Distributed Computing: Introduction Department of Electrical & - - PDF document

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10/22/2009 Distributed Computing: Introduction Department of Electrical & Computer Engineering Rutgers University Definition of a Distributed System (1) A distributed system is: A collection of independent computers that appears to its

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Distributed Computing: Introduction

Department of Electrical & Computer Engineering Rutgers University

Definition of a Distributed System (1)

A distributed system is: A collection of independent computers that appears to its users as a single coherent system.

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Definition of a Distributed System (2)

A distributed system organized as middleware. Note that the middleware layer extends over multiple machines. 1.1

Distributed Systems

System where hardware/software components located at networked computers communicate and coordinate their actions only by message passing….

– Concurrency – No global clock – Independent failures – …

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Distributed Computing Issues

Heterogeneity

– Networks, hardware, OS, programming language, data representations, etc.

Interoperability: Middleware, mobile code, protocols

Openness

– Access, extendibility, …

Security

– Confidentiality, integrity, availabilty

Scalability Failure Handling

– Detecting failures, masking failures, tolerating failures, tolerating failures, recovery from failures, redundancy

Concurrency

– Consistency, causality, mutual exclusion, etc, ..

Transparency

Transparency in a Distributed System

Different forms of transparency in a distributed system.

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Openness

Openness means that a number of different platforms can be used in a network, all that is needed is some common protocol for them to communicate

Scalability Problems

Examples of scalability limitations.

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Scaling Techniques (1)

1.4 The difference between letting: a) a server or b) a client check forms as they are being filled

Scaling Techniques (2)

1.5 An example of dividing the DNS name space into zones.

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Clients and Servers

General interaction between a client and a server. 1.25

Processing Level

The general organization of an Internet search engine into three different layers 1-28

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Multitiered Architectures (1)

Alternative client-server organizations (a) – (e). 1-29

Multitiered Architectures (2)

An example of a server acting as a client. 1-30

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Modern Architectures

An example of horizontal distribution of a Web service. 1-31