Needed to be added to TierStore

It makes a big difference between having communication in one direction vs. having the possibility of a two way communication. The synchronization algorithm is a lot different, for example, it's much in two way communication it is possible for the synchronizing client to be able to resolve updates with its current state and request a diff of the changes. In one way communication, the server can only push out diffs and get an indication of the client state with a long latency.