Update 0004_ws2p_v1.md

rfc/0004_ws2p_v1.md

@@ -288,6 +288,27 @@ Real example :
 
 ### HEAD Rebound policy
 
+#### Local HEAD
+
+The local node issues a new HEAD every time the last block of its local branch changes, this change can have two causes:  
+1. Arrival of a new block valid and stackable on the local branch
+2. Local branch change caused by the fork resolution algorithm
+
+Each time the local node emits a new head, it sends it to all established ws2p connections.
+
+### Remotes HEADs
+
+When the local node receives a HEAD message, it checks whether all of the following conditions are verified : 
+
+1. The head has a valid format and a valid signature  
+2. The head has a block number equal to or greater than all cached heads for the same ws2pid  
+3. If the block number is equal to the cached head, the head is of a higher or equal version.  
+4. If the block number is equal to the cached head, and the version is identical, the step field is smaller.
+
+If all these conditions are respected, perform the following actions:  
+1. Save this head in the headCache, overwrite the existing head if it exists.  
+2. Increment the step field of this head then send it to all established ws2p connections.
+
 ### Documents rebound policy