Direct vs Indirect communication and Synchronous vs Asynchronous Communication?
In direct communication, it gives the name of the process you are communicating with such as send(destination-process, message) and receive (source-process, message). A link has exactly one pair of communicating processes. Between each pair there exists exactly one link, which may be unidirectional, but is usually bidirectional.
Indirect communication has a unique ID, processes can communicate only if they share a mailbox, also known as ports. During communication a link is established only if processes share a common mailbox. The link may be associated with many processes, and each pair of processes may share several communication links that can be either bi or unidirectional
Synchronous is considered blocking. A blocking receive has the receiver block until a message is available and a blocking send has the sender block until the message is received. For a blocking send/receive, that is called a rendezvous.
Asynchronous is also called non-blocking. For an asynchronous/non-blocking send has the sender send a message and continue. For a non-blocking receive, it has the receiver receive a valid message or it becomes null.
