3Com 7757 Configuration Manual page 659

service level can be segmented. The QoS rank of the AF class is lower than that
of the EF class;
Class selector (CS) class: This class comes from the IP TOS field and includes 8
■
classes;
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 529 Description on DSCP values
DSCP
ef
af11
af12
af13
af21
af22
af23
af31
af32
af33
af41
af42
af43
cs1
cs2
cs3
cs4
cs5
cs6
cs7
default (be)
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 in
Layer 2.
Figure 171 An Ethernet frame with a 802.1Q tag header
Source
Destination
Address
Address
6 bytes 6 bytes
DSCP value (decimal)
46
10
12
14
18
20
22
26
28
30
34
36
38
8
16
24
32
40
48
56
0
802.1Q
header
Length/Type
TPID TCI
4 bytes 2 bytes
Overview 659
DSCP value (binary)
101110
001010
001100
001110
010010
010100
010110
011010
011100
011110
100010
100100
100110
001000
010000
011000
100000
101000
110000
111000
000000
FCS
Data
(CRC-32)
46 to 1500 bytes 4 bytes