Peer-to-peer networks and other many-to-many relations have become popular especially for content transfer. To better understand and trust these types of networks, we need formally derived and verified models for them. Due to the large scale and heterogeneity of these networks, it may be difficult and cumbersome to create and analyse complete models. In this paper, we employ the modularisation approach of the Event-B formalism to model the separation of the functionality of each peer in a peer-to-peer network from the network structure itself, thereby working towards a distributed, formally derived and verified model of a peer-to-peer network. As coordination aspects are fundamental in the network structure, we focus our formalisation effort in this paper especially on these. The resulted approach demonstrates considerable expressivity in modelling coordination aspects in peer-to-peer networks.