Multiparty session types are a type system that can ensure the safety
and liveness of distributed peers via the global specification of their interactions.
To construct a global specification from a set of distributed uncontrolled
behaviours, this paper explores the problem of fully characterising multiparty
session types in terms of communicating automata. We equip global and local
session types with labelled transition systems (LTSs) that faithfully represent
asynchronous communications through unbounded buffered channels. Using the
equivalence between the two LTSs, we identify a class of communicating automata
that exactly correspond to the projected local types. We exhibit an algorithm
to synthesise a global type from a collection of communicating automata.
The key property of our findings is the notion of multiparty compatibility which
non-trivially extends the duality condition for binary session types.