Subject: [AVT] RE: [AVT]RE:[AVT]RE:Clarificationson[AVT]Sequenceissuewithdraft-ietf-avt-rtp-selret-04.txt

From: [email-masked]
Date: Tue, 9 Jul 2002 14:28:17 -0500

Jose,

[Jose]
> 
> The issue is that we could not provide any sufficently 
> reliable performance
> numbers until the latest version of the feedback profile draft became
> available (stable). We are now working on some performance numbers.

[David]
Thanks. Let's wait for your performance evaluation results to go on with this discussion on the efficiency of the selective payload format.

> [Jose]
> There was a mistake from my side here: what I meant to say is 
> that every
> time you need to send multiple FCI (PID+BLP) fields, you must 
> create a new
> feedback message and append it in the RTCP report. So if you 
> need to report
> more than 17 losses, e.g. 20, the profile specific extension 
> would comprise:
> 16+ 16 = 32 bytes and not 16 + 4 ( 4 for 2nd FCI) as I 
> understand from your
> comments about the RTCP length field. This overhead increases 
> in steps of 16
> bytes ; under constant bandwidth this means an increase of 
> the reporting
> interval, which may cause the feedback to be useless.
> 

[David]
The overhead should increase in steps of 4 bytes and not 16 bytes.
As commented by Joerg in a separate thread: "We can allow multiple FCIs of the same type (which Iwill put in); of course, they cannot be mixed."

[Jose]
> As you say David. "When a packet is sent for the first time and
> stored for possible retransmission, you just need to store a flag
> indicating the packet priority."
> 
> In selret this flag is contained already in the RTP packet. 
> You do not need
> any external mechanism to store and reference (packet<->flag) this
> information.
> 
> For some implementations/implementers (like us) this is an 
> simplification.
> 

[David]
Jose, having to create, transmit and store a payload header and having to parse it later is in no way simpler than storing a flag with this packet for that purpose. 

Regards, David. 

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