CoS on inbound call

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Jan 25th, 2010
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I used Wireshark recently to verify the CoS markings on Cisco IP phones during calls.  The frames on packets travelling between phones shows CoS 5 on call traffic and CoS 3 on control traffic.  When a call is received from an outside DID, the IP conversation is between a Phone and the Call Manager.  In that case I still see the CoS 5 & 3 Markings on packets coming from the phone.  However, the packets coming from the CM appear to have CoS 0 for all traffic.  Shouldn't the CoS on traffic coming from the CM be marked with CoS 5 & 3 as well?  Is that a configurable on the CM?


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Jonathan Schulenberg Mon, 01/25/2010 - 20:53
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First, only signaling (SCCP or SIP traffic) will be coming from UCM. The RTP traffic will be coming from a router most likely. You should be clear what traffic is coming from where.

In both cases what are the switchport configurations of the switch those devices are plugged into? Catalyst switches clear DSCP markings (COS only exists across 802.1q trunks) on switchports that are not trusted.

Enterprise  QoS Solution Reference Network Design Guide Version 3.3


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