248
Appendix Packet precedences
IP precedence and DSCP values
Figure 249 DS field and ToS field
As shown in Figure 249, the ToS field of the IP header contains 8 bits: the first 3 bits (0 to 2) represent IP
precedence from 0 to 7. According to RFC 2474, the ToS field of the IP header is redefined as the
differentiated services (DS) field, where a differentiated service code point (DSCP) value is represented
by the first 6 bits (0 to 5) and is in the range 0 to 63. The remaining 2 bits (6 and 7) are reserved.
Table 119 Description on IP precedence
IP
recedence (decimal) IP
recedence (binar
)
Ke
word
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 120 Description on DSCP values
DSCP value (decimal) DSCP value (binar
)
Ke
word
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