RE: [AVT] Offer/answer questions on RFC 4585

Christer,

Inline

________________________________

From: Christer Holmberg [mailto:christer.holmberg@ericsson.com] 
Sent: Monday, October 01, 2007 10:11 AM
To: avt@ietf.org
Subject: [AVT] Offer/answer questions on RFC 4585

Hi,

I have a couple of questions on RFC 4585, regarding the usage with offer/answer.

My FIRST question is: are there any TECHNICAL reasons (I know it's probably not allowed by RFC 3264) why a user receiving an AVPF offer, but doesn't support it, can't reply with AVP answer (instead of rejecting the stream)? My understanding is that if you offer AVPF you still have to be able to do AVP, so...

(The receiver of course needs to understand the "AVPF" string in the SDP)

[RE:]  I think that is this case the offer  will include a=rtcp-fb with rtcp-fb-vals. Since the receiver understands AVPF but do not support any feedback message it will remove all rtcp-fb-val in the answers.

To me that looks like support of AVP so why do you want to change the avpf to avp.

My SECOND question is on example 3 in chapter 4.4. The RFC shows two m=video lines (one AVPF and one AVP) with the SAME port number (51372), and says that an appropriate grouping mechanism should be used to group the AVPF and AVP alternatives

However, I believe that even if you use some grouping mechanism, you are still not allowed to use the same port number in two m= lines. There has been much discussion about this on the MMUSIC list, but as far as I know that rule hasn't been changed. I assume this would be only an editorial bug?

[RE:] Yes

Regards,

Christer