Priority Trust Mode - H3C S3100 8C SI Operation Manual

Operation Manual – QoS-QoS Profile
H3C S3100 Series Ethernet Switches

1.3.2 Priority Trust Mode

I. Precedence types
1) IP precedence, ToS precedence, and DSCP precedence
Figure 1-2 DS field and ToS byte
The ToS field in an IP header contains eight bits numbered 0 through 7, among which,
The first three bits indicate IP precedence in the range 0 to 7.
Bit 3 to bit 6 indicate ToS precedence in the range of 0 to 15.
In RFC2474, the ToS field in IP packet header is also known as DS field. The first
six bits (bit 0 through bit 5) of the DS field indicate differentiated service codepoint
(DSCP) in the range of 0 to 63, and the last two bits (bit 6 and bit 7) are reserved.
Table 1-2 Description on IP Precedence
IP Precedence (decimal)
0
1
2
3
4
5
6
7
In a network providing differentiated services, traffics are grouped into the following four
classes, and packets are processed according to their DSCP values.
Expedited Forwarding (EF) class: In this class, packets can be forwarded
regardless of link share of other traffic. The class is suitable for preferential
services with low delay, low packet loss ratio, low jitter, and assured bandwidth
(such as virtual leased line);
IP Precedence (binary)
000
001
010
011
100
101
110
111
1-5
Chapter 1 QoS Configuration
Description
Routine
priority
immediate
flash
flash-override
critical
internet
network