[j-nsp] Output queue drops and temporal buffers

[Christopher E. Brown]

On 10/1/2013 11:12 AM, John Neiberger wrote:
> 
> My question regarding the config is this: if we are already setting the
> transmit rate percentage, why would we also configure a temporal
> allocation? Isn't a percentage of the available bandwidth sufficient? What
> does adding a temporal allocation buy us? Is the transmit rate percent just
> setting how often that queue is serviced, while the buffer-size configures
> the queue depth?
> 
> Thanks,
> John


transmit rate is how fast you empty the buffer (if not constrained and excess avail may
empty faster)

Buffer size is just that.


If you do not set IIRC the available buffer is divided among the queues by transmit rate.

This is fine, but the available buffer may be very large compared to how much delay you
want to allow in a class.


EF traffic should not be buffered more than a very small amount, if you cannot send in 2ms
or less you really need to drop it.

Even for the BE queue, how much latency climb do you want to allow before you start
dropping?  200ms is insane, 10ms is too small, something in the 40 - 80 ms range would be
better (or maybe much larger on a small long haul pipe).


Now, you can get all this by setting explicit buffer sizes, BUT those sizes are tailored
toa specific transmit rate.

What if you want to run the same core maps on OC3, OC12, 1GE, 10GE?  You need to set
transmit rate percent and buffer temporal...  Scales to the actual rate to provide just
enough but not too much buffering.


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Christopher E. Brown   <chris.brown at acsalaska.net>   desk (907) 550-8393
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