Re: [MMUSIC] RE : I-D Action: draft-ietf-mmusic-sdp-miscellaneous-caps-04.txt

Flemming Andreasen <> Thu, 14 March 2013 19:45 UTC

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Date: Thu, 14 Mar 2013 15:45:35 -0400
From: Flemming Andreasen <>
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Subject: Re: [MMUSIC] RE : I-D Action: draft-ietf-mmusic-sdp-miscellaneous-caps-04.txt
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As to ccap not being an alternative to ICE we are all in agreement on 
that - the lack of port negotiation alone makes that clear (it simply 
doesn't work without that).

As to ccap being explicitly forbidden to express IP4 and/or IP6 
addresses as alternatives, can somebody please point me to either 
meeting minutes or mailing list discussion to that effect ? The only 
thing I have found is the port discussion we had in Taipei, where we 
agreed not to add a port capability. From

Miscellaneous Capabilities Negotiation in SDP (Simo Veikkolainen, 10)



Simo presented hisslides 

Simo explained the need to be able to indicate alternative port numbers, 
but PSTN media, port number doesn't make sense. The CS draft says use 
port number 9 (the discard port). We have to put something there because 
required by SDP syntax. If an RTP stream is offered, then a regular port 
number should be written instead. The problem arises when both CS and 
RTP streams are offered at the same time, one as an alternative of the 
other. Then, the port number makes sense for RTP but not for CS, but 
still, there is a single place to write the port number in the SDP, so, 
has to be shared by both alternative media streams.

Possible solutions:

1. Circuit-switched media uses the same port as RTP media even though 
the port is not really used

2. Extend capneg with a port number capability attribute, restricting 
its use to cases where ICE cannot be used.

3.Select anything as a port number and say "do not care on reception".

Jonathan Lennox suggested saying that port numbers not equal 0 have to 
be ignored.

Hadriel Kaplan asked if middle boxes not supporting this stuff can be 
broken. The discussion is moved offline.

There are questions on how could be possible to indicate preference for 
one media stream above the alternative.

Miguel Garcia suggested using port 9 if it works. If not take anything 
not equal 0. Receiver has to ignore.

In general, there was pushback on the port negotiation approach. The 
authors should explore a solution along the third option: write the RTP 
port number in the "m=" line. If CS alternative is chosen, discard the 
port number on reception.

Apart from that, the only thing I'm aware of is the 4 WG versions of 
this draft which have all said the same about IP4/IP6 and ICE, and 
again, that text was both WGLC'ed and reviewed by 2 volunteers without 
any concerns. Where does the alternate understanding come from ?


-- Flemming

On 3/14/13 2:16 PM, Stach, Thomas wrote:
> This is also my understanding
> ... although my initially proposed text does not reflect this correctly.
> Regards
> Thomas
>     ------------------------------------------------------------------------
>     *Von:* []
>     *Im Auftrag von *Andrew Allen
>     *Gesendet:* Donnerstag, 14. März 2013 14:10
>     *An:*;
>     *Cc:*
>     *Betreff:* Re: [MMUSIC] RE : I-D Action:
>     draft-ietf-mmusic-sdp-miscellaneous-caps-04.txt
>     My understanding also was that we agreed that CCAP was not an
>     alternative to ICE.
>     *From*: Jonathan Lennox []
>     *Sent*: Thursday, March 14, 2013 01:06 PM Central Standard Time
>     *To*: Flemming Andreasen <>
>     *Cc*: <>;
>     Andrew Allen; <>
>     *Subject*: Re: [MMUSIC] RE : I-D Action:
>     draft-ietf-mmusic-sdp-miscellaneous-caps-04.txt
>     On Mar 14, 2013, at 1:43 PM, Flemming Andreasen wrote:
>>     On 3/14/13 11:40 AM, wrote:
>>>     Re-,
>>>     What is important is the quality of produced documents. The
>>>     content of the document is not frozen and unless I'm mistaken
>>>     there is not IETF LC.
>>     Correct.
>>>     What I understand from the text in the draft is: ccap is allowed
>>>     to signal an IPv4@ and IPv6@ if ICE is not supported.
>>     ccap is not prohibited from doing so in the absence of ICE,
>>     however as explained in the document
>>     1) When the IETF Standard Track mechanism ICE is available, ccap
>>     MUST NOT signal an IPv4/IPV6 address alternative.
>>     2) The draft does (intentionally) not provide a full solution for
>>     negotiating alternative IP-addresses since we have a Standards
>>     Track mechanism for doing so (ICE).
>     Hi, Fleming --
>     My understanding of the WG consensus -- and my interpretation of
>     the text in the draft -- was stronger than this: ccap MUST NOT be
>     used for the kinds of alternatives ICE can express, whether or not
>     ICE is actually being used in a particular offer/answer.
>     If we're getting divergent interpretations of this document, we
>     probably do need to update its text.
>     --
>     Jonathan Lennox
> <>
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