A scalable architecture for end-to-end QoS provisioning Spiridon Bakiras * , Victor O.K. Li Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China Received 23 September 2003; revised 18 March 2004; accepted 13 April 2004 Available online 4 May 2004 Abstract The Differentiated Services (DiffServ) architecture has been proposed by the Internet Engineering Task Force as a scalable solution for providing end-to-end Quality of Service (QoS) guarantees over the Internet. While the scalability of the data plane emerges from the definition of only a small number of different service classes, the issue of a scalable control plane is still an open research problem. The initial proposal was to use a centralized agent, called Bandwidth Broker, to manage the resources within each DiffServ domain and make local admission control decisions. In this article, we propose an alternative decentralized approach, which increases significantly the scalability of both the data and control planes. We discuss in detail all the different aspects of the architecture, and indicate how to provide end-to-end QoS support for both unicast and multicast flows. Furthermore, we introduce a simple traffic engineering mechanism, which enables the more efficient utilization of the network resources. q 2004 Elsevier B.V. All rights reserved. Keywords: Admission control; Differentiated services; Quality of service; Resource management; Traffic engineering 1. Introduction In the past few years, the dramatic increase in the capacity of the Internet core, and the development of powerful compression techniques, have allowed the deployment of new applications such as Internet telephony, video-conferencing, streaming audio/video, etc. These applications are called real-time, since they require the periodic and timely delivery of the content from the source to the destination. Clearly, the traditional best-effort service that is provided in the current Internet cannot offer an acceptable level of service quality to this type of applications. To address this problem, the Internet Engi- neering Task Force (IETF) has proposed the Differentiated Services (DiffServ) architecture [1] as a scalable solution for providing end-to-end Quality of Service (QoS) guarantees over the Internet. The scalability issue is of outmost importance, since, in the future, the number of flows that will require some QoS guarantees is expected to be very large. Consequently, a core router should be able to accommodate thousands of QoS-sensitive flows at any time instant. The basic idea of the DiffServ architecture is that only edge routers should manage traffic on a per flow basis. Core routers should not keep any kind of per flow state, and should process traffic on a much coarser granularity. At the data plane this goal is achieved by specifying different Per Hop Behaviors (PHBs), where packets belonging to the same PHB form a Behavior Aggregate (BA) and receive identical service at the core routers. Specifically, the edge routers will be equipped with flow classifiers, policers, and markers that will properly mark the incoming packets by setting a number of bits on the DiffServ Codepoint (DSCP) [2] field of the IP packet header. The DSCP value will indicate the corresponding PHB, and the core routers will forward the packets based on their DSCP value (by utilizing several scheduling and buffer management techniques). The IETF has currently specified two different PHBs. The Expedited Forwarding (EF) PHB [3] offers the equivalent of a leased line (i.e. low delay, loss, and jitter) between a source and a destination. This is accomplished by giving EF traffic strict priority over the traditional best- effort traffic inside the DiffServ domain. However, each flow has to specify in advance the required bandwidth so that the appropriate resources may be reserved inside the network. In addition, the maximum burst size that is allowed is equal to two Maximum Transmission Units (MTUs). Computer Communications 27 (2004) 1330–1340 www.elsevier.com/locate/comcom 0140-3664/$ - see front matter q 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.comcom.2004.04.002 * Corresponding author. Tel.: þ 852-2857-8487; fax: þ 852-2559-8738. E-mail addresses: sbakiras@eee.hku.hk (S. Bakiras); vli@eee.hku.hk (V.O.K. Li).