Qos on Cisco switch 2960 for IP Phone and Video

[Arbenjamin]

Dear All,

I am a beginner of the Cisco Swtich IPT world, and would like to ask some question in Cisco 2960 switch.

In our lab network, we would like to deploy Cisco IP phone 2960 and Tandberg video conference C40.In order to have better performance, we want to configure the Qos on the switch. However, IP phone frame is using CoS while Video conference use DSCP. So ,the Qos configuration should be base on Cos or DSCP?

By the way, we would like to know any configuration is required between switch and router based on QoS consideration?

Best Regards,

Ben

[Jonathan Schulenberg]

Cisco IP Phones set both CoS and DSCP markings on the packet. The CoS values exist only over the 802.1Q trunk, at which point the switch maps them to the IP layer DSCP markings if you are using trust mls cos. DSCP markings stay with the packet, CoS dies as soon as it exits the 802.1Q trunk. Traditionally the design guidence to trust CoS was an easy way of clearing any DSCP markings from the untrusted data VLAN attached to the phone.

the Qos configuration should be base on Cos or DSCP?

It can be either, just make sure you update the CoS to DSCP mappings as CoS 5 maps to the wrong DSCP value by default.

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

know any configuration is required between switch and router based on QoS consideration?

Typically you trust the upstream port so it would be mls qos trust.

Additional guidence is available in the SRND:

http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book.html

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