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

From: Magnus Westerlund <[email-masked]>
Date: Wed, 02 Apr 2003 13:33:29 +0200

Hi

See below:

Timur Friedman wrote:

>Colin Perkins wrote:
>
>  
>
>>--> Magnus Westerlund writes:
>>...
>>    
>>
>>>>2.- Just curious, why are the report blocks used without signaling? It
>>>>would be helpful to include the reason for this in the draft (if it's
>>>>        
>>>>
>not
>  
>
>>>>there already and I missed it)
>>>>        
>>>>
>>>As I understand it the use case for having report blocks without
>>>signaling is that you know that you are using application foo. Foo has
>>>defined that we will use certain report blocks. Then it is not necessary
>>>to use the signaling, which may in fact not exist. Certain report blocks
>>>may be used to discover if the other end parts understand them. For
>>>example the RTT measurement can be tried a few times to see if any
>>>receiver responds to them.
>>>      
>>>
>>RTP allows applications to send new types of RTCP packet, even if these
>>    
>>
>are
>  
>
>>not explicitly signalled. RTCP XR shouldn't impose additional
>>    
>>
>restrictions.
>
>The draft will be sure to specify that SDP signalling is an optional
>mechanism, to avoid any confusion.
>
>- Timur
>
>  
>
Yes, there is a couple of different approaches here.

I agree that the usage of SDP signaling is optional. And the usage needs 
to be decided on application level. However I think that if your 
application is using SDP signaling, the signaling needs to be followed. 
Otherwise it is impossible to have meaningful signaling. For example 
take the RTT functionality. If you understand it and the arranger of a 
multicast session decides that only senders SHALL or SHOULD respond with 
DLRR packets. Unless the signaling allows us to use normative language 
to that effect the whole signaling is useless. Sending DLRR packets from 
all receiver is problem in multicast groups. Therefore there is need for 
using SHOULD or SHALL in the signaling description.

However there seem to be need to clarify that the usage of the signaling 
is optional and depends on the application.

Any comments on this?

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]

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

---

From: "Timur Friedman" <[email-masked]>
Date: Wed, 2 Apr 2003 21:24:25 +0200

> application is using SDP signaling, the signaling needs to be followed.

Agreed that if the application is using SDP signalling and XR packets then
it must adhere to the SDP signalling mechanism defined for XR packets.
We'll be sure to state this.

- Timur Friedman