[cisco-voip] How to check for QoS?

[Sean Walberg]

If you get the packet capture into Wireshark, you can (in addition to
checking for the DSCP == EF) measure the latency to see if QoS is doing its
job.

>From a router, though, you can check your policy maps with "show policy-map"
or "show policy-map interface", it will tell you if a policy is applied and
what it's doing.  You're looking for a priority queue.

The Cisco QoS SRND is a good way to understand QoS.  It's hefty, but most of
the details are duplicated for every model of switch.

Sean

On Mon, Jan 5, 2009 at 4:07 PM, James Buchanan <jbuchanan at ctiusa.com> wrote:

>  Hi John,
>
>
>
> The biggest thing you are looking for is that the voice traffic is being
> marked and that the marking is being recognized throughout the network.  A
> packet capture is the quickest way to determine this. In the packet capture,
> you will see a field for Differentiated Services. For traffic that is the
> actual audio payload, you should see the Differentiated Services field as
> Expedited Forwarding. You will want to check packets going in each
> direction.
>
>
>
> On the switches, for ports that have a phone plugged in you should see that
> the switchport is configured to trust cos and is configured to trust based
> on the device being a cisco phone (mls qos trust cos and mls qos trust
> cisco-phone). What these commands look like can vary according to the model
> of switch.
>
>
>
> For any connection that is a voice server or voice gateway, the switchport
> should trust the dscp value (mls qos trust dscp). This should also be true
> on uplinks from switch to switch and from switch to WAN router.
>
>
>
> On the WAN router, depending upon the speed of your connection you should
> be using some sort of low latency queuing and/or traffic shaping.
>
>
>
> Thanks,
>
>
>
> James
>
>
>
> *From:* cisco-voip-bounces at puck.nether.net [mailto:
> cisco-voip-bounces at puck.nether.net] *On Behalf Of *Weigand, John V.
> *Sent:* Monday, January 05, 2009 4:02 PM
> *To:* cisco-voip at puck.nether.net
> *Subject:* [cisco-voip] How to check for QoS?
>
>
>
> [image: Litigation Management]
>
> Serious Medicine for the Defense (R) <http://www.medicineforthedefense.com/>
>
> I've been tasked with checking to see if our VAR ever setup any QoS at all,
> and if so, what type and how it's set. Unfortunately, although I've become
> fairly proficient at CallManager itself, I'm pretty new to the inner
> workings of everything at the actual network level.
>
>
>
> I know there's a few different ways to set it all up, and I've tried poking
> around, but I'm not really even sure where to begin looking. Does anyone
> have any pointers as to how I might be able to track down some of this info?
> Is there anything I can tell from a packet capture of a call from between
> two of our sites? I do also have read only access to the switches/routers on
> the network.
>
>
>
> Thanks in advance!
>
>
>
> *John V. Weigand*
> Help Desk Support/Executive Support
>
> Litigation Management, Inc.
> 300 Allen-Bradley Drive
> Suite 200
> Mayfield Heights, OH 44124
>
>
>
>
> Tel: 440-484-2000
> Fax: 440-484-2009
> Cell:
> email: jvw at medicineforthedefense.com
>
>
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-- 
Sean Walberg <sean at ertw.com>    http://ertw.com/
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