PHB - technical definition

In the Differentiated Services (DiffServ) protocol, a service level, or forwarding classes. Expedited Forwarding (EF), for example, provides minimal delay, jitter, and loss. Assured Forwarding (AF) comprises four classes, each of which contains three drop precedences and allocates certain amounts of buffer space and bandwidth. DiffServ operates on a packet-by-packet and hop-by-hop basis. See also AF, bandwidth, buffer, delay, DiffServ, EF, hop, jitter, packet, and protocol.