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:
- Send (Message) and
- 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:
- How are links established?
- Can a link be associated with more than two processes?
- How many links can there be between every pair of processes?
- What is the capacity of the link?
- What is the size of messages?
- Is the link Uni-directional or bi-directional?
In Addition, there are several methods for logically implementing a link and the send/receive operation:
- Direct and indirect communication.
- Symmetric and asymmetric communication.
- Automatic or explicit buffering.
- Send by copy or send by reference.
- 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.
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:
- Process terminates.
- Lost messages.
- Scrambled messages.
- Three ways handshaking.
- Sliding window.
- Transmission impairments.
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