在阅读hadoop权威指南的第四章时，我发现了以下句子：

In Hadoop, interprocess communication between nodes in the system is implemented using remote procedure calls (RPCs). The RPC protocol uses serialization to render the message into a binary stream to be sent to the remote node, which then deserializes the binary stream into the original message.

我知道我们在机器之间使用无密码ssh进行通信。
有人能解释一下我们用rpc或ssh来进行进程间通信吗？请澄清我的疑问。