DiffServ

Differentiated Services (DiffServ) is an Internet Engineering Task Force (IETF) method, defined in RFC 2475, for adding a QoS aspect to IP networks. DiffServ works only at Layer 3 (Network layer) of the OSI Reference Model, using per-hop behavior (PHB). The PHB is specified in the DiffServ code point (DSCP), found in the IP type of service (TOS) field in the IPv4 header as the DiffServ byte (DS byte), and the Traffic Class byte in the IPv6 header.

NOTE

It is expected that network service providers will use MPLS within the network backbone and use DiffServ at the network edge for QoS classification and path assignment.

DiffServ is a best-effort service and is currently supported only in IP networks. Where traditional IP networks can be likened to bulk mail in the post office no single item is given preferential treatment or handling over another DiffServ provides for classification of the traffic, similar to First Class mail, Express Mail, and so forth.

DiffServ provides QoS guarantees for aggregates of traffic. Traffic aggregates are made up of a set of packets with the same DSCP, going in the same direction over a given link. DiffServ traffic is separated into classes characterizing their QoS needs; for example, one class is "real-time traffic" and another class is "loss or delay sensitive traffic."