Manual

138

XMS-1024P

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LUX-UG-XMS-1024P Vers: 081314

Priority Mode

This Switch implements three Priority Modes based on Port, 802.1P and DSCP. By

default, the priority mode based on Port is enabled.

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Port Priority

Port Priority is a property of the Port. After Port Priority is conﬁ gured, the Data stream

will be mapped to the Egress Queues according to the CoS (Cost of Service) of the Port

and the Mapping relationship between CoS and Queues.

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802.1P Priority

Figure 9-2 802.1Q frame

As shown in the ﬁ gure above, each 802.1Q Tag has a PRI ﬁ eld, comprising 3 bits. The

3-bit priority ﬁ eld is 802.1P Priority with a range of 0-7. 802.1P Priority determines the

priority of the packets based on the PRI value. In the Switch, you can conﬁ gure differ-

ent priority tags mapping to the corresponding priority levels. The Switch determines

which packets are sent with what Priority when forwarding packets. The Switch

processes untagged packets and Maps them to the default priority mode.

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DSCP Priority

Figure 9-3 IP Datagram

As shown in the ﬁ gure above, the ToS (Type of Service) in an IP header contains 8 bits.

The ﬁ rst three bits indicate IP Precedence with a range of 0-7. RFC2474 re-deﬁ nes the

ToS ﬁ eld in the IP packet header which is called the DS ﬁ eld. The ﬁ rst six bits (bit 0-5)

of the DS ﬁ eld indicate DSCP precedence with a range of 0-63. The last 2 bits (bit 6

and bit 7) are reserved. In the Switch, you can conﬁ gure different DS Field Mappings to