Enterprise Network Systems Client/ Server Mark Clements

25 Feb 2008ENS 2 Last week... 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

25 Feb 2008ENS 3 This week... 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

25 Feb 2008ENS 4 Client/ server interaction Distributed computing Powerful computer does work for many less powerful computers – e.g. delivering a web page, searching a database Needs a network to operate Proactive service - client requests Server responds

25 Feb 2008ENS 5 Overview of Client/ server

25 Feb 2008ENS 6 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

25 Feb 2008ENS 7 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

25 Feb 2008ENS 8 Division of Software Two parts of software – Client or Front End – Server or Back End or Daemon Protocol software is used to allow the softwares to communicate Internet uses TCP/ IP for communication between client and server

25 Feb 2008ENS 9 Client Software An application program that uses a network to access a service is a client Client forms request – keystrokes, mouse clicks Sends request & waits for reply Client software displays the results of the service

25 Feb 2008ENS 10 Server Software This is reactive software Services client requests Runs 24hrs 7 days a week Run on high power computers usually – high I/O, high memory and processing power Maybe several servers run on one machine – e.g. FTP, web server

25 Feb 2008ENS 11 Client characteristics 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

25 Feb 2008ENS 12 Thin Client Specification for networked client Has little hardware May not have disks Relies on server for processing Accepts keystrokes, transmits Receives replies Displays results

25 Feb 2008ENS 13 Why Thin Clients ? Reduces cost of hardware Reduce management costs Needed for new applications – e.g. kiosk use New users – need windowed environment but not full PC power Security from malware and downloading

25 Feb 2008ENS 14 Server computer 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

25 Feb 2008ENS 15 Requesting a web page

25 Feb 2008ENS 16 Client/ server advantages Less network traffic - data manipulation carried out at server – only results passed to client Hardware savings No need for powerful clients If server upgraded, clients can remain same

25 Feb 2008ENS 17 Client/ server disadvantages 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 – more so than stand - alone

25 Feb 2008ENS 18 Types of server 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

25 Feb 2008ENS 19 File Server Holds LAN applications – Clients use a central copy At upgrade, only need to upgrade 1 copy – not 100s - at each client Access to shared storage, directories and files

25 Feb 2008ENS 20 File server Controls exchange of files between network users Stops update problems Holds the operating system – applications – data

25 Feb 2008ENS 21 Domain Name Service

25 Feb 2008ENS 22 DNS Operation 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

25 Feb 2008ENS 23 Print Server 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

25 Feb 2008ENS 24 Conclusion 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