Re: OT - 3560 srr-queue parameters to prioritise VoIP

Gary,

QoS functionality for the "cheap" Catalyst switches is quite limited.
The 3560 does not support any egress QoS features with except to SRR
queueing. However, this one is powerful enough to provide port and
queue-level shaping. And of course it supports priority queueing, with
one small drawback - there is no easy way to control the priority
queue rate in egress direction. You may apply ingress policing (per
port or per VLAN), which is effectively admission control tool, but
the 3560s do not support aggregate policing over multiple physical
ports.

You may find some basic 3560 SRR configuration examples in my old blog post:

http://blog.ine.com/2008/06/26/quick-notes-on-the-3560-egress-queuing/

which illustrates how SRR weights could be used for shaping and
sharing on individual queues. Unfortunately, there are just four
queues supported, and thus you selection of traffic classes could be
limited. Then, again, 3560s was only positioned as an access-layer
switch.

In your case, you may want to shape the port to 6Mbps and enable the
egress priority queue. The simplest option to classify VoIP traffic is
based on DSCP marking, by trusting the ingress ports. Keep in mind
that the priority queue can make other queues starve, unless you
enforce strict ingress admission control.

HTH

-- 
Petr Lapukhov, petr_at_INE.com
CCIE #16379 (R&S/Security/SP/Voice)
Internetwork Expert, Inc.
http://www.INE.com
Toll Free: 877-224-8987
Outside US: 775-826-4344
2010/4/25 Gary Duncanson <garyduncanson_at_btinternet.com>:
> Hi,
>
> Im researching the following requirement - To prioritise 4M of VoIP traffic on
> a 6M line.
>
> I have a 3550 at one side and a 3560 at the other. It seems to me I can use
> AutoQoS on the 3550 and a service-policy output.
>
> On the 3560 things seem less straightforward as it's the srr-queue stuff at my
> disposal (no service-policy output supported on egress).
>
> Im struggling with best i.e simplest approach to classify traffic on the 3560
> and configure the egress queues to accomplish the 4M priority I need. Has
> anyone any example configs to achieve this?
>
> Thanks
> Gary
>
>
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