[cisco-voip] How to check for QoS?

Tue Jan 6 17:18:38 EST 2009

http://www.medicineforthedefense.com/
I just want to thank everyone for the responses - a lot of information
to digest, but it has been extremely helpful!

With all the suggestions and some other things I was able to find, we've
certainly been able to prove at the very least that things are not quite
as they should be, which we suspected, and that was all that we need for
now. 

Luckily, we're getting ready to pretty much overhaul everything as part
of a building move, and bring in some people who actually know what
they're doing, so I think we'll be able to get it all straightened out.

Thanks again!

From: Sean Walberg [mailto:swalberg at gmail.com] 
Sent: Tuesday, January 06, 2009 3:59 PM
To: Wes Sisk
Cc: Weigand, John V.; James Buchanan; cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] How to check for QoS?

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> <mailto: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> <mailto:jvw at medicineforthedefense.com>
wrote:

	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 

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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?

	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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may be protected under law by the Health Insurance Portability and
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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: 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 computer. Thank you.

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

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