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

<Simo.Veikkolainen@nokia.com> Mon, 08 April 2013 06:35 UTC

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From: <Simo.Veikkolainen@nokia.com>
To: <fandreas@cisco.com>, <aallen@blackberry.com>, <HKaplan@acmepacket.com>
Thread-Topic: [MMUSIC] Connection Data Capability (ccap) and IP-addresses (draft-ietf-mmusic-sdp-miscellaneous-caps-04)
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Date: Mon, 8 Apr 2013 06:35:24 +0000
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Cc: jonathan@vidyo.com, mmusic@ietf.org, christer.holmberg@ericsson.com
Subject: Re: [MMUSIC] Connection Data Capability (ccap) and IP-addresses (draft-ietf-mmusic-sdp-miscellaneous-caps-04)
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Recapping the discussion so far:


- ICE is the way to negotiate between different IP addresses. There seems to be no disagreement here.

- since no alternative port number can be expressed, in practice the IN address needs to go to the actual configuration (address in the c= line and port number in the m= line), and the alternative PSTN address in the potential configurations. Also here, there seems to be no disagreement.

- then, whether the "ccap" attribute should be limited to carry only PSTN addresses, or also other types. I'm with Flemming on this one; SDP capneg framework is already fragmented enough, and limiting the connection address capability to PSTN addresses only would again be targeted for a single use case only, whereas we should strive for general solutions. 

Simo


-----Original Message-----
From: mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] On Behalf Of ext Flemming Andreasen
Sent: 25. maaliskuuta 2013 3:32
To: Andrew Allen
Cc: jonathan@vidyo.com; mmusic@ietf.org; christer.holmberg@ericsson.com
Subject: Re: [MMUSIC] Connection Data Capability (ccap) and IP-addresses (draft-ietf-mmusic-sdp-miscellaneous-caps-04)


On 3/24/13 1:33 PM, Andrew Allen wrote:
> There is also nothing that prevents people from defining their own proprietary attributes to do such a thing but that is not part of an IETF standard and is not approved usage.
Agreed.

> If we really feel the need to discourage further such usage I suppose we could add some text stating that if CCAP s received containing an IN net  type and an IN net type is present in the corresponding Connection Attribute then the CCAP attribute MUST be ignored.
I think that gets complicated quickly for a questionable gain. I'd 
prefer the "MUST NOT" described below with an explanation as to why it's 
there; as you note, ultimately people either decide to be spec compliant 
or not.

-- Flemming
> That way compliant implementations would not perfom the discouraged behavior.
>
> Andrew
>
> ----- Original Message -----
> From: Flemming Andreasen [mailto:fandreas@cisco.com]
> Sent: Sunday, March 24, 2013 10:39 AM Central Standard Time
> To: Christer Holmberg <christer.holmberg@ericsson.com>
> 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)
>
>
> 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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