Like Integrated Services (IntServ), Differentiated Services(DiffServ) is a method for transmitting real-time applications via the Internet or intranets. In DiffServ, the quality of service is subdivided into a few QoS classes, with each service class being provided with a set of rules, the per- hop behavior( PHB).
DiffServ defines different levels of service: expedited forwarding( EF), default forwarding( DF), and assured forwarding( AF). The Differentiated Services is considerably simpler than the Integrated Service because not every data flow has to be managed. Data is only processed at the ingress of the DiffServ network and the classes of service are specified. To do this, the DSCP field in the DiffServ header is marked accordingly. This field corresponds to the Type-of-Service( ToS) field in the IPv4 header or the Traffic Class Octet in IPv6 and is used to keep the individual data flows of a traffic bundle apart.
However, the DSCP field, Differential Service Code Point, is 6 bits long and therefore can represent 64 classes. If multiple Internet Service Providers(ISPs) are involved in a DiffServ connection, then the class of service is negotiated between each ISP for each new ISP network. The service class agreements are defined in the Service Level Specifications( SLS).
DiffServ is specified in RFC 1349.