[cisco-bba] Can you run PQ/CBWFQ on 3640 Ethernet IF?

Dennis Peng dpeng at cisco.com
Mon Jul 28 14:11:49 EDT 2003

Paul Plantinga [p.plantinga at ee.wits.ac.za] wrote:
> Thanks, thought that was why, so I've got a traffic generator (producing a
> mixed stream of approx 1000byte tcp frames and 100b voice) and have been
> able to force a lot of packet drops on my queues.
> Assuming I am able to load the interface sufficiently to require congestion
> control is CBWFQ/PQ sufficient to reduce voice packet delay (do I need to
> Frag/Interleave, or do PQ on the input interface since the generator puts
> all traffic through the one input port) ?

PQCBWFQ (ie LLQ) should be sufficient. Fragmentation/interleaving is
only supported on PPP interfaces, so you won't be able to use it on
the LAN. But the serialization delay is low enough on a LAN that it
should not matter.


> Has anyone done any of this on the
> 3640 and ethernet?
> Anyway, I seem to be getting good matching, just to fiddle with things. Your
> thoughts are much appreciated.
> > Queuing will only have a noticeable effect if packets build up in the
> > queue. Without a sizeable queue to actively manage, any sort of fancy
> > queueing is equivalent to FIFO. Usually packets will only build up if
> > packets are being routed to an outbound interface at a sustained rate
> > greater than the interface can transmit at. This usually occurs for
> > low-speed links like serial interfaces and not so much for LAN
> > interfaces like ethernet. Not to say you couldn't overload a ethernet
> > interface, just that it is less common. You can look at the output
> > queue in "show interface". If the output queue is usually 0/40, then
> > you aren't building up packets in the queue and any type of queueing
> > will have essentially no effect.
> >
> > Dennis
> >
> > Paul Plantinga [p.plantinga at ee.wits.ac.za] wrote:
> > > Hello,
> > >
> > > I'm fairly new to this but am running IOS 12.1(5)T on a cisco3640 and am
> trying to implement some/any priority queueing of my voice on a 10Mg
> Ethernet IF. It seems that you can configure anything.. but that doesn't
> mean it will run, so from the release notes it appears I cannot do CBWFQ or
> PQ on this interface, however the Cisco feature navigator says I can. I
> tried to test them both and it seems that they are matching correctly and
> being queued correctly but changing the voice class queue limit seems to
> have no effect on the delay of my udp packets (i.e. they are being queued
> behind the tcp no matter?). So are the config commands being ignored? (but
> my packet losses indicate some effect in changing queue limit).
> > > Ultimately, what form of PQ can I run for voice in my setup?
> > >
> > > Regards
> > > Paul
> >
> > > _______________________________________________
> > > cisco-bba mailing list
> > > cisco-bba at puck.nether.net
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> >

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