Multiparty sessions are the basis of a wealth of applications. Some examples are audio/video conferencing, distance learning and gaming. Peer-to-peer ad hoc networks are now emerging. They are useful in a wide range of application scenarios in personal, commercial, public and military environments. Very little is known today on how to handle multiparty sessions in these new networks. This paper proposes a novel signaling system for multiparty sessions in peer-to-peer ad hoc networks. The architecture relies on clustering. Requirements are derived and new principles are proposed. The principles are implemented as extensions to the session initiation protocol (SIP). Extending SIP enables easy interworking with conventional third generation telecommunication networks. The implementation is presented. We have also built a prototype, using JXTA, a middleware for peer-to-peer. The prototype is described with the measurements we have made.