qos video conference within LAN

Answered Question
Nov 9th, 2009

Hi All, newbie to qos.

Trying to get qos implemented within our district bw two video conf units.

I've attached a sketch of what I've done and what I'm planning to do.

Hoping for some best practice advice, or corrections on what I might have done wrong.

Polycom

Set to Diffserv with values of 34(aka af41 I believe) for both audio and video

3750

mls qos globally

polycom switchport: mls qos trust dscp, (do I need auto qos voip trust or cisco-phone?)

switchport uplink: mls qos trust dscp (or is this cos)

3750

mls qos globally

switchport downlink: mls qos trust dscp (or cos)

Layer 3 port: mls qos trust dscp (or cos)

do I need auto qos enabled on any of these ports?

6509

mls qos globally

Layer 3 port: mls qos trust dscp (or cos)

do I need auto qos enabled on any of these ports?

Just curious are there any special show cmds for qos? To show that it's actually working or making a difference?

Let me know if additional info is needed, thanks in advance, RT

I have this problem too.
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Correct Answer by Edison Ortiz about 7 years 1 month ago

Hi Roger,

In addition to trusting the switchports, I also suggest changing the default cos-dscp mappings on every single switch.

The command is: mls qos map cos-dscp 0 8 16 26 32 46 48 56

Auto-QoS will provide a baseline to work from but based on your requirements, it is sufficient with just MLS QOS turned on globally and trust dscp on the interested switchports (polycom + inter-switch links).

As for OAM, you will need to consult the documentation for each switch as the commands differ.

On the 3750s, you can use the show mls qos interface stat command to view input and output markings while in the 6500, you may need to enable NetFlow to view QoS information on the packet.

You can find also a lot of information on the QoS SRND.

http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoSDesign.html

Regards

Edison.

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Correct Answer
Edison Ortiz Mon, 11/09/2009 - 13:02

Hi Roger,

In addition to trusting the switchports, I also suggest changing the default cos-dscp mappings on every single switch.

The command is: mls qos map cos-dscp 0 8 16 26 32 46 48 56

Auto-QoS will provide a baseline to work from but based on your requirements, it is sufficient with just MLS QOS turned on globally and trust dscp on the interested switchports (polycom + inter-switch links).

As for OAM, you will need to consult the documentation for each switch as the commands differ.

On the 3750s, you can use the show mls qos interface stat command to view input and output markings while in the 6500, you may need to enable NetFlow to view QoS information on the packet.

You can find also a lot of information on the QoS SRND.

http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoSDesign.html

Regards

Edison.

rhopkins_rcps Tue, 11/10/2009 - 05:39

Hey Edison, thanks for the quick response.

So you're saying the only cmds that are of interest in my situation would be:

mls qos (globally)

mls qos map cos-dscp 0 8 16 26 32 46 48 56 (globablly)

mls qos trust dscp (for L2 and L3 interfaces, does it make a difference if they're trunk ports?)

I don't have to worry with setting up the various queues, right?

Just to educate myself here, when would I use "mls qos trust cos"?

Thanks for the link, I'll be reading through it.

Thanks for the help, RT

Edison Ortiz Tue, 11/10/2009 - 06:50

The 3 commands listed above will cover your requirements for QoS trust and correct internal ToS map.

Trusting Class of Service usually takes place on trunk links as this type of trust will inspect the 802.1q header. However, if you configure DSCP trusting, the value will be read as COS then translated to DSCP - that's the reason I suggested to modify the default maps for proper queue allocation.

The link I provided explains all these nuisances, take a moment and read them carefully.

Regards

Edison.

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