Subject: RE: [dccp] Re: [MMUSIC] Two-way media with DCCP and TFRC

From: "Rosen, Brian" <[email-masked]>
Date: Mon, 4 Aug 2003 13:58:01 -0400

> So, is the right thing to do to ramp up at the beginning of the call
> to the best rate you can get, then only ramp down?  This overcomes
> Tom's concerns about probing bandwidth.
There is no point in "ramping".  You send at the rate you decide 
(however you decide).  If you have to change, you signal a change,
disrupt the flow, and change.  There isn't anything elastic here.
You send at a fixed rate.  If you don't recieve at the correct
rate you can handle a (small) amount of variation by buffering, but
mostly, you discard and hope it gets better.

Brian 

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From: Aaron Falk <[email-masked]>
Date: Mon, 4 Aug 2003 11:15:09 -0700

> mostly, you discard and hope it gets better.

Brian-

I'm concerned about the effect "sending at a fixed rate" might have on
other traffic in the network.  "Ramping", or slow start, at the
beginning of the call allows the sender to probe for the available
capacity.  Otherwise, how does the sender know what rate to start
sending at?  If he starts too high, he'll blow away a bunch of TCP
flows while he figures out his loss rate is too high.  Starting too
low will result in the minimal quality to users.  Am I missing
something here?

I do agree that, since codecs output rates are quantized, ramping down
really means jumping from one to the next lower rate.

--aaron