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. (Internal priorities are also called local priorities, and are used to differentiate classes of service for packets.) After priority mapping, the switch provides differentiated services for packets based on the internal priorities.

Packets transmitted over different networks carry different QoS precedence fields. For example, the EXP field is used on a Multiprotocol Label Switching (MPLS) network, the 802.1p field is used on a virtual local area network (VLAN), and the DSCP field is used on an IP network. To retain the priorities of packets that traverse different networks, priority mapping must be configured on network devices. When the switch connects different types of networks, it maps external precedence fields (including 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.