per-hop behavior (QoS) (PHB)
In Differentiated Services( DiffServ) and in Multi-Protocol Label Switching( MPLS), the user can request a specific transmission quality for the data packets.
This quality request, which is identified by a Differential Service Code Point( DSCP) marker, is called Per-Hop Behavior (PHB). PHB generally describes the allocation of specific bandwidth and storage resources as well as requested traffic characteristics such as delay time or packet loss, allowing differentiation into different classes of service. The PHBs are specified in the IP headers. The different PHB classes include default PHB for best- effort( BE), expedited forwarding for high- priority real-time traffic, and assured forwarding.