distributed systems-a brief introduction

7/28/2019 Distributed systems-A Brief Introduction

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Distributed Systems

A Brief Introduction


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OUTLINE BRIEF HISTORY.

WHAT ARE DISTRIBUTED SYSTEMS ?

? WHY DISTRIBUTED SYSTEMS ? ?

ADVANTAGES OF D.S. OVER THE

CENTRALIZED SYSTEM. ADVANTAGES OF D.S. OVER

INDEPENDENT PCS.


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OUTLINE (Contd.) ORGANISATION OF DISTRIBUTED

SYSTEM.

GOALS OF D.S.

Resource Sharing.

Openness.

Transparency.

Scalability.


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OUTLINE (Contd.) Concurrency.

TYPES OF DISTRIBUTED SYSTEMS.

Distributed Computing Systems.

Distributed Information Systems.

Distributed Pervasive Systems. SUMMARY.


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HISTORY 1945~1985

Computers were large and expensive.

No way to connect them.

All systems were Centralized Systems.

Mid-1980s

Powerful microprocessors.

High Speed Computer Networks (LANs , WANs).


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HISTORY (Contd.)

Then came the

DISTRIBUTED

SYSTEMS


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What are Distributed Systems ? ?

A distributed system is a piece of software that

ensures that: a collection ofindependent computers appears

to its users as a single coherent system.

Two aspects:

(1) independent computers and (2) single

system => middleware.


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EXAMPLES World Wide Web (WWW) is the biggest

example of distributed system.

Others are

The internet

An intranet which is a portion of the internet

managed by an organization


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WHY DISTRIBUTED

SYSTEMS ? ?

availability of powerful yet cheap

microprocessors (PCs, workstations),

continuing advances in communication

technology


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ADVANTAGES OF D.S. OVER

CENTRALIZED SYSTEM: Economics:

A collection of microprocessors offer a better

price/performance than mainframes. Low

price/performance ratio: cost effective way to

increase computing power.

Reliability:

If one machine crashes, the system as a whole

can still survive. Higher availability and

improved reliability.


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ADVANTAGES (Contd.)

Speed: a distributed system may have more

total computing power than a mainframe.

Ex.: 10,000 CPU chips, each running at 50

MIPS. Not possible to build 500,000 MIPS

single processor.

Enhanced performance through loaddistributing.


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ADVANTAGES (Contd.)

Incremental growth: Computing power

can be added in small increments. This

leads to Modular expandability


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ADVANTAGES OF D.S. OVER

INDEPENDENT PCs:

Data sharing: allow many users to access

to a common data base.

Resource Sharing: expensive peripherals

like color printers.


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ADVANTAGES (Contd.)

Communication: enhance human-to-

human communication. E.g.: email, chat.

Flexibility: spread the workload over the

available machines


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ORGANIZATION OF D.S.:

A distributed system organized as middleware.

The middleware layer extends over multiple machines, and offers each

application the same interface.


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GOALS OF D.S. :

Resource Sharing.

Openness.

Transparency.

Scalability.

Concurrency.


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RESOURCESHARING: With Distributed Systems, it is easier for users to

access remote resources and to share resourceswith other users.

Examples: printers, files, Web pages, etc

A distributed system should also make it easier forusers to exchange information.

Easier resource and data exchange could causesecurity problemsa distributed system shoulddeal with this problem.


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OPENNESS:

The openness of DS is determined primarily

by the degree to which new resource-

sharing services can be added and be madeavailable for use by a variety of client

programs.


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TRANSPARENCY:

It hides the fact that the processes and

resources are physically distributed across

multiple computers.

Transparency is of various forms as

follows:


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TRANSPARENCY (Contd.)


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SCALABILITY:

A system is described as scalable if it

remains effective when there is a significant

increase in the number of resources and thenumber of users.

Challenges:

Controlling the cost of resources or money.

Controlling the performance loss.


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CONCURRENCY:

There is a possibility that several clients

will attempt to access a shared resource at

the same time.

Any object that represents a shared resource

in a distributed system must be responsible

for ensuring that operates correctly in aconcurrent environment.


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TYPES OF D.S. :

Distributed Computing Systems.

Cluster Computing Systems.

Grid Computing Systems.

Distributed Information Systems.

Distributed Pervasive Systems.


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DISTRIBUTED COMPUTING

SYSTEMS:

Goal: High performance computing tasks.

Cluster Computing Systems:

A supercomputer built from off the

shelf computer in a high-speed network

(usually a LAN)

Most common use: a single program is run

in parallel on multiple machines


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(Contd.)

Grid Computing Systems:

Contrary to clusters, grids are usually

composed of different types of computers

(hardware, OS, network, security, etc.)

Resources from different organizations are

brought together to allow collaboration

Examples: SETI@home, WWW


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DISTRIBUTED

INFORMATION SYSTEMS:

Goal: Distribute information across severalServers.

Remote processes called Clients access theservers to manipulate the information

Different communication models are used.

The most usual are RPC (Remote ProcedureCalls) and the object oriented RMI (RemoteMethod Invocations)


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(Contd.)

Often associated with Transaction systems

Examples:

Banks;

Travel agencies;

Rent-a-Cars; Etc


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DISTRIBUTED PERVASIVE

SYSTEMS:

These are the distributed systems involving mobile

and embedded computer devices like Small,

wireless, battery-powered devices (PDAs, smartphones, sensors, wireless surveillance cams,

portable ECG monitors, etc.)

These systems characterized by their instability

when compared to more traditional distributedsystems


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(Contd.)

Pervasive Systems are all around us, and ideallyshould be able to adapt to the lack of humanadministrative control:

Automatically connect to a different network;

Discover services and react accordingly;

Automatic self configuration (E.g.: UPnP

Universal Plug and Play) Examples: Home Systems, Electronic Health

Care Systems, Sensor Networks, etc.


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SUMMARY

Distributed systems are everywhere

Internet, intranet, wireless networks.

Resource sharing is the main motivating

factor for constructing distributed systems.

The construction of distributed systems

produces many challenges like Securecommunication over public networks.

distributed systems-a brief introduction

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