Industrial Ethernet Switch User Manual
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header when using VLAN tagged frames as defined by IEEE 802.1Q. It specifies a
priority value of between 0 and 7 inclusive that can be used by QoS disciplines to
differentiate traffic. Although this technique is commonly referred to as
IEEE 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.
802.1P defined 8 priorities
（
0-7
）
, corresponding 4 priority (High, Medium, Normal,
Low)
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.
6.3 Tos
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)
