[Iccrg] Re: Appropriate rate given corruption
michael.welzl at uibk.ac.at
Mon Aug 27 07:22:50 BST 2007
On Sun, 2007-08-26 at 16:16 -0700, Lachlan Andrew wrote:
> Greetings Michael,
> Our previous discussion on the appropriate rate for congestion control
> in the presence of corruption got a bit stuck on details. If you
> have the time, I'd like to try again, starting with some things I
> think we can agree on.
Okay - I think that's a good approach, thanks!
> Do you agree that
> 1. TCP responds with a rate approximately K/sqrt(p) where K is a
> constant dependent on such things as RTT and packet size, and p is
> the total loss probability
> 2. On a path with multiple bottlenecks, with loss rates p_i, the
> total loss rate is slightly less than the sum of the p_i. That
> is, p = 1-product(1-p_i) < (sum p_i)
First of all, the way I think about it, there is only one
bottleneck along a path per definition (so the p_i's will
all be close to zero except for one of them, which
represents the bottleneck).
Secondly, I don't understand why the total loss rate of
the path would be slightly less than the sum of the p_i
and not precisely that sum.
> 3. As a result, TCP gives slightly higher rate to multi-hop flows
> than a hypothetical scheme which gave a rate K/sqrt(sum p_i) <=
No because this is based on 2, which I disagree with.
> 4. (More of a stretch) Consider a network only one link l_0 which
> corrupts packets, which transmits fraction r of the packets it
> receives. Then each received packet on a flow traversing l_0
> creates as much additional congestion as a flow in a modified network
> such that
> (a) there is no loss
> (b) each link l_i upstream of l_0 is replaced by "1/r" links,
> each with the same amount of congestion as l_i had in the original
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