User manual
Page 27
802.1p
, there is no standard or amendment by that name published by the IEEE. Rather the technique
is incorporated into IEEE 802.1Q standard which specifies the tag inserted into an Ethernet frame.
Priority levels
Eight different classes of service are available as expressed through the 3-bit PCP field in an IEEE
802.1Q header added to the frame. The way traffic is treated when assigned to any particular class is
undefined and left to the implementation. The IEEE however has made some broad recommendations:
PCP Priority Acronym
Traffic Types
1
0 (lowest) BK
Background
0
1
BE
Best Effort
2
2
EE
Excellent Effort
3
3
CA
Critical Applications
4
4
VI
Video, < 100 ms latency and jitter
5
5
VO
Voice, < 10 ms latency and jitter
6
6
IC
Internetwork Control
7
7 (highest) NC
Network Control
6.5.3 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.