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					Enterprise Network Systems

Client/ Server Mark Clements

Last week . . .
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DWDM sends many different wavelengths simultaneously down SMF Many LASER LEDs used to supply light Distributed feedback LASERs commonly used Prism or diffraction grating separates colours PIN or APD used at receiver Fibre amplifiers used to boost signal
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This week . . .
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Client/ Server operation Characteristics of the software Characteristics of the hardware How client/ server delivers a web page Advantages and disadvantages of client/ server Examples of server softwares
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Client/ server interaction
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Distributed computing Powerful computer does work for many less powerful computers
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e.g. delivering a web page, searching a database

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Needs a network to operate Proactive service - client requests Server responds
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Overview of Client/ server

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Steps involved
1. A user of a computer will request a service using client software 2. The client software produces a request for the server software 3. The network delivers the request to the remote computer running server software

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More Steps
4. The remote computer uses the server software to accept the client request and to perform the requested task

5. The network is used to deliver the result of the request back to the client software
6. The client software displays the result to the user
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Division of Software
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Two parts of software
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Client or Front End Server or Back End or Daemon

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Protocol software is used to allow the softwares to communicate Internet uses TCP/ IP for communication between client and server

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Client Software
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An application program that uses a network to access a service is a client Client forms request
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keystrokes, mouse clicks

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Sends request & waits for reply Client software displays the results of the service
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Server Software
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This is reactive software Services client requests Runs 24hrs 7 days a week Run on high power computers usually
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high I/O, high memory and processing power e.g. FTP, web server
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Maybe several servers run on one machine
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Client characteristics
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Generally has a highly user-friendly interface Carries out editing tasks for the user Small hard disk required No need for high speed processor Contains client application software Must have a connection to a network

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Thin Client
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Specification for networked client Has little hardware May not have disks Relies on server for processing Accepts keystrokes, transmits Receives replies Displays results
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Why Thin Clients ?
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Reduces cost of hardware Reduce management costs Needed for new applications
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e.g. kiosk use
need windowed environment but not full PC power

New users
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Security from malware and downloading
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Server computer
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Mainframe, mini or high end PC Large storage area for data May use RAID technology Hot swappable disks Fast CPU(s), much RAM Does most of the data manipulation Multi-tasking
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Requesting a web page

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Client/ server advantages
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Less network traffic - data manipulation carried out at server
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only results passed to client

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Hardware savings No need for powerful clients If server upgraded, clients can remain same

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Client/ server disadvantages
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High initial hardware costs Both parts of software must be purchased Client software needs SQL capabilities if server has database to access Server database software very complex
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more so than stand - alone

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Types of server
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Web server - runs on computer to transmit web pages on request Runs HTTP Daemon Client software is browser Apache - 32 bit windows and UNIX Microsoft IIS

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File Server
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Holds LAN applications
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Clients use a central copy

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At upgrade, only need to upgrade 1 copy
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not 100s - at each client

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Access to shared storage, directories and files

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File server
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Controls exchange of files between network users Stops update problems Holds the operating system
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applications data

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Domain Name Service

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DNS Operation
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Translates Domain Names to IP numbers Similar to directory enquiries If data not available, request automatically forwarded to DNS that can Several hops may be needed to find appropriate DNS Reply allows your PC to form IP packet
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Print Server
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Handles organisation’s printing needs Accepts jobs from clients Forms queues (spooling) Sends print jobs to appropriate printer Can attach priorities to jobs May automatically redirect work to a free printer
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Conclusion
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Cost effective way of providing more computing power High specs for server hardware Thin client is cheap and often desirable Client is proactive, server reactive Client software is user friendly Must have a network to operate
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