[126156] in North American Network Operators' Group
Re: Emulating ADSL bandwidth shaping
daemon@ATHENA.MIT.EDU (Patrick Giagnocavo)
Mon May 3 23:19:42 2010
Date: Mon, 03 May 2010 23:19:07 -0400
From: Patrick Giagnocavo <patrick@zill.net>
To: Srikanth Sundaresan <srknth.s@gmail.com>, NANOG <nanog@nanog.org>
In-Reply-To: <r2q590586ac1005031947q63fb84abn783477577064657c@mail.gmail.com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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.
IMHO, IME, ISTR, YMMV...
--Patrick
