A review of quality of service mechanisms in IP-based networks — integrated and differentiated services, multi-layer switching, MPLS and traffic engineering

Abstract

ISPs are facing the challenge of offering improved quality of service (QoS) to their customers. No longer is best effort delivery with no service guarantee acceptable for many applications. Although ATM has provided a limited solution by way of service classes, such a solution pre-supposed an underlying ATM network which — in the case of pure IP traffic — may not be the case. Rather IP traffic requires a degree of engineering into service classes (differentiated services, DiffServ) as well as a break from traditional layer three-based routing. Although access to virtually unlimited bandwidth via WDM and Photonic Networks may potentially offer a solution to the QoS issue, access to such services on a universal basis is not a services class paradigm and using a label switching technique is seen as an appropriate medium term solution. Further, label switching offers a simple and efficient mechanism for IP traffic engineering, multi-service functionality and scalability. This paper examines a number of service classifications and solutions, which aim to provide a realistic QoS solution. In particular it addresses Integrated and DiffServ, multi-layer switching and MPLS, which forms the basis of DiffServ as it allows ISPs to deliver new services not easily supportable by conventional IP routing infrastructure. Finally the paper makes some important observations about traffic engineering.