3-3
DSCP value (decimal) DSCP value (binary) Description
56 111000 cs7
0 000000 be (default)
2) 802.1p priority
802.1p priority lies in Layer 2 packet headers and is applicable to occasions where the Layer 3 packet
header does not need analysis but QoS must be assured at Layer 2.
Figure 3-2 An Ethernet frame with an 802.1Q tag header
As shown in
Figure 3-2, the 4-byte 802.1Q tag header contains a 2-byte Tag Protocol Identifier (TPID)
whose value is 8100 and a 2-byte Tag Control Information (TCI). TPID is a new class defined by IEEE to
indicate a packet with an 802.1Q tag.
Figure 3-3 describes the detailed contents of an 802.1Q tag
header.
Figure 3-3 802.1Q tag header
In the figure above, the 3-bit priority field in TCI is 802.1p priority in the range of 0 to 7. In the figure
above, the priority field (three bits in length) in TCI is 802.1p priority (also known as CoS precedence),
which ranges from 0 to 7.
Table 3-3 Description on 802.1p priority
802.1p priority (decimal) 802.1p priority (binary) Description
0 000 best-effort
1 001 background
2 010 spare
3 011 excellent-effort
4 100 controlled-load
5 101 video
6 110 voice
7 111 network-management
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