1-5
z
Best Effort (BE) class: This class is a special class without any assurance in the CS class. The AF
class can be degraded to the BE class if it exceeds the limit. Current IP network traffic belongs to
this class by default.
Table 1-3
Description on DSCP precedence values
DSCP value (decimal)
DSCP value (binary)
Description
46 101110
ef
10 001010
af11
12 001100
af12
14 001110
af13
18 010010
af21
20 010100
af22
22 010110
af23
26 011010
af31
28 011100
af32
30 011110
af33
34 100010
af41
36 100100
af42
38 100110
af43
8 001000
cs1
16 010000
cs2
24 011000
cs3
32 100000
cs4
40 101000
cs5
48 110000
cs6
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 1-3
An Ethernet frame with an 802.1Q tag header
As shown in the figure above, each host supporting 802.1Q protocol adds a 4-byte 802.1Q tag header
after the source address of the former Ethernet frame header when sending packets.