DiffServ with IP Packets

Refer to Figure 12-1 to refresh your memory about what the IP header looks like.

Figure 12-1. IP Header Fields

Figure 12-2 shows you how the TOS field is divided.

Figure 12-2. The TOS Byte of the IP Header Defining the Precedence Bits

The usage of the precedence bits for QoS is now widely used throughout the world for many networks. The drawback of the precedence bits, however, is that only three exist, which means you can have only eight levels of service. Therefore, the IETF decided to dedicate more bits for QoS. ...

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