Explain the two fundamental models of inter process communication.

Two kinds of message passing system are given as:

(a) Direct Communication: Along with direct communication, each process which needs to communicate should explicitly name the recipient or sender of the communication. In this way, the send and receive primitives are explained as:

• send(P, message)- It send a message to process P.
• receive(Q, message)- It receive a message from process Q. The communication link in this scheme has the subsequent properties:
• A link is established automatically between every pair of processes that want to communicate. The processes require identifying only each other's know to communicate.
• A link is connected with exactly two processes.
• Certainly one link exists among each pair of processes.

(b) With indirect communication, the messages are sent to and received from mail-boxes or from ports. All mailboxes have a unique identification. In this method, a process can communicate with several other processes via a number of various mailboxes. Two processes can communicate only if they share a mailbox. The send and receive primitives are defined as given as below:

• send (A, message)- it send a message to mailbox A
• receive (A, message)- It receive a message from mailbox A. In this system, a communication link has the subsequent properties:
• A link is established among a pair of processes only if both members of the pair have a shared mailbox.
• A link may be connected with more than two processes.
• A number of various links may exist between each pair of communicating processes, along with each link corresponding to one mailbox.