Re: [MMUSIC] Connection Data Capability (ccap) and IP-addresses (draft-ietf-mmusic-sdp-miscellaneous-caps-04)

Flemming Andreasen <fandreas@cisco.com> Sun, 24 March 2013 15:39 UTC

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Date: Sun, 24 Mar 2013 11:39:21 -0400
From: Flemming Andreasen <fandreas@cisco.com>
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To: Christer Holmberg <christer.holmberg@ericsson.com>
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Cc: Jonathan Lennox <jonathan@vidyo.com>, "mmusic@ietf.org" <mmusic@ietf.org>
Subject: Re: [MMUSIC] Connection Data Capability (ccap) and IP-addresses (draft-ietf-mmusic-sdp-miscellaneous-caps-04)
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On 3/23/13 5:24 AM, Christer Holmberg wrote:
> Hi,
>
> In general I agree that having multiple ways of doing the same thing is not a good thing, and I don't have any strong feelings regarding the ccap usage.
>
> But, no matter what we say, what would actually prevent people from using ccap, in the same way they are using ANAT and altc? :)
There's no port signaling capability with ccap, but other than that, the 
only thing that prevents people from using this to signal alternative 
IP-addresses is the existence of a "MUST NOT" in the spec.

-- Flemming

> Regards,
>
> Christer
>
>
> ________________________________________
> From: mmusic-bounces@ietf.org [mmusic-bounces@ietf.org] on behalf of Jonathan Lennox [jonathan@vidyo.com]
> Sent: Friday, 22 March 2013 10:00 PM
> To: Flemming Andreasen
> Cc: mmusic@ietf.org
> Subject: Re: [MMUSIC] Connection Data Capability (ccap) and     IP-addresses    (draft-ietf-mmusic-sdp-miscellaneous-caps-04)
>
> Currently, the deployed SIP world has three mechanisms to allow some flavor of negotiation among multiple IP addresses: ICE, altc (despite the general disapproval of the working group), and ANAT (despite its deprecation).
>
> I think that adding ccap as a fourth member of this set would be a terrible idea; and as far as I can tell, no one wants to do that.  So we need to make it clear that that it MUST NOT be used for that purpose.
>
> In the formulation below, I think I'd say that a given media description MUST NOT indicate more than one address with an IN network type, across all its configurations (actual and potential).
>
> Obviously, different media descriptions (m= line blocks) can have different addresses.
>
> In practice, given the port number issue that started this thread, I suspect this means that the SDP offer will need to put the IN address in the actual configuration (in the c= line), and the PSTN address(es) will be in the potential configurations.
>
> On Mar 22, 2013, at 2:37 PM, Flemming Andreasen wrote:
>
>> Still waiting for more comments on this, especially from the people that
>> were very vocal in their complaints previously: Now is the time to speak up.
>>
>> Regardless, a few comments on the below:
>> 1) It allows the use of "ccap" to be used to indicate one or more "IP4"
>> addresses in a given SDP.
>> 2) It allows the use of "ccap" to be used to indicate one or more "IP6"
>> addresses in a given SDP.
>>
>> Nit-picking a bit on the actual text, which I think is important:
>> The "ccap" attribute is not what is being to select between different
>> IP-addresses; the use of a "ccap" attribute in a potential configuration
>> ("pcfg") is what is being used for this. Is the restriction that we want
>> here:
>> a) A potential configuration MUST NOT reference more than one "ccap"
>> attribute with a network type of "IN" ?
>> b) All potential configurations for a particular media description MUST
>> NOT reference more than one "ccap" attribute with a network type of "IN" ?
>> c) Something else ?
>>
>> Thanks
>>
>> -- Flemming
>>
>>
>>
>> On 3/22/13 1:35 AM, Andrew Allen wrote:
>>> I am OK with either of these proposals
>>>
>>> -----Original Message-----
>>> From: mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] On Behalf Of Simo.Veikkolainen@nokia.com
>>> Sent: Wednesday, March 20, 2013 5:57 AM
