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In t rod uct ion t o Dist r ibu t edSystems

Dhav al Jo shiAssistant ProfessorM .Sc.(I.T./ I.C.T.) Pro gram m e,Veer Narm ad Sou th Gujarat Universi ty ,Surat.

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Dist r ib u t ed Syst em s

Definition :

A system in which H/W and S/W

components located at networked computers

communicate and coordinate their actions

only by passing messages.

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W hy Dist r ib u t ed Syst em ?

Sharing resources and ensuring availability of it.E.g. :

1)Hardware like printer, camera, disk space, etc.

2)Information and Communication like databases,files, mobile phones, etc.

3)Media and Entertainment like music, video, etc.

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Exam p les o f Dist r ib u t ed Syst em s

Internet

Intranet

Mobile and Ubiquitous Systems

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In ternet

Large interconnected collection ofcomputers

Interaction is via message passing

Various Protocols help with messages

IP

TCP

UDP

FTP

HTTP

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In ternet

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In t ranet

Po rt io n o f t h e In t er net t h at is sep ar at e ly

ad m in ist rat ed an d has a b o un d ary t o

co n figur ed t o enf o rce local securi t y po l icies.

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In t ranet

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M ob ile and Ub iqu i t ou s com pu t ing

It is t h e h ar n essin g o f m an y sm all, ch eap

com pu t at iona l dev ices t ha t are p resen t in

users ph ysical envi ro nm ent .

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M ob ile and Ub iqu i t ou s com pu t ing

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Challenges o f Dist r ibu t ed Syst em s

Heterogeneity

Openness

Security Scalability

Failure handling

Concurrency

Transparency

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Heterogenei ty

System must work on different networks, hardware,OS, Programming Language and alsoimplementation by different people.

It can be done by using proper standards.

Middleware programming abstraction as well asmasking the heterogeneity.

Like mobile code (Applets) and virtual machine.

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Openness

Extensib i l i ty The system can be extended andre- im plem ent ed in var ious w ays.

I t sh ou ld al lo w n ew ad d it ion in syst em l ike,

New H/ W m ore com put ers,

S/ W sup po rt of n ew f i le fo rm at ,

Services and

Sharing resources.

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Security

Con f ident ial it y pr ot ect ion against d isclosur e t ounauthor ized indiv iduals.

In t e gr it y p r o t ect i on again st alt e rat i on an dcor rup t ion .

Avai lab i li ty pro t ect ion against in t er feren ce w i tht h e m eans t o access t he r eso u rces.

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Scalability

Remain effective when there are significantincrease in number of resources and users.

Controlling the cost of physical resources.

Controlling the performance loss.

Preventing resources from running out.

Avoid performance bottlenecks.

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Failur e Hand l ing

Failure detection is partial and also difficult.Detecting failure few are impossible todetect.

Masking failure retransmission

Tolerating failure

Recovery from failure role back in DB

(Transaction)

Redundancy duplicate data

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Concurrency

Services and resources are shared by the c l ientsin a d ist r ib u t ed syst em s.

Co rr ect syn chro n izat ion is essen t ial.

e.g. On l ine Sh o pp ing

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Transparency

Concealment of the distributed nature ofsystem from user or programmer.

Access Transparency

Location Transparency

Concurrency Transparency

Replication Transparency

Failure Transparency

Mobility Transparency