3Com 4210 PWR Configuration Manual page 304

302 C 28: Q S C
HAPTER O ONFIGURATION
Class selector (CS) class: This class comes from the IP ToS field and includes
■
eight subclasses;
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 221 Description of DSCP precedence values
DSCP value (decimal)
46
10
12
14
18
20
22
26
28
30
34
36
38
8
16
24
32
40
48
56
0
802.1p 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 93 An Ethernet frame with an 802.1Q tag header
Source
Destination
Address
Address
6 bytes 6 bytes
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.
DSCP value (binary)
101110
001010
001100
001110
010010
010100
010110
011010
011100
011110
100010
100100
100110
001000
010000
011000
100000
101000
110000
111000
000000
802.1Q
header
Length/Type
TPID TCI
4 bytes 2 bytes
Description
ef
af11
af12
af13
af21
af22
af23
af31
af32
af33
af41
af42
af43
cs1
cs2
cs3
cs4
cs5
cs6
cs7
be (default)
FCS
Data
(CRC-32)
46~1517 bytes 4 bytes