Resolution
Prior to Cisco CallManager 4.0, voice control traffic defaulted to a Differentiated Services Code Point (DSCP) value of 26 / AF31. Cisco CallManager 4.0 and later changes this so that voice control traffic is marked with DSCP 24 /CS3 by default. This change reflects the fact that voice control traffic ideally never drops whereas DSCP AF31 traffic can possibly be dropped in certain instances. Certain voice products still mark voice control traffic as DSCP 26/AF31 although a marking migration to this new marking scheme for Cisco products is planned. It is recommended that both DSCP 26/AF31 and DSCP 24/CS3 markings be reserved for voice control signaling at current Cisco IOS MQC setup.
Refer to Quality of Service on Cisco CallManager for more information.