[c-nsp] srr-queue bandwidth share on 3750

[Peter Rathlev]

On Mon, 2009-08-31 at 16:33 -0400, samuel vuillaume wrote:
...
>  srr-queue bandwidth share 1 59 30 10
...
> In case of congestion, let's say my queue 2 is free of use
> (empty) .... How are my queues 3 and 4 gonna to use the free queue
> bandwidth queue 2? i mean, with this configuration my queue 2,3 and 4
> get the remaining bandwidth after the queue 1:
> 
> queue 2, 59/99*66Mps = 39 Mbps
> queue 3, 20Mbps
> queue 4, 6Mps
> 
> so it means 39 Mpbs available to allocate to queue 3 and Queue 4...
> how ths traffic will be shared between 3 and 4? ( i suppose it's
> related to the priority of the queue)

They will share, but not equally. Queue 3 will take 75% of the remaining
bandwidth, queue 4 will take 25%. If any queue does not use it's
allocated amount (either because it uses a shaping SRR instead or
because there are no packets) the allocation is simple disregarded.

You can view the SRR sharing algo as:

1) take W1 packets from queue 1 (=> 0, shaping)
2) take W2 packets from queue 2 (=> 0, queue empty)
3) take W3 packets from queue 3 (=> 30 if they're there)
4) take W4 packets from queue 4 (=> 10 if they're there)
5) repeat from step 1)

So each round of 40 packets takes 30 from Q3 and 10 from Q4.

-- 
Peter