  There is a wide variety of message-passing communication models, ranging from
synchronous ''rendez-vous'' communications to fully asynchronous/out-of-order
communications. For large-scale distributed systems, the communication model is
determined by the transport layer of the network, and a few classes of orders
of message delivery (FIFO, causally ordered) have been identified in the early
days of distributed computing. For local-scale message-passing applications,
e.g., running on a single machine, the communication model may be determined by
the actual implementation of message buffers and by how FIFO queues are used.
While large-scale communication models, such as causal ordering, are defined by
logical axioms, local-scale models are often defined by an operational
semantics. In this work, we connect these two approaches, and we present a
unified hierarchy of communication models encompassing both large-scale and
local-scale models, based on their concurrent behaviors. We also show that all
the communication models we consider can be axiomatized in the monadic second
order logic, and may therefore benefit from several bounded verification
techniques based on bounded special treewidth.
