[c-nsp] ASR9000 queue-limit ? ms

Saku Ytti saku at ytti.fi
Tue Oct 15 05:35:02 EDT 2013

On (2013-10-15 22:04 +1300), Pshem Kowalczyk wrote:

> 1. Voice - 2-3 ms (and probably a policer around 35-40% of link size)
> 2. Video - up to 10 ms (assuming HD streaming, otherwise less)
> 3. Everything else - about 5 ms

Is there platform where you can configure this?

Consider you'd have 100Mbps connection with:

10% BE
90% EF

Then you configure 5ms for EF, i.e. 90Mbps*0.005s = 56kB

Now lets imagine during office hours offered rate is fairly close to that, but
outside office hours offered load would flip otherway around, with only 10% of
Then you'd actually have 10Mbps * X = 56kB, where X would be 44.8ms.

So you'd buffer EF during office hours expected 5m and outside office hours
you'd buffer 45ms, which would probably break your EF.

Maybe the example is rather extreme, but I think it's highly typical to
observe different distribution of offered loads throughout the day. And as far
as I know, all platforms where you specify temporal number for queue will be
programmed as fixed bytes in HW.

So if you really do have variable offered rates throughout the day, you
actually need to make some compromise which will be acceptable in both
scenarios, but not perfect in either.

So I would recommend using bytes when defining buffer sizes, unless your
platform actually can do temporal buffers as function of _offered_ rate.


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