Question about handshake_receiver in IPC

Hi, I find before handle IPC, we always call handshake_receiver function. A basic question is why do we need to handshake receiver? What do we do when we handshake_receiver? Another thing I note is we have separate handshake_receiver (remote_handshake_receiver) if the receiver is on the other core. What is the difference between those two handshake_receiver functions? Thank you very much. Best, Yuixn