Re: [MMUSIC] 4566bis outstanding issues - Send, receive asymmetry and port numbers
Paul Kyzivat <pkyzivat@alum.mit.edu> Wed, 06 August 2014 13:47 UTC
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Date: Wed, 06 Aug 2014 09:47:36 -0400
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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References: <C15918F2FCDA0243A7C919DA7C4BE9940ECF6C11@xmb-aln-x01.cisco.com> <539263E2.8010802@alum.mit.edu> <281DBAD0-3E23-4F2C-ABD0-6F8D5CB47629@cisco.com> <E851980F-648E-41E1-A200-64BF720D91F5@cisco.com> <53BAA873.6050907@alum.mit.edu> <EE893C03-926F-427C-B4ED-61EF7601130B@cisco.com> <53BAD9A0.6060304@alum.mit.edu> <6A5A8D4EF65AF1439301480747E29F434E42B417@STOEXMBX01.sr.se> <5BF924B8-20CB-4CB2-A152-B49ED07651CD@cisco.com> <9D8A6737-45D2-44A5-84D1-772754B6E861@sverigesradio.se>
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Subject: Re: [MMUSIC] 4566bis outstanding issues - Send, receive asymmetry and port numbers
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Fredrik, There is now a solution to your asymmetric use case, using the BUNDLE draft: draft-ietf-mmusic-sdp-bundle-negotiation-07. Thanks, Paul On 8/6/14 5:49 AM, Fredrik Bergholtz wrote: > The change, however, does not address the “same port” issue. Section > 5.14 of rfc 4566 states: “The semantics of multiple "m=" lines using the > same transport address are undefined.” The text is not perfectly clear > on what the “transport address” is, but it is implied that this is, in > fact the “port” number(s). My thinking is that this restriction is only > valid when the directionality of the media descriptions are the same. > > The following is an example of an asymmetrical SDP that might be used in > a radio broadcast use-case. From a reporter in the field, a reasonably > high audio quality is required but the return from the studio to the > reporter only need to be good enough for spoken cues. > > |v=0| > |o=mtu-02 3599993974 3599993974 IN IP4 example.com <http://example.com>| > |s=mtu-02| > |c=IN IP4 203.0.113.12| > |t=0 0| > |m=audio 5004 RTP/AVP 96| > |a=rtpmap:96 aptx/32000/1| > |a=fmtp:96 variant=enhanced; bitresolution=24| > a=sendonly > |a=ptime:20| > m=audio 5004 RTP/AVP 9 > |a=rtpmap:9 G722/8000| > |a=recvonly| > > As I understand it, this SDP example would strictly have undefined > semantics even though I think that the semantics are very clear. > > I don’t have any concise candidate text that clarifies my points but I > could try to think of some if there are no technical issues with the > approach that I am unaware of. > > Best regards, > Fredrik Bergholtz > Swedish Radio > > P.S. I am not a native English speaker, so all my suggested text would > have to be validated. > > > > On 05 Aug 2014, at 16:32, Ali C. Begen (abegen) <abegen@cisco.com > <mailto:abegen@cisco.com>> wrote: > >> Hi Fredrik >> >> There were some changes in the bis document regarding these attributes >> in -08: >> http://www.ietf.org/rfcdiff?url1=draft-ietf-mmusic-rfc4566bis-07&url2=draft-ietf-mmusic-rfc4566bis-08 >> >> Do they help with your issue? If not, what else would you like to see? >> >> >> I remember seeing a discussion regarding the use of the same port at >> some point but it was another draft (sorry I dont remember which one >> it was). >> >> -acbegen >> >> On Aug 5, 2014, at 3:35 PM, Fredrik Bergholtz >> <fredrik.bergholtz@sverigesradio.se> wrote: >> >>> Hi. Excellent to see a summarised list of what is considered for 4566bis. >>> >>> Personally I would like to see ABNF definitions for all the >>> attributes. I do realise the amount of work that is needed but, as >>> someone else mentioned, the 4566 is the base line for all extensions >>> and I think that it is important to make the base as well-defined as >>> possible. >>> >>> One item that is not in your list that I would like to see is a >>> clarification of how to signal