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Ethernet standard by four bytes which was published as IEEE 802.3ac in 1998.
The QoS technique developed by the working group, also known as class of service (CoS),
is a 3-bit field called the Priority Code Point (PCP) within an Ethernet frame 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.
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