HP FlexNetwork NJ5000, Руководство пользователя

Страница: 413 / 475

401
downstream network can either use the classification results from its upstream network or classify
the packets again according to its own criteria.
To provide differentiated services, traffic classes must be associated with certain traffic control
actions or resource allocation actions. What traffic control actions to use depends on the current
phase and the resources of the network. For example, CAR polices packets when they enter the
network. GTS is performed on packets when they flow out of the node. Queue scheduling is
performed when congestion happens. Congestion avoidance measures are taken when the
congestion deteriorates.
Packet precedences
IP precedence and DSCP values
Figure 438 ToS field and DS field
As shown in Figure 438 , the ToS field of the IP header contains 8 bits. According to RFC 2474, the
ToS field of the IP header is redefined as the differentiated services (DS) field, where a differentiated
services code point (DSCP) value is represented by the first 6 bits (0 to 5) and is in the range of 0 to
63. The remaining 2 bits (6 and 7) are reserved.
Table 141 Description on IP Precedence
IP Precedence (decimal) IP Precedence (binary) Description
0 000 Routine
1 001 priority
2 010 immediate
3 011 flash
4 100 flash-override
5 101 critical
6 110 internet
7 111 network
Table 142 Description on DSCP values
DSCP value (decimal) DSCP value (binary) Description
46 101110 ef
10 001010 af11
12 001100 af12
14 001110 af13
0 7 6
DSCP
Class Selector
codepoints
Differentiated Services
Codepoint (DSCP)
RFC 2474
Currently
Unused
DS-Field
(for IPv4,ToS
octet,and for
IPv6,Traffic
Class octet )
1 5 4 3 2 Bits:
CU