Providing innovating multimedia services is a high priority for service providers. Due to the high traffic volume created by multimedia content, the use of decentralised services can lead to better solutions. Starting from the ongoing work of P2PSIP, we define a simple way to interconnect different domains using peer-to-peer networks. We define the needed signalling to provide connectivity between different domains based on P2PSIP. This fact allows an easier deployment of global decentralised multimedia services. We validate the proposed solution through an analytical and experimental study of the routing performance and routing state for two possible scenarios.