[Codel] R: Making tests on Tp-link router powered by Openwrt svn

Kathleen Nichols nichols at pollere.com
Fri Dec 21 12:06:03 EST 2012

On 12/21/12 2:32 AM, Dave Taht wrote:
> On Fri, Dec 21, 2012 at 5:19 AM, Alessandro Bolletta
> <alessandro at mediaspot.net> wrote:
>> Also, i tried to decrease interval and target options in order to obtain a
>> latency, for connections estabilished while upload is flowing, lower that 5
>> ms.
>> So i set target at 2ms and interval to 5ms.
> You are misunderstanding target and interval. These control the
> algorithm for determining when to drop. interval is set to 100ms by
> default as to try to find a good estimate for the RTT, and target to
> 5ms as to have a goal for a maximum delay to aim for. These values
> work well down to about 4Mbits, at which point we have been bumping
> target up in relation to how long it takes to deliver a packet. A
> value I've been using for target at 1Mbit has been 20, as it takes
> 13ms to deliver a large packet.


Thanks for clarifying the target and interval. The notion of using a 2ms
and a 5ms interval boggles the mind and is precisely why we were looking
for parameters that the user didn't have to fiddle. Of course, it has to
be running
in the location of the actual queue!

I don't understand why you are lowering the target explicitly as the use of
an MTU's worth of packets as the alternate target appeared to work quite
well at rates down to 64kbps in simulation as well as in changing rates.
I thought Van explained this nicely in his talk at IETF.


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