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（
Figure 6.5.3
）
Default priority mark 0 and 1 is low queue, 2 and 3 is normal queue, 4 and 5 is Medium, 6 and 7 is
High.
6.5.4 ToS/DSCP
DiffServ architecture provides each transport packets in the network are classified into different
categories, classified information is contained in the IP packet header, DiffServ architecture using the first
6 bits of IP packet header TOS( Type of Service) to carry the packets' classified information. This
definition is only for the lower 6 bits, one number does not exceed 63. This definition supports both IPv4
(ToS field) and IPv6 (Traffic Class field). DSCP has 64 priority values (0-63), the lowest priority 0 and the
highest priority 63. In fact, the DSCP field is a superset of the IP precedence field, DSCP field definition is
backward-compatible with IP precedence field.
So far, the defined DSCP with default DSCP, the value is 0; class selector DSCP defined as the
backward-compatible with IP precedence, the value(8,16,24,32,40,48,56); Expedited Forwarding (EF),
generally used for low latency service, the recommended value is 46 (101110); identified by forwarding
(AF) defines four service levels, each service level has 3 down process, so spent 12 DSCP values
((10,12,14), (18,20,22), (26,28,30), (34,36,38)).
The priority value of the device (1-16) is defined as the lowest priority, as the first queue. Priority
value (17-32) is defined as the second queue, the priority value (33-48) is defined as the third queue, the
priority value (49-64) is defined as the fastest queue, the highest priority.
