Basic Structure of Message System

In this topic, you will learn about, Basic Structure of the Message System.

Basic Structure of Message-System: The function of a message system is to allow processes to communicate with each other without the need to resort to shared variables.

An IPC facility provides at least two operations:

  1. Send (Message) and
  2. Receive (Message).

If two processes P and Q want to communicate, they must send messages to and receive messages from each other that is a communication link must exist between them.

For logical implementation some basic implementation questions are:

  1. How are links established?
  2. Can a link be associated with more than two processes?
  3. How many links can there be between every pair of processes?
  4. What is the capacity of the link?
  5. What is the size of messages?
  6. Is the link Uni-directional or bi-directional?

In Addition, there are several methods for logically implementing a link and the send/receive operation:

  1. Direct and indirect communication.
  2. Symmetric and asymmetric communication.
  3. Automatic or explicit buffering.
  4. Send by copy or send by reference.
  5. Fixed-size or variable size message.

Buffering: A link has some capacity that determines the number of messages that can reside in it temporarily. This property can be viewed as a queue of messages attached to the link. Basically, there are three ways that a search for a queue can be implemented.

Exception Condition: A messaging system is particularly useful in a distributed environment, where processes may reside at different sites. In such an environment, the probability that an error will occur during communication Is much larger than in a single machine environment.

See also  Exception Condition

When a failure occurs in either a centralized or distributed system, some error recovery must take place.

Some of the exception conditions that a system must handle in the context of a message system are:

  1. Process terminates.
  2. Lost messages.
  3. Scrambled messages.
  4. Three ways handshaking.
  5. Sliding window.
  6. Transmission impairments.

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