When a new process joins a group, it needs to be updated with the current state of the application. Similarly, when two partitions of the same group merge, they often need to agree on a common state before normal operation can proceed. The XFER layer provides for this state merge or state transfer. It adds a phase to a membership change, in which processes can exchange state information. The XFER layer detects and notifies termination of this transfer. In the simplest and most common case, this consists of a contact member of the primary partition of the group transfering all its state to the set of new or non-primary members. In more complex cases a simple termination detection algorithm is necessary to detect completion of the merge.