Subject: Re: [AVT] SDP signaling for RTCP XR format

From: "Timur Friedman" <[email-masked]>
Date: Wed, 2 Apr 2003 21:34:24 +0200

Magnus Westerlund wrote:

> Here one issue actually surface. Is it the right thing to restrict a
> receiver to not send DLRR report block unless the usage has been
> explicitly signaled in multicast? The reason why I see a need to
> restrict it is the potential to create enormous report blocks in large
> multicast groups. And the only result is that the different receivers
> will determine there RTT to other receivers which seems to be rather
> pointless in most application. It seems that you would in fact like to
> control this operation to a few different operation modes in multicast.
> 1. fully meshed, both senders and receivers return DLRR blocks.
> 2. Sender only, only senders return DLRR blocks.
> 3. functionality off, no one responds with DLRR blocks.
>
> Should we define such a distinction in the signaling?

I agree that the signalling should allow each of these modes.  But also the
mode in which certain receivers calculate RTTs amongst themselves.  While
many applications might not use this mode, we do not want to unnecessarily
rule it out.

Here are two examples of when the mode could be used.  First, receivers
might measure RTTs amongst themselves as a prelude to some of them becoming
senders (multicast "repair servers", retansmitting lost packets, for
instance). Second, a network monitoring tool might wish to measure its RTT
to certain receivers.

- Timur Friedman

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

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From: "Alan Clark" <[email-masked]>
Date: Fri, 11 Apr 2003 17:04:14 -0400

Timur, Colin, Steve

At the recent IETF meeting we agreed that the existing draft was getting fairly stable - there were some good detail points brought up during the AVT discussion however these were easily accomodated.  

We also agreed at the AVT meeting to include some simple SDP signaling at Magnus' request however felt at the time that this would be fairly straightforward and would not take much time.  The discussion on SDP appears to be getting much more involved than anticipated and there is no apparent end in sight.  

I would like to propose that we move to a final draft without SDP in order that we can reach closure.  In San Francisco we discussed the idea of creating a separate document to describe the use of SDP for negotiating reporting/ feedback for RTP XR, RTCP and other mechanisms.  This was suggested precisely because of some concern that the negotiation mechanism could get complex and that there were a wider variety of scenarios than anticipated .. which appears to be the case.

Regards

Alan Clark

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of Timur
Friedman
Sent: Wednesday, April 02, 2003 2:34 PM
To: Magnus Westerlund; Jose Rey
Cc: IETF AVT WG
Subject: Re: [AVT] SDP signaling for RTCP XR format

- Timur Friedman

---

From: Colin Perkins <[email-masked]>
Date: Sat, 12 Apr 2003 15:46:13 -0400

Alan,

--> "Alan Clark" writes:
>At the recent IETF meeting we agreed that the existing draft was getting
>fairly stable - there were some good detail points brought up during the
>AVT discussion however these were easily accomodated.  
>
>We also agreed at the AVT meeting to include some simple SDP signaling at
>Magnus' request however felt at the time that this would be fairly
>straightforward and would not take much time.  The discussion on SDP
>appears to be getting much more involved than anticipated and there is no
>apparent end in sight.  
>
>I would like to propose that we move to a final draft without SDP in order
>that we can reach closure.  In San Francisco we discussed the idea of
>creating a separate document to describe the use of SDP for negotiating
>reporting/ feedback for RTP XR, RTCP and other mechanisms.  This was
>suggested precisely because of some concern that the negotiation mechanism
>could get complex and that there were a wider variety of scenarios than
>anticipated .. which appears to be the case.

We should certainly consider this, as one way of meeting the ITU deadline.
Before we go down this path, though, I'd like to see some discussion of the
use cases for RTCP XR packets: in which scenarios is the signalling needed?
If typical scenarios require signalling, then we have no choice but to move
forward with the SDP extensions and their integration with SIP/RTSP. On the
other hand, if signalling is only required in unusual cases, it is much
easier to separate into a new draft.

Regards,
Colin

---

From: "Alan Clark" <[email-masked]>
Date: Sat, 12 Apr 2003 20:26:15 -0400

Colin,

Excellent advice - I'll put some thoughts together this weekend.

