A. Aagesen et al. (Eds.): INTELLCOMM 2004, LNCS 3283, pp. 151–159, 2004. © IFIP International Federation for Information Processing 2004 Design Principles of a QoS-Oriented Transport Protocol Ernesto Exposito 1 , Michel Diaz 2 , and Patrick Sénac 2,3 1 NICTA, NPC Program, Locked Bag 9013, Alexandria, NSW 1435, Australia ernesto.exposito@nicta.com.au 2 LAAS/CNRS, 7 avenue du Colonel Roche, 31077 Toulouse cedex 04. France michel.diaz@laas.fr 3 ENSICA, DMI 1 Place Emile Blouin 31056, Toulouse Cedex, France patrick.senac@ensica.fr Abstract. In this paper, the needs for specialized end-to-end communication ser- vices oriented to satisfy the QoS requirements of current and future multimedia applications are raised. Face to the complexity involved in the wide deployment of QoS guaranteed network services as well as the reduced set of services offered by traditional and recent transport protocols, a QoS-oriented transport protocol (QoSTP) is proposed as the adequate solution for common Internet users for next few years. The design of this QoSTP is based on a set of fundamental principles aimed at assuring the feasibly and efficient deployment of adequate mechanisms regarding the applications requirements. Experimental results demonstrate the fea- sibility and advantages of this proposal. 1 Introduction Traditional and new generation of transport protocols have been designed taking into account only a subset of the QoS requirements of multimedia applications. Indeed, these protocols have been mainly focused to the implementation of congestion control mechanisms to save network resources (i.e. TCP, SCTP and DCCP) while providing full order and full reliability or non order and non reliability at all. Moreover, mecha- nisms intended to satisfy time constraints are not supported at the transport layer. A QoS oriented transport service based on the delay, jitter, throughput and synchroniza- tion constrains of multimedia applications and taking into account the partial order and partial reliability tolerance as well as the scalable characteristics of multimedia flows has not yet been provided. In addition, at the network layer, even if a lot of research aimed at the provision of end-to-end QoS guarantees has been carried out, today and for the next few years, the Best-Effort service will be the predominant and more accessible network service in Internet. These are the reasons that led us to propose the design of a QoS-oriented transport protocol (QoSTP). This design has to be based on a set of fundamental principles aimed at assuring the feasibly and efficient deployment of adequate transport mecha- nisms regarding the applications requirements. This paper is organized as follows. Next section introduces the design principles of this QoSTP. Sections 3 and 4 describe respectively the API and the mechanisms of