Differentiated services in the Internet

Architectures for Internet quality of service (QoS) have been under discussion for over a decade and, with the commercialization of the Internet, the topic has become increasingly important. This paper gives a background and history of QoS for the Internet, then introduces and motivates the differentiated services (Diffserv) approach. The major advantages of the Diffserv approach are that it is a good match to the Internet architecture and that it can be initially deployed with a minimalist approach, adding complexity as needed. Despite the long history of discussion, the phrase "quality of service" does not have a universally accepted meaning. In this paper QoS is used to describe a set of measurable parameters, such as delay, throughput, and loss rate, that can be attached to some identifiable subset of the traffic of IP packets through a given network domain. The identifiable subset of traffic belongs to a "user" of IP QoS where "user" spans a range of granularities, from a single application program to an entire company. Providing guarantees about the values of network parameters requires the implementation and deployment of physical mechanisms throughout the network and then configuring these mechanisms in such a way that their effect, when viewed from the edges of the network, composes into the desired QoS. Diffserv uses simple mechanisms in a more complex composition, allowing the details of the composition to evolve while the mechanisms, part of the network infrastructure, can remain the same. The paper discusses the specifics of this approach and why it is well-matched to the Internet. Some practical issues for deployment are addressed. Further we address resource allocation and configuration questions, including simple possibilities for early deployment and some of the open questions for a more complex future deployment. This paper takes the position that it is possible to maintain reasonable QoS levels without recourse to any of the class of constrained routing approaches (including MPLS), though Diffserv can be used with these approaches if desired.