3com 4210 PWR 9-Port 3CR17341-91-ME User Manual
Product codes
3CR17341-91-ME
302
C
HAPTER
28: Q
O
S C
ONFIGURATION
■
Class selector (CS) class: This class comes from the IP ToS field and includes
eight subclasses;
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.
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.
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.
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
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.
4-byte 802.1Q tag header after the source address of the former Ethernet frame
header when sending packets.
Table 221 Description of 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)
Length/Type
Data
6 bytes
6 bytes
4 bytes
2 bytes
46~1517 bytes
4 bytes
TPID
TCI
Source
Address
Destination
Address
802.1Q
header
FCS
(CRC-32)