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

Paul Plantinga p.plantinga at ee.wits.ac.za
Thu Jul 24 10:20:20 EDT 2003

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) ? 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
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> > cisco-bba at puck.nether.net
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