What does Ensemble do that protocols like TCP/IP don ?
There is no answer to this question that is both short and complete. I’ll give a short one here; for a longer answer you can read the Horus technical reports, or visit other sites related to group communication. TCP/IP sockets work well for communication between pairs of processes. Ensemble can be viewed as a generalization of TCP communication to groups (i.e., one or more) of processes. TCP provides FIFO communication on point-to-point channels; Ensemble provides FIFO (and other more strongly ordered) channels between all members in a group. TCP alerts each endpoint when the other end has failed; Ensemble also detects failures and alerts all members of them (and guarantees that they all see the same set of failures). Other issues arise when groups of processes communicate instead of just pairs. Ensemble provides solutions to many of these. For instance, network outages can cause groups to partition. Ensemble detects these partitions, splits the group up, and automatically heals the gr
