Distributed System

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MZUZU UNIVERSITY

FACULTY OF INFORMATION SCIENCE AND COMMUNICATIONS

DEPARTMENT OF INFORMATION AND COMMUNICATION TECHNOLOGY

 COURSE TITLE: DISTRIBUTED SYSTEMS

COURSE CODE: ICT3604

FROM: CHIMWEMWE SHABA

(PGDICTU/2B/11/15)

TO: MR REUBEN MOYO

TASK: MAKING SUMMARY

DATE: 07/07/2017

SUMMARY

Chapter 1: Introduction 

Definition

Distributed system refers to a collection of independent computers that looks like a single coherent system.

Characteristics of Distributed System

1. The differences between various computers and the ways in which they communicate are mostly hidden to the users.
2. Users and applications can interact with a Distributed System in a consistent and uniform way, regardless of where and when interaction takes place
3. Distributed System should be able to expand or scale

• Distributed systems are organized by the means of layer of software that is logically placed between high-level layer comprising users and applications and the layer below consisting of operating systems and basic communication facilities called middleware.
• All this aim at supporting heterogenous computers and networks while offering single-system view.

GOALS

The main goals of distributed system are

1. Should make resource easily accessible
2. Should be transparent- meaning should be able to hide resources
3. Should be open
4. Should be scalable- should give room for addition

1. Making Resources Accessible

Main goal of distributed system is to make it easy for the users access remote resources and share them in a controlled and efficiency way.

Reasons for sharing:

1. For economic reason
2. For easy collaboration and exchange information

1. Transparency

Distributed system is said to be transparent if it present itself to users and applications as it was single computer system

Types of Transparency

1. Access transparency
2. Location transparency
3. Migration transparency
4. Relocation transparency
5. Replication transparency
6. Concurrency transparency
7. Failure transparency

1. Openness

An open distributed system is the systems that provide services according to standard rules that describe the syntax and semantics of those services.

Goals for open distributed system are:

1. Proper specifications are complete and neutral
2. Easy to configure the system out of different components

1. Scalability

System can be scalable with:

1. Respect to its size
2. Geographically
3. Administratively

Scalability Problems

1. Centralized services
2. Centralized data
3. Centralized algorithm

Note: When developing distributed system do not the following assumptions:

1. Network is reliable
2. Network is secure
3. Network is homogenous
4. Topology does not change
5. Latency is zero
6. Bandwidth is infinite
7. Transport cost is zero
8. There is one administrator

Types of Distributed system

1. Distributed Computing system

Subdivided into:

1. Cluster computing system
2. Grid computing system

1. Distributed information processing system

Primitives of Distributed processing system

1. Begin-transaction
2. End-transaction
3. Abort transaction
4. Read transaction
5. Write

Characteristics of Transaction Processing system

1. Atomic
2. Consistent
3. Isolated
4. Durable

1. Distributed Pervasiveness system

Requirements

1. Embrace contextual change
2. Encourage adhoc composition
3. Recognize sharing as adefault

CHAPTER TWO-

Architecture

Organization of distributed system is mostly about the software components that constitute the system.

These softwares help us to know how different software components are to be organized and how they should interact.

Architectural Styles

There are several architectural styles (logical styles). Important ones are:

1. Layered architectures

-components organized in layered fashion

-requests go down the hierarchy while results flow upward

1. Object base architecture

-far loose organization follow this style

1. Data centred architecture

-evolve around the idea that process communicate through a common (passive or active) repository

1. Event based architecture

-processes communicate through the propagation of events

-sometimes carry data

System Architectures

Important styles of hardware architecture for distributed system are

1. Centralized Architecture

-in this one there are

        1. basic client-server

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