Traffic; Traffic Classification; Precedence - H3C S7500 Series Operation Manual

Operation Manual – QoS
H3C S7500 Series Ethernet Switches

1.1.1 Traffic

Traffic means service traffic, that is, all the packets passing the switch.

1.1.2 Traffic Classification

Traffic classification means to identify packets conforming to certain characters
according to certain rules.
A classification rule is a filter rule configured to meet your management requirements. It
can be very simple. For example, you can use a classification rule to identify traffic with
different priorities according to the ToS field in the IP packet header. It can be very
complicated too. For example, you can use a classification rule to identify the packets
according to the combination of link layer (Layer 2), network layer (Layer 3) and
transport layer (Layer 4) information including MAC addresses, IP protocols, source
addresses, destination addresses, the port numbers of applications and so on.
Classification is generally based on the information in the packet header and rarely
based on the packet content.

1.1.3 Precedence

1) IP precedence, ToS precedence and DSCP precedence
DS-Field
(for IPv4,ToS
octet,and for
IPv6,Traffic
Class octet )
Figure 1-1 DS fields and TOS byte
The ToS field in an IP header contains 8 bits:
The high-order 3 bits represent IP precedence in the range of 0 to 7.
Bit 3 to bit 6 represent ToS precedence in the range of 0 to 15.
RFC2474 re-defines the ToS field in the IP packet header, which is called the DS
field. The high-order 6 (bit 0 to bit 5) bits of the DS field represent DSCP
precedence in the range of 0 to 63.The high-order 3 bits in DSCP precedence are
class selector codepoints, bit 4 and bit 5 represent drop precedence, and bit 6
being zero indicates that the device sets the service class by using the DS model.
The lower-order 2 bits (bit 6 and bit 7) are reserved bits.
Bits: 0 1 2 3 4 5
DSCP
Class Selector
codepoints
Differentiated Services
Codepoint (DSCP)
RFC 2474
6 7
IPv4 ToS
CU
byte
Currently
Unused
s
1-2
Chapter 1 QoS Configuration
Bits: 0 1 2 3 4 5
Preced Type of
ence Service
RFC 1349
RFC 1122
IP Type of Service (ToS)
RF C 791
6 7
M
B
Z
Must
Be
Zero