3Com Switch 7750 Configuration Guide Guide

Overview 615
■ 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.
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 157 An Ethernet frame with a 802.1Q tag header
As shown in the figure above, each host supporting 802.1Q protocol adds a 4-bit
802.1Q tag header after the source address of the former Ethernet frame header
when sending packets.
Table 485 Description on DSCP values
DSCP DSCP value (decimal) DSCP value (binary)
ef 46 101110
af11 10 001010
af12 12 001100
af13 14 001110
af21 18 010010
af22 20 010100
af23 22 010110
af31 26 011010
af32 28 011100
af33 30 011110
af41 34 100010
af42 36 100100
af43 38 100110
cs1 8 001000
cs2 16 010000
cs3 24 011000
cs4 32 100000
cs5 40 101000
cs6 48 110000
cs7 56 111000
default (be) 0 000000