[cisco-voip] How to check for QoS?

Tue Jan 6 15:59:09 EST 2009

It's not a simple thing to prove as you point out, but it's simple to
disprove.

He's got no policy-map on the router and has shown that DSCP tags are not
being carried over the WAN for a voice call.

I'm sure all of us who are router jocks could pull out our DocCDs and come
up with some configs that would technically give voice protection against
jitter and starvation, and also guarantee signaling gets through in times of
congestion, and still not use DSCP/IPP tags or MQC.  But even if we could,
would you recommend using it?

But, playing the odds, something's not right with his QoS config, whatever
it is.  The question wasn't a laundry list of all the possible options
(which is good to have if one wants to plan this), but it was from a
business person to a techie, "Is QoS configured?"

When I heard the question, I took off my techie beanie and put on my
business hat.  "Does my network provide what voice needs to get through and
ensure quality and reliability?".

Again, playing the odds, I'm going to answer "No".  I don't have to worry
about border elements, which tags he's using for what, or what kind of
hardware queues he's running.  I'm not designing his network, I'm trying to
help him answer a simple question.  Somewhere the DSCP tags are getting
stripped. In my books, QoS isn't configured correctly, it needs to be looked
at.

The followup questions to this, though, are not simple, and your questions
would be a good start. :)

Sean

On Tue, Jan 6, 2009 at 2:27 PM, Wes Sisk <wsisk at cisco.com> wrote:

>  what does 'if QoS was enabled' mean?
> cisco hardphones: set DSCP according to CM config barring a few defects
> cm: QoS is configurable depending on customer policy
> voice gateways: QoS configurable depending on customer policy
> what method of CAC is in use? GK, CM Locations, RSVP?
> switches: may or may not trust phones, but are you doing dot1q or dot1p
> tagging to take advantage of L2 QoS?  Are you trusting phone QoS?
> network: do the devices even support any type of QoS? 1q2T 2q2T.... are
> their priority output queues? is it such high bandwith with such low
> utilization that QoS is N/A?  are firewalls, Border Elements, or Proxies in
> use?  Do those preserve ip prec or DSCP?
> what is the standard for QoS in the network? ip prec or DSCP?  what QoS
> classes are in use on the network?  there are recommended defaults but those
> do not have to be followed.
> are there soft clients in use?  how is QoS designed and deployed for those?
>
> The net is that QoS is 7 parts technical and 3 parts policy.
>
> Proper QoS depends on agreement between the policy and the configuration of
> devices.
>
> the simple question unfortunately is not so simple.
>
> /wes
>
>
> On Tuesday, January 06, 2009 3:12:51 PM, Sean Walberg <swalberg at gmail.com><swalberg at gmail.com>wrote:
>
> To be fair, he only asked how he could find out if QoS was enabled or not.
>  It pretty clearly is not, so he might be able to pass the buck off to
> someone else :)
>  Sean
>
> On Tue, Jan 6, 2009 at 2:05 PM, Wes Sisk <wsisk at cisco.com> wrote:
>
>>  Hi John,
>>
>> There are many facets to QoS.  I recommend you grab a six pack of
>> caffeine, a quiet room, and the QoS SRND.
>>
>> Regards,
>> Wes
>>
>> On Tuesday, January 06, 2009 10:28:37 AM, Weigand, John V.
>> <jvw at medicineforthedefense.com> <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
>>
>> The information in this electronic mail is intended for the named
>> recipients only. It may contain privileged and confidential material and may
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>>
>>  *From:* Sean Walberg [mailto:swalberg at gmail.com <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
>> recipients only. It may contain privileged and confidential material and may
>> 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,
>> distribution, copying, or other use of this message or its attachments is
>> strictly prohibited. If you have received this message in error, please
>> notify the sender immediately by replying to this electronic e-mail or by
>> calling (800) 778-5424. Please delete it from your computer. Thank you.
>>
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>>
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>>
>>
>>
>> --
>> Sean Walberg <sean at ertw.com>    http://ertw.com/
>>
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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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