The Desktop Grid offers solutions to overcome several challenges and to answer increasingly needs of scientific computing. This technology consists mainly in exploiting PC resources, geographically dispersed, to treat time consuming applications and/or important storage capacity requiring applications. However, as resources number increases, the need for scalability, self-organisation, dynamic reconfiguration, decentralization and performance becomes more and more essential. Since such properties are exhibited by P2P systems, the convergence of grid computing and P2P computing seems natural. In this context, this paper evaluates the scalability and performance of P2P tools for registering and discovering services (Publish/Subscribe systems). Three protocols are used in this purpose: Bonjour (définition), Avahi (définition) and Pastry (définition). We have studied the behaviour of these protocols related to two criteria: the elapsed time for registrations services and the needed time to discover new services. Our aim is to analyse these results in order to choose the most adequate protocol for creating a decentralized middleware for Desktop Grid.