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