Regards

Alan

-----Original Message-----
From: Colin Perkins [mailto:[email-masked]]
Sent: Saturday, April 12, 2003 3:46 PM
To: [email-masked]
Cc: 'Timur Friedman'; 'Stephen Casner'; 'Magnus Westerlund'; 'IETF AVT
WG'

Alan,

Regards,
Colin

---

From: Magnus Westerlund <[email-masked]>
Date: Mon, 14 Apr 2003 10:46:29 +0200

Hi,

Back in the office, I have continued my work on updating the XR format 
text.

>easier to separate into a new draft.

I have one use case for the SDP signaling. This is the 3GPP streaming 
 service (PSS). There exist different releases which include different 
functionality and some of that functionality is optional. In Release 6 
of PSS there is a proposal for bit-rate adaptation based on RTCP 
feedback and server decision. It is proposed that as a part of the 
adaptation functionality some of the XR blocks should be used. In this 
case it is very useful for a server to tell the client that it desires 
the client to send XR blocks and which. In that way the client avoids 
having to try to guess or infer that it shall send the XR blocks or not.

Best Regards

Magnus Westerlund 

Multimedia Technologies, Ericsson Research ERA/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: [email-masked]

---

From: "Alan Clark" <[email-masked]>
Date: Mon, 14 Apr 2003 10:53:18 -0400

My concern is that, whilst there may be some examples of scenarios which
would benefit from SDP signalling, is the identification of all such
scenarios and the discussion of their issues and ramifications for RTCP XR
going to be an unbounded and indefinite discussion?

Originally we agreed to put a simple SDP signalling definition in by way of
example - this seems to have been extended into a more general discussion.

Can we establish a firm goal for either completing the SDP text or deciding
that the number of scenarios warrants a separate discussion/draft?

Alan

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of Magnus
Westerlund
Sent: Monday, April 14, 2003 4:46 AM
To: Colin Perkins
Cc: 'IETF AVT WG'
Subject: Re: [AVT] SDP signaling for RTCP XR format

Hi,

Best Regards

Magnus Westerlund

---

From: Colin Perkins <[email-masked]>
Date: Mon, 14 Apr 2003 11:35:25 -0400

Alan,

I'm not so concerned about the number of scenarios, but rather those that
we expect to be commonly used. How do you expect RTCP XR to be used? 

Colin

---

From: "Alan Clark" <[email-masked]>
Date: Mon, 14 Apr 2003 11:52:14 -0400

Colin

I expect that one of the major uses of RTCP XR would be to support the fault
and performance management of IP phones, addressing both enterprise and
carrier applications, and potentially residential gateways that support
VoIP.   There is a strong need within the industry for a low cost means of
monitoring user perceived quality - this can be very economically
implemented using RTCP XR.  There are specific cases, for example IP
Centrex, where the absence of an RTCP XR-like protocol is severely impacting
the ability of service providers to detect problems that affect user
perceived quality and hence is affecting the speed with which these services
are deployed.

I certainly don't regard RTCP XR as a research or experimental tool, but as
a protocol that has some very real and immediate applications that will help
to speed deployment of VoIP.  I am also the editor for several emerging TIA
standards related to VoIP CPE management and have already introduced the
RTCP XR draft to the group as forming a good basis for our work.

Regards

Alan Clark

-----Original Message-----
From: Colin Perkins [mailto:[email-masked]]
Sent: Monday, April 14, 2003 11:35 AM
To: [email-masked]
Cc: 'Magnus Westerlund'; 'IETF AVT WG'
Subject: Re: [AVT] SDP signaling for RTCP XR format

Alan,

Colin

---

From: Magnus Westerlund <[email-masked]>
Date: Mon, 14 Apr 2003 18:06:47 +0200

Hi,

When I wrote the SDP section I have considered the following use cases:

- RTSP controlled streaming.
- Mbone type lecture session with extra feedback.
- SIP controlled conversational sessions. Two parties.

Are there any more that we really need to consider? I would imagine that 
some more obscure cases may also very well work. The SIP case may be the 
weakest as I don't have practical experience of SIP/SDP. So I would 
really appreciate review by someone that has that background.

Best Regards

Magnus

-- 

Magnus Westerlund