[e2e] High Packet Loss and TCP

[David G. Andersen]

On Thu, May 01, 2003 at 03:40:42PM -0400, Ross Callon quacked:
> My understanding is that there is some level of packet loss 
> which causes TCP to back off to the point of stopping. My 
> impression is that this is a sufficiently high loss rate that it 
> shouldn't happen in a network which is behaving properly, 
> and if it happens this should be considered a network failure 
> rather than a TCP problem. (I am pretty sure that I saw this 
> sort of behavior a few years ago when trying to access large 
> files over a very bad link). 
> 
> Is there a paper which would describe what the appropriate 
> loss rate is that would cause this problem? Is there any 
> general understanding of what level of packet loss will cause
> serious problems?

My favorite source for this is from Padhye et al., 
which shows a pretty drastic knee in the TCP performance curve
when the loss rate starts to exceed about 30%.  It's not a
total "outage", but it does represent about a two order of
magnitude reduction in throughput, and renders the network
pretty unusable.

J. Padhye, V. Firoiu, D. Towsley, and J. Kurose
Modeling TCP Throughput:  A Simple Model and its Empirical Validation.
In Proc. ACM SIGCOMM, September 1998.

ftp://gaia.cs.umass.edu/pub/Padhye-Firoiu98-TCP-throughput.ps.Z

   -Dave

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