View change

The view change protocol is inspired by the Synchronization Phase in this BFT-SMaRt paper. The view change protocol is comprised of three messages: ViewChange, ViewData, and NewView (Stop, StopData, and Sync in BFT-SMaRt).

The ViewChange message (the first message) is sent to all nodes by some node who suspects the leader is faulty. This message is very lightweight and includes only the next view sequence number. After recieving f+1 ViewChange messages, with the same view sequence number, the recieving node is convinced that at least one correct node is asking for a view change and so it helps it by sending the same ViewChange messages. Once recieving 2f+1 ViewChange messages the nodes will send a ViewData message to the next view's leader.