- The Per-Hop Behavior (PHB) is indicated by encoding a 6-bit value called the Differentiated Services Code Point (DSCP) into the 8-bit Differentiated Services (DS) field of the IP packet header. - A network could have up to 64 (i.e. 26 ) different traffic classes using different markings in the DSCP. - Most networks use the following Per- Hop Behaviors: 1. Default PHB (same as Best effort traffic). 2. Expedited Forwarding (EF) PHB. 3. Assured Forwarding (AF) PHB. 4. Class selector PHB. (2.4) Expedited Forwarding (EF) PHB:- - The EF PHB has the characteristics of low delay; low loss and low jitter, and is suitable for voice, video and other real-time services. - Typical networks will limit EF traffic to no more than 30%, and often much less of the capacity of a link. (2.5) Assured Forwarding (AF) PHB:- - Assured forwarding allows the operator to provide assurance of delivery as long as the traffic does not exceed some subscribed rate. - Traffic that exceeds the subscription rate faces a higher probability of being dropped if congestion occurs. - The AF behavior group defines four separate AF classes. Within each class, packets are given drop precedence (high, medium or low). - If congestion occurs within a class, the packets with the higher drop precedence are discarded first. - All traffic assigned to a class is initially given low drop precedence