01
Suhas Nandakumar <suhasietf@gmail.com> Tue, 31 May 2016 20:25 UTC
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Date: Tue, 31 May 2016 13:25:35 -0700
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From: Suhas Nandakumar <suhasietf@gmail.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: Re: [rtcweb] partial review of draft-ietf-rtcweb-sdp-01
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Thanks Paul for reviewing the draft. We will go through your comments and get back to you. In the meanwhile, I suggest people to HTML rendering of the draft for ease of readability. Here is the link: https://tools.ietf.org/id/draft-ietf-rtcweb-sdp-01.html Thanks Suhas On Tue, May 31, 2016 at 12:09 PM, Paul Kyzivat <pkyzivat@alum.mit.edu> wrote: > Another general issue: > > I have been *trying* to verify the consistency in use of ports, IP > addresses, fingerprints, ice ufrag info, ice passwords, ssrcs, cnames, etc. > > Of course this is excruciating to do. (For a reviewer like me, and also > for a potential implementer trying to understand the examples.) > > My preliminary take is that there are a number of errors. A lot of them > are probably cut/paste errors. With sufficient analysis it is sometimes > possible to figure out what was intended vs. what is written. But it is > hard with this much stuff. > > It would be easier if, instead of using random sample values, the values > were replaced with semantically relevant and easily recognized values. > (E.g., "ALICE-SSRC-1", "TED-CNAME-2") Unfortunately I don't think this can > be done while also having those values by syntactically valid. > > I think I will end up making such a replacement myself, in a local copy, > simply to assist in analyzing what is there. > > Thanks, > Paul > > > On 5/30/16 6:14 PM, Paul Kyzivat wrote: > >> Ted asked if I would do a review of draft-ietf-rtcweb-sdp-01. I started, >> but it is taking a long time. I'm sending what I have so far to give you >> something to consider/work on. >> >> In order to simplify this review for both me and readers, I will in >> general only mention an issue once, the first time I find it, and be >> silent on future occurrences of the same issue. >> >> * In general in the examples it would be very helpful if you would >> include a blank line prior to each m-line. When reading these it is >> currently hard to find the m-lines, which is something needed when >> trying understand and compare things. >> >> * Section 3: >> >> I realize this is for a webrtc oriented reader, so I am trying to >> understand it from that perspective. Even so, I have trouble with >> classifying a=ice* as "Security Descriptions". Given the existing >> categories I would think they better belong in "Stream Description". >> >> * Section 5.1: >> >> o The term "Session" is used rather loosely in this document to >> refer to either a "Communication Session" or a "RTP Session" or a >> "RTP Stream" depending on the context. >> >> This seems like a bad idea. It may be forgivable to mix communication >> session and RTP session in examples where a single bundle is used for >> all media, or there is only one m-line. But not if multiple m-lines >> aren't bundled, and not with RTP Stream. >> >> OTOH, so far I haven't noticed any place where this is an issue. >> >> * Section 5.2.1: >> >> The SDP line-wrapping convention described in 5.1 isn't being used in >> the example. >> >> Is there a reason for including the IP address in the a=rtcp line, when >> it is the same as the address in the c= line, which is the default? >> >> Is there any expectation that a=ptime:60 only applies to opus? IIUC this >> should be interpreted ad applying to all codecs mentioned in the m-line. >> (There is no order-dependence among attributes within a single media >> section. AFAIK there is no way of specifying a separate ptime for >> individual codecs in an m-line.) >> >> Use of sha-1 in a=fingerprint is about to become incorrect according to >> draft-ietf-mmusic-4572-update-03. That work is being driven by rtcweb, >> so I would think you would want to reflect it here. >> >> The way tables are formatted in RFC format can make the examples >> confusing to readers: the label for table 1 falls exactly between the >> bottom of the table it describes and the following table. When viewed on >> a screen it is difficult to tell what each table is. I suggest tweaking >> the contents of the tables to make this clearer. E.g., >> >> +----------------------------------+--------------------------------+ >> | SDP Contents - Offer | RFC#/Notes | >> +----------------------------------+--------------------------------+ >> >> In Table 2, the o-line has two spaces after the "-". It should only be >> one. >> >> * Section 5.2.3: >> >> Table 5 has ice and fingerprint attributes prior to the first m-line. >> >> The m-line and associated attributes for the data channel is >> inconsistent with draft-ietf-mmusic-sctp-sdp-16. I think it ought to be >> (more or less): >> >> m=application 56966 UDP/DTLS/SCTP webrtc-datachannel >> c=IN IP4 24.23.204.141 >> a=mid:data >> a=sctp-port:5000 >> a=setup:actpass >> ... >> >> If you really want to negotiate the usage of channel 1, then it also >> needs to include: >> >> a=dcmap:1 subprotocol="chat";label="channel 1" >> >> (Note: this presumes that "chat" is a registered subprotocol. It isn't!) >> >> * Section 5.2.4: >> >> This seems fine if Bob intends to send audio (e.g. MoH). If not then it >> would be better to answer a=inactive. >> >> * Section 5.2.5: >> >> Has there been any discussion of pros/cons of having DTMF on a separate >> m-line and a separate ssrc? If one or both ends actually think of DTMF >> as being part of another audio stream then this might present problems. >> This could especially be true for interoperation with telephony devices. >> >> Is there anything in rtcweb that prevents having these on the same >> m-line and ssrc? >> >> * Section 5.2.7: >> >> Note that the BAS concept has been removed from Bundle, so you at least >> shouldn't refer to it. (You can still do the O/A if you want.) >> >> In Table 14 (answer), why are ice attributes and fingerprints given >> separately (and differently) for the two m-lines? (Even though the ports >> and addresses are the same.) This is contrary to current bundle (-29) >> procedures. >> >> In the 2nd (BAS) offer there is a gratuitous change in ordering of >> several of the attributes. (Makes it difficult to see what has changed.) >> I also don't understand the other differences between the ice and >> fingerprints in audio and video, and between this and the first offer. >> >> * Section 5.2.8: >> >> This example *assumes* bundle support, and so uses the same addr/port >> for bundled m-lines. But this will fail badly if the assumption turns >> out to be wrong. When making this assumption you ought to use >> bundle-only in the initial offer to ensure nothing bad happens if the >> assumption of bundle support by answerer turns out to be wrong. AFAIK >> there is no downside to doing this. >> >> Again this doesn't follow current bundle rules. >> >> ======= >> >> That's as far as I have gotten. (Slow going.) I'll try to get you more >> later. >> >> Thanks, >> Paul >> >> _______________________________________________ >> rtcweb mailing list >> rtcweb@ietf.org >> https://www.ietf.org/mailman/listinfo/rtcweb >> >> > _______________________________________________ > rtcweb mailing list > rtcweb@ietf.org > https://www.ietf.org/mailman/listinfo/rtcweb >
- [rtcweb] partial review of draft-ietf-rtcweb-sdp-… Paul Kyzivat
- Re: [rtcweb] partial review of draft-ietf-rtcweb-… Paul Kyzivat
- Re: [rtcweb] partial review of draft-ietf-rtcweb-… Suhas Nandakumar