Priority mapping

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Packets transmitted over different networks carry different QoS precedence fields, for example, EXP field on an MPLS network, 802.1p field on a virtual local area network (VLAN), and DSCP field on an IP network. The mapping between priority fields must be configured on the gateway to retain priorities of packets when the packets traverse different networks.
The priority mapping mechanism provides the mapping from precedence fields of packets to internal priorities (local precedences) or the mapping from internal priorities to precedence fields of packets. This mechanism uses the DiffServ domain to manage and record the mapping of precedence fields and internal priorities. When packets reach the AR, the AR maps priorities in packets or the default 802.1p priorities of inbound interfaces to local priorities. The AR then determines the queues that packets enter based on the mapping between internal priorities and queues and performs traffic shaping, congestion avoidance, and queue scheduling. In addition, the AR can re-mark priorities in outgoing packets so that the downstream device can provide different QoS levels based on packet priorities.

Other related questions:
Default mappings between priorities on an AR
Default mappings between priorities on an AR are as follows: For the AR120&AR150&AR160&AR200&AR500 series, AR510 series, AR1200 series, AR2204, AR2220L, and AR2220E, table 1 shows the mappings from 802.1p priorities to DSCP priorities, and the mappings between 802.1p priorities remain unchanged. Table 3 lists the mappings from DSCP priorities to 802.1p priorities, and the mappings between DSCP priorities remain unchanged. The mappings between MPLS EXP priorities remain unchanged. For AR2201-48FE, AR2202-48FE, AR2220, AR2240, and AR3200&AR3600 series, table 2 lists the mappings from 802.1p priorities to DSCP priorities and local priorities, and the mappings between 802.1p priorities remain unchanged. Table 4 lists the mappings from DSCP priorities to 802.1p priorities and local priorities, and the mappings between DSCP priorities remain unchanged. Table 5 lists the mappings from MPLS EXP priorities to local priorities, and the mappings between MPLS EXP priorities remain unchanged.

How to configure mapping between DSCP priorities and local priorities on S series switches
You can run the following commands to configure mapping between DSCP priorities and local priorities on S series switches (except the S1700): - ip-dscp-inbound dscp-value phb service-class [ green | yellow | red ]: configures mapping between DSCP priorities and local priorities for IP packets on the inbound interface. - ip-dscp-outbound service-class { green | yellow | red } map dscp-value: configures between DSCP priorities and local priorities for IP packets on the outbound interface.

How to configure priority mappings on an AR
You can configure priority mappings on an AR as follows: 1. Configure the packet priority trusted on an interface. 2. (Optional) Configure the interface priority. 3. Configure a priority mapping table.

What are the mappings between WMM queues and 802.1p priorities
WMM classifies data packets into four queues. 802.1P provides eight priorities. Users can configure the mappings between WMM queues and 802.1p priorities.

Mapping between differentiated services code point (DSCP) and local priority
IP packets carry the DSCP field to indicate the QoS preference. The mapping between the priority fields must be configured on the gateway to retain packet priorities when the packets traverse different networks. You can run the display qos map-table command to view the mapping between priorities, or run the input command in the priority mapping table view to configure the mapping between priorities.

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