Overview of Priority Mapping

Priority mapping is a method of translating Quality of Service (QoS) precedence fields carried in packets into internal priorities on a device. These internal priorities, also called local priorities, are used to differentiate classes of service for packets. After priority mapping is configured, the device provides differentiated services for packets based on the internal priorities.

Packets transmitted over different networks carry different QoS precedence fields. For example, an 802.1p field is used on a virtual local area network (VLAN), an EXP field is used on an MPLS network, and a DSCP field is used on an IP network. If packets traverse different types of networks, priority mapping must be configured on network devices to retain priorities of packets. A device that connects different types of networks maps the external precedence fields (such as 802.1p, MPLS EXP, and DSCP) of all the received packets to internal priorities. When the device sends packets, it maps internal priorities to external priorities.