With the growth of the Internet and intranets, QoS technology that has been developed over a span of several years is quickly becoming more relevant. This article first defines QoS and introduces a taxonomy for QoS mechanisms. The evolution of several major QoS mechanisms is described with a special focus on RSVP and differentiated services. Special attention is paid to the role of the IETF in developing QoS mechanisms. We describe a QoS network that combines RSVP and differentiated services in a manner that realizes the benefits of each. We show that, in general, the adoption of increasingly sophisticated QoS mechanisms can enhance the ability of a network to offer high-quality service guarantees while simultaneously making efficient use of raw network resources. These mechanisms carry a cost in the form of increased overhead, which must be weighed against the benefits of the mechanism.
