Message Delivery Protocol

Message Delivery Protocol

· A protocol is a set of rules and conventions shared by communicating entities .

· Message passing can be blocking or non blocking .

· In blocking protocol, a sender process is blocked till the message selivered to the . in this case , sender process has guarantee that the message sent by it ie delivered before it continues its execution .

A blocking protocol normally includes:

1. Blocking send : the sender process is blocked until the message is received by the receiving process or by the mailbox.

2. Blocking receive : the receiver nlocks until a message is available thus when both sender as well as receiver is blocked ,it is known as rebdevezevous . this combination allows for tight sysnchronization between process.

· In non blockeing protocol, asender continues the execution after performing a send operation irrespective of whether the message is delivered or not

· A non blocking protocol has the advantage that a sender is free to continue its execution immediately after sending a message

· However , sender has no means of knoiwing when(and wheather )its message is delivered to the receiver.

· A non blocking send : the sending process sends the message and resumes operation.

· Non blocking receive: the receiver retrieves either a valid message or a null.

Buffering

Wheather the communication is direct or indirect , message exchanged by communicating processes reside in a temporary queue.

There are three different ways of implementing such queue.

Zero capacity

· Zero capacity queue cannot keep and message waiting in it , thus it has maximum length 0

· For this , sending process must be blocked until the receiving process receives the message .

· System with zero capacity queue is known as message system with no buffering.

Bounded capacity

· Bounded capacity queue has finite length n. thus it can have n message.

waiting in it .

· If the queue is not full , new message can be placed in the queue and the sending process is not blocked , it not blocked , it can continue execution without waiting.

· If the link or queue is full , then the sender must be blocked until space is available in the queue.

· This system is also known as automatic buffering .

Unbounded capacity

· Unbounded capacity queue has infinite length . thus any number of messages can wait in it .

In such a system , sending process is never blocked , can continue execution without waiting

Shared memory model

· Normally , process use memory areas within the scope of virtual memory space . also memory management systems ensure that every process has a well-defined and separate data and separate data and code area.

· In shared memory model parts of private address space of two or more rae processes are mapped to same physical memory.

· Such a memory areas are called shared memory regions.

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