asymmetric sessions. By asymmetric >>> sessions I mean using the a=sendonly and a=recvonly in separate media >>> definitions, specifically addressing the "same port" issue of section >>> 5.14. >>> >>> I realise that this is a more use-case oriented addition than an >>> improvement of the examples for the various attributes that has been >>> discussed. Perhaps this kind of clarification belong in something >>> like rfc4317 rather than in 4566. Do you have any thoughts on if and >>> how such clarifications could and should be made? >>> >>> Best regards, >>> Fredrik Bergholtz >>> Swedish Radio >>> >>>> -----Original Message----- >>>> From: mmusic [mailto:mmusic-bounces@ietf.org] On Behalf Of Paul Kyzivat >>>> Sent: den 7 juli 2014 19:32 >>>> To: mmusic@ietf.org >>>> Subject: Re: [MMUSIC] 4566bis outstanding issues >>>> >>>> Trimming again. >>>> >>>> On 7/7/14 12:16 PM, Ali C. Begen (abegen) wrote: >>>>> >>>>> On Jul 7, 2014, at 11:02 PM, Paul Kyzivat <pkyzivat@alum.mit.edu> >>>>> wrote: >>>>> >>>>>> On 7/7/14 4:07 AM, Ali C. Begen (abegen) wrote: >>>>>>> Hi Paul, >>>>>>> >>>>>>> OK, no one else seems to be paying attention to this. I have some >>>> comments inline and lets see whether we can reach an agreement: >>>>>> >>>>>> OK. >>>>>> >>>>>> I've trimmed to a few points to comment on... >>>>>> >>>>>>>>> On 6/6/14 5:19 PM, Ali C. Begen (abegen) wrote: >>>>>> >>>>>>>>>> 1) 4566bis needs to provide ABNF syntax for all of the >>>>>>>>>> attributes 4566 >>>> defined. >>>>>>>>>> Comments: This was discussed again in a side meeting in London and >>>> there was not a consensus whether we actually needed this. >>>>>>>>> >>>>>>>>> IIRC the argument against doing this is that we might get it wrong. >>>>>>>>> >>>>>>>>> But IMO we should do it because if we can't get it right how can we >>>> expect readers to get it right? >>>>>>> >>>>>>> I personally don't wanna take on this task. It is a tedious task >>>>>>> and I am not >>>> such an ABNF lover to get these definitions right. If you wanna >>>> volunteer, by all >>>> means, please do so. >>>>>> >>>>>> I'm willing to contribute to this, but won't have time until after >>>>>> the Toronto >>>> meeting. >>>>> >>>>> That is fine. >>>>> >>>>>> Also, I'm not intimately familiar with all of the attributes. >>>>> >>>>> Nobody is I am afraid. >>>> >>>> There are a lots of people who at least *use* them, and so are >>>> familiar with >>>> them at that level. I don't "do" media, so when I'm trying to create >>>> examples I >>>> can get as far as "m=audio", and I know there should be an >>>> "a=rtpmap", but >>>> beyond that I need to find an example to copy. >>>> >>>>>>> OK, this goes back to the issue #1. Personally, I suggest we do >>>>>>> not define the >>>> abnfs for every sdp attribute in 4566, but then you have a good >>>> point. We can >>>> seek a format and provide a few good examples to show prospective >>>> authors. >>>>>>> >>>>>>> To do this, obviously as you said, we need to agree on that >>>>>>> format. Has >>>> there been a proposal in the past or does anyone have a good >>>> proposal to start >>>> with? >>>>>> >>>>>> Not a formal one. There has been some discussion about this during >>>>>> review >>>> of individual attribute definitions. My take has been that there is >>>> not agreement. >>>>> >>>>> If you can recall, can you point us to that proposal and maybe >>>>> briefly explain >>>> the disagreements as well? >>>> >>>> I think it will take a lot of searching to find it. So I can't do so >>>> quickly/easily. >>>> >>>>>> One question is whether the definition of a new attribute should: >>>>>> 1) define the full syntax of the line (starting with "a="), >>>>>> 2) should provide additional definitions of <attribute> (via "/=") >>>>>> 3) should provide additional definitions of <att-field> and >>>>>> <att-value> >>>>>> (via "/=") >>>>>> 4) provide definitions of the name and value that are