Do we use RPC or SSH for inter process communication in hadoop? -

Do we use RPC or SSH for inter process communication in hadoop? -

while reading 4th chapter of definitive guide hadoop book, found next sentences :

in hadoop, interprocess communication between nodes in scheme implemented using remote procedure calls (rpcs). rpc protocol uses serialization render message binary stream sent remote node, deserializes binary stream original message.

and knew utilize password-less ssh communication amongst machines.

can explain me utilize rpc or ssh inter process communication? please clarify doubts.

hadoop deamons java processes, communicating through rpc. java objects go pass throgh network in serialized object form. ssh, or secure shell, protocol used securely log onto remote systems. mutual way access remote linux , unix-like servers, such vps instances

hadoop ssh rpc hadoop2