Subject: RE: draft-olson-sdp-ipv6-02.txt

From: "Christian Huitema" <[email-masked]>
Date: Thu, 11 Oct 2001 17:56:00 -0700

> Something like:
> 
> C=IN IP4or6 131.160.1.112[3ffe:1200:3012:c006:290:27ff:fe7d:d024]

Tempting, but it fails for two reasons. First, solutions such as
modified C lines or duplicated C lines break interoperability with
un-reconstructed v4-only nodes; you don't want that. Second, the port
used over IPv4 may not be the same as over IPv6; this is almost always
the case if your IPv4 connection goes through a NAT. If we go that way,
then I would rather use something like:

        m=audio 30000 RTP/AVP 0 
        c=IN IP4 131.160.1.112
        a=altC:20000:IN IP6 3ffe:1200:3012:c006:290:27ff:fe7d:d024

I.e. use an attribute, and document both the port and the address.

-- Christian Huitema

---

From: Christer Holmberg <[email-masked]>
Date: Fri, 12 Oct 2001 08:34:45 +0300

Hi,

Instead of defining mechanisms to make message shorter, but which only
works for this specific case, I think we should look at this from a more
general point of view. 

First, it's not only about the address. We may also have separate
attributes, which may have different values depending on if they are for
IP4 or IP6. In that case we would have to use "a=altC:a=<whatever>" for
those.

Second, now we are only talking about "IP4 vs IP6" for a session, but in
future there MAY be scenarios where we have IP, ATM, and who knows what
- in all kind of "choose-one-of-these-for-the-session" combinations...

Regards,

Christer Holmberg
Ericsson Finland

---

From: Pekka Pessi <[email-masked]>
Date: 25 Oct 2001 13:44:48 +0300

>IP4 or IP6. In that case we would have to use "a=altC:a=<whatever>" for

	I agree on these, so a group attribute seems to be a superior
	solution for the dual-stack problem.  However, the current FID
	semantics are not exactly what we want.  Should we define a new
	group semantics like "ALT" (see below)?  

					Pekka

v=0
o=- 38973621 6 IN IP6 3ffe:1200:3012:c006:290:27ff:fe7d:d024
s= 
a=group:ALT ip4 ip6
m=audio 6000 RTP/AVP 96 97 99
c=IN IP6 3ffe:1200:3012:c006:290:27ff:fe7d:d024
a=mid:ip6
a=rtpmap:97 AMR/8000
a=fmtp:97 mode-set=4,5,6 interleaving crc vad=on use-redundancy=1
a=rtpmap:99 AMR/8000
a=fmtp:99 mode-set=8
a=rtpmap:96 AMR-WB/16000
m=audio 6000 RTP/AVP 96 97 99
c=IN IP4 172.21.40.44
a=mid:ip4
a=rtpmap:97 AMR/8000
a=fmtp:97 mode-set=4,5,6 interleaving crc vad=on use-redundancy=1
a=rtpmap:99 AMR/8000
a=fmtp:99 mode-set=8
a=rtpmap:96 AMR-WB/16000

---

From: Pekka Pessi <[email-masked]>
Date: 25 Oct 2001 14:05:21 +0300

Hello,

	The sdp-new-03 draft does not explicitly say if rtpmap is a
	media-level attribute.  Should it be stated, or is it clear from
	context?  Should there be a separate paragraph describing rtpmap
	like other attributes?

						Pekka

---

From: Colin Perkins <[email-masked]>
Date: Thu, 25 Oct 2001 18:39:29 -0400

>	context?  Should there be a separate paragraph describing rtpmap

It should probably have a separate paragraph, to be consistent. I'll see 
what I can do with the next version.

Cheers,
Colin