SPAD: A distributed middleware architecture for QoS enhanced alternate path discovery Thierry Rakotoarivelo a,b,c, * , Patrick Se ´nac b,d , Aruna Seneviratne c , Michel Diaz d a School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, NSW 2052, Australia b Department of Applied Mathematics and Computer Engineering, ENSICA, Place Emile Blouin, 31056 Toulouse, France c National ICT Australia, Locked Bag 9013, Alexandria, NSW 1435, Australia d LAAS-CNRS, 7 avenue du Colonel Roche, 31077 Toulouse, France Abstract In the next generation Internet, the network will evolve from a plain communication medium into one that provides endless services to the users. These services will be composed of multiple cooperative distributed application elements. We name these services overlay applications. The cooperative application elements within an overlay application will build a dynamic communication mesh, namely an overlay association. The Quality of Service (QoS) perceived by the users of an overlay application greatly depends on the QoS experienced on the communication paths of the corresponding overlay asso- ciation. In this paper, we present super-peer alternate path discovery (SPAD), a distributed middleware architecture that aims at providing enhanced QoS between end-points within an overlay association. To achieve this goal, SPAD provides a complete scheme to discover and utilize composite alternate end-to-end paths with better QoS than the path given by the default IP routing mechanisms. Keywords: Quality of Service; Overlay networks; Peer-to-peer; Service-oriented networks; Middleware 1. Introduction In recent years, the presence of mobile network- enabled devices in our environment has steadily increased. These devices will collectively form a per- vasive computing and networking environment around the users, informing them, satisfying their communication needs, and performing various tasks on their behalf. In that regard, it might be unrealis- tic to assume that these portable devices will be capable of providing the increasing and extensive local applications, computing or storage resources that the users will require. In contrast, it might be more realistic to rely on service providers at the edge of the network to provide the required resources in a * Corresponding author. Address: National ICT Australia, Locked Bag 9013, Alexandria, NSW 1435, Australia. Tel.: +61 2 8374 5245; fax: +61 2 8374 5531. E-mail addresses: thierry@mobqos.ee.unsw.edu.au (T. Rako- toarivelo), senac@ensica.fr (P. Se ´nac), Aruna.Seneviratne@nic- ta.com.au (A. Seneviratne), Michel.Diaz@laas.fr (M. Diaz).