Emulating ADSL bandwidth shaping

Patrick Giagnocavo patrick at zill.net
Tue May 4 03:19:07 UTC 2010

Srikanth Sundaresan wrote:
> I'm trying to model ADSL access link bandwidth shaping. With a link of
> 18Mbps, I'm using a token bucket filter (tc + netem) to model 10Mbps,
> 8Mbps and 2Mbps access plans. I have a couple of questions:
> - do ISPs typically use token bucket filters with large bursts to shape traffic?
> - what kind of burst sizes and latencies/limits are typically used for
> the filter?

You will definitely have to account for latency.

For emulating cable traffic, latencies (in the USA) will be about
60-80ms to typical sites.  Burst mode in my experience occurs only for
about the first 15 seconds, then is throttled back (though not always;
seems to depend on time of day).

For DSL, I seem to recall latency being about 90-110ms (note, I haven't
used DSL in many years).  Burst mode was generally not noticeable or
available, that is, you got the same speed regardless of downloading a
1MB jpeg or a 640MB .iso  file.



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