[cisco-voip] How to check for QoS?

Tue Jan 6 10:32:33 EST 2009

You probably have your switch set to trust the phone's markings, so it's the
phone setting the DSCP bits.
Having the markings set without a policy doesn't do you any good.  Each
device along the path is just going to treat the packet the same as the
other packets.

Sean

On Tue, Jan 6, 2009 at 9:28 AM, Weigand, John V. <
jvw at medicineforthedefense.com> wrote:

>    [image: Litigation Management]
>
> Serious Medicine for the Defense (R) <http://www.medicineforthedefense.com/>
>
>  Thanks so much for everyone's input, it's very much appreciated!
>
>
>
> "show policy-map" on both our voice and data routers is returning with
> nothing, so I'm taking that to mean we don't have any policies applied on
> those.
>
>
>
> I was able to get the packet capture into Wireshark, and the RTP packets
> are showing the following:
>
>
>
> Differentiated Services Field: 0xb8 (DSCP 0x2e: Expedited Forwarding; ECN:
> 0x00)
>
>                 1011 10.. = Differentiated Services Codepoint: Expedited
> Forward (0x2e)
>
>
>
> Based on my very limited knowledge, that does look like we're applying QoS
> somewhere? If that is the case, would it be applied at the switchports?
>
>
>
>  *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
>
> PRIVILEGE AND CONFIDENTIALITY NOTICE
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> *From:* Sean Walberg [mailto:swalberg at gmail.com]
> *Sent:* Monday, January 05, 2009 5:37 PM
> *To:* James Buchanan
> *Cc:* Weigand, John V.; cisco-voip at puck.nether.net
> *Subject:* Re: [cisco-voip] How to check for QoS?
>
>
>
> 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
>
>
> PRIVILEGE AND CONFIDENTIALITY NOTICE
>
> The information in this electronic mail is intended for the named
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> be protected under law by the Health Insurance Portability and
> Accountability Act. Any use of this information by anyone other than the
> intended receiver is prohibited. If the reader of this message is not the
> intended recipient, you are hereby notified that any dissemination,
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> strictly prohibited. If you have received this message in error, please
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>
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>
>
> --
> Sean Walberg <sean at ertw.com>    http://ertw.com/
>

-- 
Sean Walberg <sean at ertw.com>    http://ertw.com/
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