>>> To: fandreas@cisco.com; mmusic@ietf.org
>>> Subject: Re: [MMUSIC] Connection Data Capability (ccap) and IP-addresses (draft-ietf-mmusic-sdp-miscellaneous-caps-04)
>>>
>>> I went through the discussion, and my reading is that there is agreement on not allowing ccap to be used for alternative IP address negotiation.
>>>
>>> That could be made clear in the text e.g. by modifying the second sentence Flemming quoted to read:
>>>
>>> <quote>
>>>      The 'ccap' attribute MUST NOT be used to select
>>>      between different IP connection addresses (e.g. between
>>>      "IP4" and "IP6" address families or different IP addresses
>>>       within the same IP address family).
>>> </quote>
>>>
>>> The ccap attribute should be able to carry either an IP or PSTN address; that way either a PSTN or an IP bearer could be offered as the highest priority configuration (in the "m=" line).  However, if we want to clarify the intended use of ccap, we could modify the first sentence to read:
>>>
>>> <quote>
>>>     The 'ccap' capability attribute is intended for offering
>>>     alternative connection addresses where the <nettype>
>>>     is "IN" or "PSTN", i.e. selecting between an IP based
>>>     bearer or a circuit-switched bearer.
>>> </quote>
>>>
>>> Simo
>>>
>>> -----Original Message-----
>>> From: mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] On Behalf Of ext Flemming Andreasen
>>> Sent: 19. maaliskuuta 2013 8:24
>>> To: mmusic
>>> Subject: [MMUSIC] Connection Data Capability (ccap) and IP-addresses (draft-ietf-mmusic-sdp-miscellaneous-caps-04)
>>>
>>> Greetings
>>>
>>> As you may have seen, there has recently been some list discussion on the "connection data capability" defined in
>>> draft-ietf-mmusic-sdp-miscellaneous-caps-04 (see e.g. thread in
>>> http://www.ietf.org/mail-archive/web/mmusic/current/msg10472.html)
>>>
>>> To recap, the connection data capability ("ccap") provides capability negotiation capabilities for what amounts to the "c=" line in regular SDP, and as such enables negotiation of network type (such as "IN") and IP-address information (v4 and v6 addresses). The Standards Track mechanism for negotiating and determining alternative IP-address information today is ICE, and hence the draft currently includes the following wording:
>>> <quote>
>>> The 'ccap' capability attribute is intended to
>>>      be used only when there is no other mechanism available for
>>>      negotiating alternative connection address information, such as when
>>>      the <nettype> is different among the alternative addresses (e.g.
>>>      "IN" and "PSTN").  The 'ccap' attribute MUST NOT be used in
>>>      situations where an existing mechanism (such as Interactive
>>>      Connectivity Establishment (ICE) [RFC5245]) can be used to select
>>>      between different connection addresses (e.g.  "IP4" and "IP6" or
>>>      different IP addresses within the same IP address family).
>>> </quoted>
>>>
>>> The above text has led to some confusion as to exactly when and what "ccap" can be used for. More specifically, is it/should it ever be allowed to use "ccap" to convey an IP4 or IP6 address, and if so, under what circumstances ?
>>>
>>> If you have an opinion, please let us know.
>>>
>>> A couple of points to keep in mind:
>>> - The current document has been WGLC'ed without comment ~6 months ago.
>>> - 3GPP has a dependency on the document (however I'm not sure if that dependency includes the above "IN" feature)
>>> - The connection data capability is defined in a general manner to be generally useful in line with the overall capability negotiation framework (as opposed to targeted at one specific use case with one specific value)
>>> - There are scenarios where ICE cannot be used, even if implemented (e.g. ice-mismatch).
>>> - RFC 6849 (media loopback) provides for NAT traversal in the absence of ICE support
>>>
>>>
>>> Thanks
>>>
>>> -- Flemming
>>>
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> --
> Jonathan Lennox
> jonathan@vidyo.com
>
>
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