consistent with >>>>>> <att-field> and <att-value> without formally extending the >>>>>> definitions of those. >>>>>> >>>>>> Note that 4566 loosely follows (4) but gives the definitions >>>>>> informally rather >>>> than via ABNF. So it gives no guidance on how to use ABNF for this. >>>> A number of >>>> drafts have chosen to follow (2). Some have started to do (1) but I >>>> don't know of >>>> any that ended up that way. >>>>>> >>>>>> A question I have raised is: if (2) or (3) is followed, does that >>>>>> mean that the >>>> draft doing so must be considered as "updating" 4566? >>>>> >>>>> I dont see why it should. Personally most of the attributes I >>>>> defined followed >>>> (4). That seemed the easiest option. >>>> >>>> I've been outnumbered on the discussions of this. ISTM that whenever >>>> I write >>>> >>>> attribute =/ something new >>>> >>>> then I have at least extended the rfc that defines <attribute> and >>>> arguably have >>>> updated it. The reason it might be considered an update is that what >>>> I am >>>> defining implicitly includes the definition of <attribute> and thus >>>> probably all the >>>> abnf that includes the definition of <attribute>. To verify my new >>>> abnf, or to >>>> generate a parser, I need to create a combined abnf. And abnf >>>> doesn't have >>>> namespaces. So all the rulenames I newly define must be distinct >>>> from those >>>> defined with <attribute>. >>>> >>>> And that is true for *every* extension. And for them to be >>>> compatible with one >>>> another they all must define rulenames that are unique among them all. >>>> >>>> So effectively each one is an update. >>>> >>>> It is subtly different if I follow (4), even if I use abnf to define >>>> the syntax for my >>>> new attribute, and even if I reuse rule definitions (like >>>> <token>) from the base sdp definition. >>>> >>>>>> One thing that people sometimes forget when defining new >>>>>> attributes is that >>>> the syntax of the new attribute MUST also be valid when parsed by >>>> the "generic" >>>> attribute syntax. AFAIK there is no way in ABNF to specify that. I >>>> think that (4) >>>> comes closest. >>>>> >>>>> Yes, but this must be checked during the last call by actual humans >>>>> not some >>>> abnf parser. >>>> >>>> For now that is true. I have found such errors while doing SDP >>>> directorate >>>> reviews. >>>> >>>> Thanks, >>>> Paul >>>> >>>>> -acbegen >>>>> >>>>>> >>>>>> Thanks, >>>>>> Paul >>>>>> >>>>> >>>>> _______________________________________________ >>>>> mmusic mailing list >>>>> mmusic@ietf.org >>>>> https://www.ietf.org/mailman/listinfo/mmusic >>>>> >>>> >>>> _______________________________________________ >>>> mmusic mailing list >>>> mmusic@ietf.org >>>> https://www.ietf.org/mailman/listinfo/mmusic >>> >>> _______________________________________________ >>> mmusic mailing list >>> mmusic@ietf.org >>> https://www.ietf.org/mailman/listinfo/mmusic >> > > > > _______________________________________________ > mmusic mailing list > mmusic@ietf.org > https://www.ietf.org/mailman/listinfo/mmusic >
- [MMUSIC] 4566bis outstanding issues Ali C. Begen (abegen)
- Re: [MMUSIC] 4566bis outstanding issues Paul Kyzivat
- Re: [MMUSIC] 4566bis outstanding issues Ali C. Begen (abegen)
- [MMUSIC] SDP attribute level for disaggregated me… Marc Petit-Huguenin
- Re: [MMUSIC] SDP attribute level for disaggregate… Ali C. Begen (abegen)
- Re: [MMUSIC] 4566bis outstanding issues Ali C. Begen (abegen)
- Re: [MMUSIC] 4566bis outstanding issues Paul Kyzivat
- Re: [MMUSIC] 4566bis outstanding issues Ali C. Begen (abegen)
- Re: [MMUSIC] 4566bis outstanding issues Paul Kyzivat
- Re: [MMUSIC] 4566bis outstanding issues Fredrik Bergholtz
- Re: [MMUSIC] 4566bis outstanding issues Ali C. Begen (abegen)
- Re: [MMUSIC] 4566bis outstanding issues - Send, r… Fredrik Bergholtz
- Re: [MMUSIC] 4566bis outstanding issues - Send, r… Paul Kyzivat