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What is the default QoS behaviour of the 6608 PRI and 6624 FXS Catalyst 6000 cards?
The 6608 and 6624 cards are not configurable for Quality of Service (QoS). Therefore, you need to understand the default tagging behaviour of these cards and, if necessary, take action on the Catalyst switch to conform to the QoS policy being implemented network wide.
The 6608 and 6624 internal port is treated as trust-cos to the Catalyst 6000. So the default COS-to-DSCP mapping of the cards will determine the DSCP values with which the IP packets are marked unless they are changed in the switch.
The 6608 and 6624 will tag packets as follows:
COS = 5 for rtp traffic
COS = 3 for signalling traffic
By default on the Catalyst 6000, these COS values map in IP packets to DSCP 24 (COS = 3) and 40 (COS = 5) as shown in the table below.
Generally, the recommended DSCP values to use in a VoIP network differ slightly. They are:
It may be necessary to change the default COS-DSCP mapping on the Catalyst 6000 so that the DSCP markings in packets generated by the 6608 and 6624 cards conform to the network policy. For example, if other devices in the network are marking packets with the recommended values.