There are different models for establishing a connection between two programs.
One is called a “client”, and the other is a “server”. In general, the “client” program makes a request and the “server” responds to this request. It is an “asymmetrical” architecture which passes through a central server.
Berty uses a symmetrical model called peer-to-peer (P2P), in which it is the responsibility of both programs to play the roles of both the client and the server. Giving each program both roles allows an anonymous exchange between them, without personal information passing through a server.