Indirect Communication
Sending and receiving messages in a group can be either the easiest thing in the world or the most complicated; it all depends on what we guarantee.
Indirect communication is central in distributed systems yet very hard to get right. It is often provided in a middlelayer that hides the implementation details. Nevertheless one needs to understand what the problem is and how things are solved in order to use the tools efficiently.
Read chapter 6 in the course book.