[cisco-voip] How to check for QoS?
Wes Sisk
wsisk at cisco.com
Tue Jan 6 15:27:18 EST 2009
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> 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
> <mailto: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>
> <mailto:jvw at medicineforthedefense.com> wrote:
>>
>>
>>
>> Litigation Management
>>
>>
>>
>> Serious Medicine for the Defense ®
>> <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
>> <mailto:jvw at medicineforthedefense.com>
>>
>>
>> PRIVILEGE AND CONFIDENTIALITY NOTICE
>>
>> The information in this electronic mail is intended for the named
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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
>> <mailto: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 <mailto: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>
>> [mailto: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 <mailto:cisco-voip at puck.nether.net>
>> *Subject:* [cisco-voip] How to check for QoS?
>>
>>
>>
>>
>>
>>
>> Litigation Management
>>
>>
>>
>> Serious Medicine for the Defense ®
>> <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
>> <mailto: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
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>>
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>>
>>
>> --
>> Sean Walberg <sean at ertw.com <mailto:sean at ertw.com>>
>> http://ertw.com/
>>
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>
>
>
>
> --
> Sean Walberg <sean at ertw.com <mailto:sean at ertw.com>> http://ertw.com/
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