[cisco-voip] How to check for QoS?

[Wes Sisk]

fully agreed with everything stated here.  in addition ttcp can be a  
useful tool for generating traffic to verify QoS functionality and  
performance.  When all implemented properly you should be able to slam  
links with traffic and maintain signaling (no or nominal delay offhook  
to dialtone) and media (good voice quality with no or nominal packet  
jitter and loss)

regards,
wes

On Jan 5, 2009, at 5:36 PM, Sean Walberg wrote:

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?




Serious Medicine for the Defense ®

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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