On 2/28/07, Gorry Fairhurst <gorry@xxxxxxxxxxxxxx> wrote:
2) Ian - In section 4.3 of RFC3448 we have the equation for X as:
If (p > 0)
Calculate X_calc using the TCP throughput equation.
X = max(min(X_calc, 2*X_recv), s/t_mbi);
I have been doing experiments where I deliberately drop real-time
packets when I don't believe they will get to the other end before an
expiry time. What happens though is that I can't then transmit packets
later on due to the above equation as in practice it becomes
X=2*X_recv and X_recv quickly goes close to 0 as it is the receive
rate since last feedback. Feedback gets sent once per RTT I think and
so if you don't send anything for one RTT you get X=s/t_mbi in effect
which is 530/64 for my size packets - i.e. a sending rate of 10 bytes
per second. In practice I don't get quite this bad as I don't drop off
transmitting that long usually but I still definitely get penalised.
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After reading the draft 0.2 of TFRC faster restart I think that will
solve many of my issues and issues other people will face.
The question is whether the existing TFRC should be amended or whether
people should just go ahead and implement TFRC faster restart. Either
way I suspect TFRC faster restart would end up being the default.
Ian
--
Web: http://wand.net.nz/~iam4
Blog: http://iansblog.jandi.co.nz
WAND Network Research Group
