CLASS-PINNING: A NOVEL APPROACH FOR HOP-BY-HOP QOS ROUTING Marília Curado, Orlando Reis, João Brito, Gonçalo Quadros, Edmundo Monteiro marilia@dei.uc.pt, {oreis, jbrito}@student.dei.uc.pt, {quadros, edmundo}@dei.uc.pt Laboratory of Communications and Telematics University of Coimbra Pólo II, Pinhal de Marrocos, 3030-290 Coimbra Portugal Abstract The need for Quality of Service (QoS) on the Internet is increasing everyday due to the wide dissemination of new communication services with more stringent demands from the network. There have been several proposals for QoS provisioning, particularly, the Integrated Services and Differentiated Services frameworks developed on the Internet Engineering Task Force (IETF). As the deployment of Differentiated Services on the Internet becomes a reality, it urges for its combination with QoS aware routing protocols. Among other proposals, at the Laboratory of Communications and Telematics of the University of Coimbra is being developed an intra-domain QoS routing protocol (UC- QoSR). In this paper a mechanism of class-pinning to integrate the UC-QoSR strategy is proposed and evaluated. This mechanism addresses the stability problem associated with congestion based routing by controlling the instant when a traffic class shifts to a new path. A traffic class is moved to a new path only if it is considerably better than the current path. Results show that with the use of class- pinning it is possible to maintain a adequate path for each traffic class and to avoid the instability due to frequent path shifts. Keywords: QoS routing, Differentiated Services, Stability 1 Introduction Quality of Service plays a major role in the deployment of communication system for applications with special traffic requirements, such as video-conferencing or Internet telephony. The need to support these types of traffic has motivated the communication research community to develop new approaches. Some of this work resulted in the Differentiated and Integrated Services architectures proposed by the IEFT [1, 2]. Current routing protocols used in the Internet lack characteristics for QoS provision to support emerging new services. All traffic between two endpoints is forwarded on the same path, even if there are other alternative paths with more interesting properties for the requirements of a specific flow or traffic class. Usually, it is selected the shortest path, based on a single static metric, that does not reflect the availability of resources. In these situations, congestion easily occurs on the shortest path, with the corresponding degradation of traffic performance, despite the underutilization of network resources on alternative paths. This scenario has motivated the development of QoS aware routing protocols. The most significant developments on QoS routing are aimed at communication systems where traffic differentiation is done per flow, as in the Integrated Services [3]. The Differentiated Services framework does not explicitly incorporate QoS routing. It is, thus, essential to develop QoS routing protocols for networks where traffic differentiation is done per class. The Quality of Service Routing protocol of the University of Coimbra (UC-QoSR) was conceived to fulfill this purpose. The UC-QoSR protocol selects the best path for each traffic class based on information about the congestion state of the network. This strategy extends the Open Shortest Path First (OSPF) protocol in order to select paths appropriate for all traffic classes [4, 5]. A prototype of UC-QoSR was implemented over the GateD platform, running on the FreeBSD operating system [6]. This prototype was used to evaluate the routing strategy according to communication and processing overhead. The measurements obtained showed that the overhead introduced was affordable by the