The Differentiated Services (DiffServ) protocol identifies two primary types of per-hop behaviors (PHBs), representing two service levels, or forwarding classes. Expedited Forwarding (EF) 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. AF traffic exceeding the profile may be either dropped or demoted during periods of network congestion. See also bandwidth, buffer, congestion, delay, DiffServ, EF, jitter, PHB, and protocol.