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Enterprise Network Systems
Client/ Server
Mark Clements
25 Feb 2008 ENS2
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 2008 ENS3
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 2008 ENS4
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 2008 ENS5
Overview of Client/ server
25 Feb 2008 ENS6
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 2008 ENS7
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 2008 ENS8
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 2008 ENS9
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 2008 ENS10
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 2008 ENS11
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 2008 ENS12
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 2008 ENS13
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 2008 ENS14
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 2008 ENS15
Requesting a web page
25 Feb 2008 ENS16
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 2008 ENS17
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 2008 ENS18
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 2008 ENS19
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 2008 ENS20
File server
Controls exchange of files between network users
Stops update problems Holds the operating system
– applications
– data
25 Feb 2008 ENS21
Domain Name Service
25 Feb 2008 ENS22
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 2008 ENS23
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 2008 ENS24
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