Q. Types of messages?

The messages can be of many types.  A specific field of all messages may be reserved to signify message type.  The message passing primitives are like this:

• Send (type, buffer, length, node process)
• Receive (type, buffer, length)

Where type recognizes message type buffer denotes location of message, length specifies length of message, node designates destination node and process signifies process ID at target node.  Transmit and receive primitives are used for indicating the transmitting and receiving processes correspondingly. The buffer field of send signifies the memory location from that messages are transmitted and buffer field of receive denotes space where arriving messages will be stored.