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New Member

Setting CCM QoS packet marking

By default, when CCM 3.2(2c)SPG is plugged into a switch, no COS appears to be set at layer 2. (not sure about Layer 3 TOS)

Is there something which can be configured on the CCM to set the COS?

or should the switch port do the layer 2 marking?

e.g. classify web traffic to Cos=0, signalling traffic to Cos=3

If TOS is set at L3, should some ACLs and class/policy maps be set up to set COS=TOS?

Is this important anyway? i.e. set the switch to mark all traffic to a COS=3 (assuming COS=3 goes in a high priority queue) and let web+signalling traffic be prioritised through the network?

I have a CCM cluster connected to a 2950 switch which is particularly dumb when it comes to QoS. All it appears possible to do is classify unmarked packets at L2 to a COS=3.

  • Other Collaboration Voice and Video Subjects
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Silver

Re: Setting CCM QoS packet marking

The current release of Cisco CallManager includes the ability to configure the CoS and ToS values for all VoIP control and management traffic from CallManager, the IP phones, H.323, Skinny Protocol, and MGCP gateways. With this user-configurable classification, network element access lists are no longer required to mark VoIP control traffic.

In the callmanager service parameters you 've got :

IpPrecedence : Used by anyone who configures streaming, phones, media applications, etc. Cisco strongly recommends that this parameter never be changed.

IpTosCm2Cm : Controls class of service of IP traffic and signals between Cisco CallManager to Cisco CallManager. Note: The following list shows that the valid value for IpTosCm2Cm is between 0 and 7 and is represented as follows: 0 = routine 1 = priority 2 = immediate 3 = flash 4 = flashOver 5 = critical 6 = internet 7 = network

IpTosCm2Dvce : Controls class of service of IP traffic and signals between Cisco CallManager to device. Controls class of service of IP traffic and signals between Cisco CallManager to Cisco CallManager. Note: The following list shows the valid value for IpTosCm2Dvce is between 0 and 7 and is represented as follows: 0 = routine 1 = priority 2 = immediate 3 = flash 4 = flashOver 5 = critical 6 = internet 7 = network

Regarding 2950 being a dumb one when it comes to QoS, you would probably like to have a look at the following document to see what can be done there

http://www.cisco.com/application/pdf/en/us/guest/netsol/ns17/c649/ccmigration_09186a00800d67ed.pdf

New Member

Re: Setting CCM QoS packet marking

We have been following the QoS SRND and read the paragraph you quote, however, we are unable to spot where CCM sets a COS value. As you point out, you can set the TOS value.

We have IpTosCm2Cm/IpTosCm2Dvce set at 3 and 3 for 'flash' control traffic. We are not running Auto Attendant, so no voice goes to the CCMs. However, without an ACL on the ingress port of the switch which converts the IP TOS to a L2 COS, it is no use setting the TOS. Also:

Q to Cisco: We have 'sniffed' the traffic from the CCM and it does not honour these settings. All traffic from the CCMs has no COS and TOS=0. Do we need to raise a TAC case?

If it did work, the 2950 policy map only allows alteration of DSCP. As you can't set an ACL to match on TOS, you can't convert TOS to DSCP to COS.

So, we could use reams of ACLs to convert to specific UDP/TCP ports to DSCP. And then set specific DSCP to COS mappings. This would enable differentiation of HTTP, etc traffic from Control traffic and set COS to 0 and 3 respectively. But it appears easy to misconfigure and overkill.

Simply setting

mls qos cos 3

mls qos cos override

on the CCM ports on the 2950 is easier but doesn't differentiate between HTTP and control traffic.

Q to Cisco: Can CCMs set the COS value as the Aug 2000 QoS SRND guide suggests or is the guide incorrect?

Q to Cisco: Does it matter if HTTP traffic to/from the CCMs is classified with the same COS=3 setting? Would it affect CCM operation as control packets aren't dropped and only very occaisionally will they have to wait (microseconds) for HTTP (or other non-control) packets to serialise?

Q: Is the 2950 not up to the job and should we go and buy 3550s instead ! :-<

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