DiffServ is more than I've explained. As the DiffServ bibliography specifies, we differentiate boundary nodes and interior nodes. These are two important points in the traffic path. Both types perform a classification when the packets arrive. Its result may be used in different places along the DS process before the packet is released to the network.
Classifier is invoked.
We will use this value in the future to index a mask- value table. Just change the mask and value of the class you want to remark. First of all, supose we receive a packet marked as EF . If you read RFC2598, you'll see that DSCP recommended value for EF traffic is 101110. The packet arrives, then, set with 0xb8 value at DS field.