Total Order Multicast

This one of the most useful primitives for group communication. This ensures that messages sent to a group will be delivered to all members in the same order.
Assume process A sends messages x and y to processes B and C.
In total order multicast, processes B and C will receive the messages in the same order as process A send them.
This is also called as locally total multicast.

Total order multicast can be implemented,
                1. Using a sequencer
                                   – One dedicated “sequencer” that orders all messages
                                   – Everyone else follows.
                2. ISIS system
                                   – Similar to having a sequencer, but the responsibility is distributed to each                                             sender.

Total Ordering Using a Sequencer 

ISIS algorithm for total ordering

 • Sender multicast message to everyone
 • Reply with proposed priority (sequence no.)
           – Larger than all observed agreed priorities
           – Larger than any previously proposed (by self) priority
• Store message in priority queue
           – Ordered by priority (proposed or agreed)
           – Mark message as undeliverable
• Sender chooses agreed priority, re-multicast message with agreed priority
           – Maximum of all proposed priorities
• Upon receiving agreed (final) priority
           – Mark message as deliverable
           – Deliver any deliverable messages at the front of priority queue

Distributed Systems

A distributed system is a collection of autonomous computers that connected through a network and a distributed middleware which enables computers to coordinate their activities and to share the resources of the system, so that users perceive the system as a single, integrated computing facility.

Distributed system Vs Centralized system

In centralized systems, it directly control the operation of the individual units of information from a single center.This a master slave based model.This control the operations of the individual units and the flow of information from a single center.

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Introduction

In the computer industry, middleware is a general term for any programming that allows two already existing and separate programs to mediate together.

Middleware architecture is an increasingly familiar topic in enterprise IT. The term middleware is used to define the software that interacts between a network and a database and also in similar situations. Now its term has a border meaning and we can tell it as the very networks that allow the software to run on other devices. Middleware make it easier for the software developers to perform communication and input/output as they can focus on the specific purpose of the application. Middleware is the software layer that is between the applications and the operating system on each side of a distributed computer network.