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+
+
+Architecture
+
+TMCast (stands for Transaction MultiCast) is an implementation of a
+transactional multicast protocol. In essence, the idea is to represent
+each message delivery to members of a multicast group as a transaction - 
+an atomic, consistent and isolated action. A multicast transaction can
+be viewed as an atomic transition of the group members to a new state. 
+If we define [Mo] as a set of operational (non-faulty) members of the 
+group, [Mf] as a set of faulty members of the group, [Ma] as a set of 
+members that view transition [Tn] as aborted and [Mc] as a set of members 
+that view transition [Tn] as committed, then this atomic transition [Tn]
+should satisfy one of the following equations:
+
+Mo(Tn-1) = Ma(T) U Mf(T)
+Mo(Tn-1) = Mc(T) U Mf(T)
+
+Or, in other words, after transaction T has been committed (aborted), 
+all operational (before transaction T) members are either in the
+committed (aborted) or failed state.
+
+Thus, for each member of the group, outcome of the transaction can
+be commit, abort or a member failure. It is important for a member
+to exhibit a failfast (error latency is less than transaction cycle) 
+behavior. Or, in other words, if a member transitioned into a wrong 
+state, it is guaranteed to fail instead of delivering a wrong result.
+
+In order to achieve such an error detection in a decentralized 
+environment, certain limitations were imposed. One of the most 
+user-visible limitation is the fact that the lifetime of the group 
+with only one member is very short. This is because there is not way 
+for a member to distinguish "no members yet" case from "my link to the
+group is down". In such a situation, the member assumes the latter case. 
+There is also a military saying that puts it quite nicely: two is one, 
+one is nothing.
+
+
+State of Implementation
+
+The current implementation is in a prototypical stage. The following 
+parts are not implemented or still under development:
+
+* Handling of network partitioning (TODO)
+
+* Redundant network support (TODO)
+
+* Member failure detection (partial implementation)
+
+
+Examples
+
+There is a simple example available in examples/TMCast/Member with 
+the corresponding README.
+
+
+-- 
+Boris Kolpackov <boris@dre.vanderbilt.edu>