Subject: [MMUSIC] some comments on IPV and ICE

From: Stig Venaas <[email-masked]>
Date: Wed, 19 Nov 2003 13:59:13 +0100

First of all, I haven't studied this topic much, so bare with me for
any misunderstandings.

I have some doubts regarding IPV (draft-camarillo-mmusic-alt-02.txt).
As I understand it, IPV would be useful to ipv4-only or ipv6-only
hosts, but has significant drawbacks for dual-stack hosts not
supporting it. I believe that most IPv6 hosts today, are dual-stack
and will continue to be so for some time. An exceptiom might be some
new environments like 3G networks. I think it's better to add special
requirements for the special cases, that is, require IPv6-only hosts
to support a new solution.

I think it's important to be able to express two different things in
SDP. One is a number of addresses (possibly addresses of different
address families) where the client may pick any one, the other is a
number of addresses (again possibly different families) where the
client is supposed to use all.

Unless I've misunderstood something, the latter is fine, and the
former can be done with ICE, except that there is a preferred
address. That there's a preferred address isn't a problem I think.

If indeed the alt attribute is useful in general, isn't it better
to define this separately from ICE, and have ICE refer to that?

Stig

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From: Gonzalo Camarillo <[email-masked]>
Date: Wed, 19 Nov 2003 15:17:39 +0200

Hi,

> to define this separately from ICE, and have ICE refer to that?

This is exactly what the draft does right now. You may be referring to 
an old version of that draft.

Regarding your comment about dual-stack UAs, I do not see any problem 
related to the use of IPV.

Thanks,

Gonzalo

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From: Stig Venaas <[email-masked]>
Date: Fri, 21 Nov 2003 11:02:31 +0100

Thanks Gonzalo, but I still think there are problems, see below.

On Wed, Nov 19, 2003 at 03:17:39PM +0200, Gonzalo Camarillo wrote:
[...]
> related to the use of IPV.

Wouldn't dual-stack UAs that don't support IPV try to use both
media descriptions and try to establish two connections/streams?

Isn't that also why it in section 5 of IPV says:

   It is STRONGLY RECOMMENDED that dual-stack IPv6/IPv4 hosts implement
   the IPV semantics. Dual-stack hosts that failed to implement IPV
   would need more RTTs to establish a session with a single-stack host.
   When acting as answerers, they would establish more media streams
   than needed. This could increase the session bandwidth in the first
   instants of the session, until the remote end could issue a new offer
   with only one m= line.

Since there's alreay a large number of systems that are dual-stack,
and there probably will be even more in the future, I think one
should try to avoid such a requirement.

I understand that the IPV solution is useful to single-stack systems,
but I'm afraid it will create too many problems for existing dual-stack
systems.

Stig

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From: Gonzalo Camarillo <[email-masked]>
Date: Fri, 21 Nov 2003 12:35:39 +0200

Hi,

I got the same comment during the MMUSIC presentation. I have added a 
section that defines a SIP option-tag and that explains what can happen 
in you do not use it (basically it explains what you also point out in 
your mail.)

I intend to release a new version of the draft pretty soon. I hope it 
will address all the comments that I have received from the group.

Thanks for your comments,

Gonzalo

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