107
The DSCP value used to identify 64 levels (2
6
=64) of service determines the forwarding behavior that each
packet gets across the DiffServ network. Based on the marking rule different kinds of traffic can be marked
for different priorities of forwarding. Resources can then be allocated according to the DSCP values and the
configured policies.
The following is an illustration about how the bits are used in DSCP field.
Bit 0
Bit 1
Bit 2
Precedence Usage
1
1
1
7
Stays the same(link layer and routing protocol keep
alive)
1
1
0
6
Stays the same(used for IP routing Protocols)
1
0
1
5
Express Forwarding (EF)
1
0
0
4
Class 4
0
1
1
3
Class 3
0
1
0
2
Class 2
0
0
1
1
Class 1
0
0
0
0
Best effort
Bit 3
Bit 4
Bit 5
Usage
Meaning
0
--
--
Delay
Normal
1
--
--
Delay
Low
--
0
--
Throughput
Normal
--
1
--
Throughput
High
