[cisco-voip] How to check for QoS?

[James Buchanan]

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?

 

	 Litigation Management<http://www.medicineforthedefense.com/main/gifs/LMI-side-pms690wBlack.jpg> 

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 

	


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