why upload with adsl is faster than 100M ethernet ?

Alex Bligh alex at alex.org.uk
Fri Oct 15 12:24:36 UTC 2004



--On 15 October 2004 13:33 +0200 Iljitsch van Beijnum <iljitsch at muada.com> 
wrote:

> However, the cause can also be rate limiting. Rate limiting is deadly for
> TCP performance so it shouldn't be used on TCP traffic.

Add "unless appropriate shaping is performed prior to the rate-limiting
with the parameters carefully tuned to the rate-limiting"

You can also see an effect similar to rate-limiting from inadequate
buffering where there is a higher input media speed than output.

I can't remember what the tool is now, but there used to be a tool which
worked like ping but sent a udp stream at a given rate per second and told
you about packet drops, and also allowed for some parameter to be tweaked
to give stochastic variation in interpacket delay (i.e. massive jitter).
You could use this to show inadequate buffering on gigabit interfaces where
a 2Mb/s stream would get through, but if you wound up the jitter
sufficiently, a whole burst of packets would arrive together and a gigabit
interface with (deliberately) misconfigured buffers would then drop packets.

Alex



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