Subject: [AVT] Re: IETF 60 AVT minutes

From: "John Lazzaro" <[email-masked]>
Date: Thu, 2 Sep 2004 16:32:28 -0700

> Randell Jesup <[email-masked]> wrote:
>         TCP-friendly feedback in RTP (especially using current RTCP) 
> seems
> to have some serious issues with reverse-path bandwidth costs.  Unlike 
> TCP
> the acks are large and can't be piggybacked.  While TFRC is supposed to
> exist to "play nice" with other TCP and RTP streams (unlike raw RTP), 
> the
> additional reverse-channel bandwidth could conversely make things worse
> (overall), especially on asymmetric links or in two-way communication.

Has anyone ever sat down, examined all of the standard RTCP
fields, and defined all the stream semantic information a sender
can deduce by examining the fields of receiver packets as defined
in the RFC?  The Highest Extended Sequence Number Received
field is a good starting point, but other fields may have semantics
(as opposed to statistics) embedded in them too.

And, after writing down those constraints, has anyone asked "Can I
design a TCP-friendly feedback system that only used these fields"
under certain assumptions? And tried hard before giving up?

If not, someone should ... maybe there is a "good enough" solution
using standard RR and SR packets out there, waiting to be discovered.

---
John Lazzaro
http://inst.eecs.berkeley.edu/~cs152/
lazzaro [at] cs [dot] berkeley [dot] edu
---

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

---

From: Ladan Gharai <[email-masked]>
Date: Tue, 7 Sep 2004 15:41:06 -0400

John:

In terms of reusing the current semantics and fields of the RR and SR 
reports for the TFRC exchange of congestion control info - two field 
that could potentially be reused are the LSR and DLSR fields of the 
Reciver Reports. From section 9 of the draft:

    o  RTT calculations by the sender: As an alternative to including
       t_i and t_delay in each RTCP packet, could the sender use the LSR
       and DLSR fields of the Receiver Reports to calculate the RTT?
       This is mainly  a question of: is the frequency of the RTTs
       computed from Sender Reports sufficient for the sender to react
       to changes in the RTT and congestion?

Ladan.

On Sep 2, 2004, at 7:32 PM, John Lazzaro wrote:

>> to have some serious issues with reverse-path bandwidth costs.  
>> Unlike TCP