distributed computing. computing? computing is usually defined as the activity of using and...
TRANSCRIPT
DISTRIBUTED COMPUTING
Computing?Computing is usually defined as the activity
of using and improving computer technology, computer hardware and software.
-wikipedia
Types of ComputingMonolithic DistributedParallelCooperative
Monolithic ComputingThe simplest form of computing, a single
computer, such as a personal computer(PC), is used for computing.
The computer is not connected to any network, and thus it may use only the resources within its immediate access. This form of computing is called Monolithic computing.
Monolithic ComputingExamples: Use of applications such as word
processing program or a spreadsheet on a pc.
Mainframe can be used a Monolithic Machine.
Multiple users can engage in monolithic computing.
The resources can be shared by concurrent users using technique known as “Time Sharing”.
Monolithic Computing
Main frameTerminals
Distributed ComputingDistributed Computing is performed in a
distributed system.
Distributed System is a collection of independent computers, interconnected via a network, that are capable of collaborating on a task. Computers are considered independent if they do not share memory or program execution space.
Distributed ComputingDistributed computing involves computing
performed among multiple network-connected computers, each of which has its own processor(s) and other resources.
A user, using a workstation , has full use of the resources on the local computer to which its workstation is connected as well may resources on the remote computers.
Distributed ComputingExample: The world wide web is an excellent
example of this type of computing.
When you use a browser to visit a web site, a program such as Internet Explorer runs on local system and interacts with a program(known as web server) which runs on remote system to fetch a file or resource.
Distributed ComputingCLIENT
SERVER
INTERMEDIATE HOSTS
Parallel ComputingParallel computing is typically performed on
a single computer that has multiple CPU’s.
It is also possible to compute by connecting the computers in a network but requires special software.
Parallel computingExample: weather forecasting,biology and
semiconductor design .
Cooperative ComputingCooperative Computing is done using
multiple computers for processing a task by sharing a problem into units between multiple computers.
Cooperative ComputingExample: Ebay Auctioning System
Strengths of Distributed ComputingAffordability and AvailabilityResource SharingScalabilityFault tolerance
Affordability and AvailabilityComputers connected to internet has become
universally available and generally affordable, the large number of interconnected computers makes for an ideal community for distributed computing.
Resource SharingThe architecture of distributed computing
mirrors the computing architectures of modern organizations.
Each organization independently maintains computers and resources that are local to the organization while sharing resources over the network.
ScalabilityDistributed computing provides scalability in
that increasing demand for resources can be addressed effectively with addition of resource required.
Fault toleranceDistributed computing provides the
opportunity for fault tolerance in that a resource can be replicated to sustain its availability in the presence of failures.
Weaknesses of Distributed ComputingMultiple points of failureSecurity concerns
Multiple points of failureThere are more points of failure in
distributed computing. Since multiple computers are involved, all of
which depend on the network for communication,the failure of one or more computers or one or more network links can cause trouble for distributed computing.
Security ConcernsIn distributed computing there are more
opportunities for unauthorized attack. The decentralization of control makes it
difficult to implement and enforce security policies, hence distributed computing is vulnerable for security breaches and unauthorized access.
Operating Systems ConceptsComputer Programs and processConcurrent Programming
Program & ProcessA software program is an artifact constructed
by a software developer using some form of programming languages.
When a program is “run” or executed, on a computer it is represented as a process.
Process State Transistion
Concurrent ProgrammingDistributed computing involves concurrent
programming, which is programming that involves the simultaneous execution of processes.Concurrent Processes executed on multiple
computersConcurrent Processes executed on a single
computer.Concurrent Programming in a process.
Multiple computersThe processes interact with each other by
exchanging data over the network, but their execution is otherwise completely independent.
Example:When you access a web page using a browser,
a process of the browser program, running on your machine interacts with the process running on the web server machine
Single ComputerModern computers are supported by
multitasking operating systems, which allow multiple tasks or processes to be executed concurrently.
Example:TimeSharing of a resource(such as CPU) by
player for some and by a compiler for some time.
In a ProcessConcurrent programming in separate
processes, it is often necessary for a single program to initiate tasks that are to be executed concurrently.
Example:It may be necessary for a program to perform
other tasks while waiting indefinitely for user input in one user interface window.(untill we press a key the program runs)
Parent and Child ProcessesAt runtime a process may spawn subordinate
processes or child process.
The process that spwans subordinate process is called Parent Process.
A Child process is a complete process, consisting of an executing program, its own current values, and state information, some of which is inherited from the parent process.
ThreadsA process may spawn threads, also known as
lightweight processes.
Threads carry a minimum of state information, but otherwise behave the same as processes.
They incur less overhead, threads are preferred over child processes.
Software EngineeringSoftware engineering is a discipline in
computer science that covers the process of developing applications.
The classes of building network applications are of two typesProcedural Object oriented
ProceduralThe C language is the primary example.
It uses procedures to break down the complexity of the tasks of an application.
An appplication is coded using a procedure or function.
Object-Oriented The example can be Java.
The problem is broken into objects and the messages between object.
Each object simulates an object in real life, carrying state data as well as behaviours.
State – Instance memberBehavior - Methods
UMLAn important step in the production of artifacts or documents to record the conceptual design of the application.
UML(Unified Modeling Language) is such a facility to provide common set of language notations for specifying, visualizing, constructing and documenting the artifacts of software systems.
Architecture of Distributed ApplicationsThe idea of using a multilayer architecture to
organize the functionalities of a data network can be applied to distributed applications.
FunctionalitiesThe functionalities of the distributed
applications can be classified in three layers:
Presentation LayerApplication Logic LayerService Layer
Presentation LayerIt provides the user interface.Example:
If the application is a shopping cart, this layer generates the set of web pages that are viewable by a shooper using a browser
Application Logic LayerIt provides the computation for the
application.Example:
This layer is responsible for such tasks as credit card verification and computing the dollar amounts of the orders,sales tax and delivery costs.
Service LayerIt provides the underlying services needed to
support the functionalities of the top two layers. Services may include data access facilities such as DBMS,DNS,IPC