Wireless network

• Usually use Radio Frequency (RF) technology– transmit and receive data over the air

• Adv :– providing all the features of wired LAN– without the limitations of a cable

• Disadv :– lower transmission speed– higher cost (when c.f. wired network)

• Wireless LAN– usually used in complement with a wired LAN– becoming an alternative for wired LAN

• by means of an access point (AP)– a device that transports data between a wireless LAN

and a wired LAN– with wireless LAN Card

» wireless network interface card» wireless node

• with area of coverage

• One of the advantage of Wireless LAN– provide mobility

• suitable for – school campus– taking inventory in a warehouse– making order for a restaurant– hospitals– construction site– temporarily office – health care ; retail ; manufacturing ; warehousing

; education

Network Topology

• Network Topology = logical layout or the way in which the computers and other network devices are connected

• Each computer / device = node

• Common Topologies– Bus topology– Star topology– Ring topology

• Bus Topology– all computers and other network devices

are connect to a single central cable

– Adv :• Easy to set up• failure of one device does not affect the rest of th

e bus network

– Disadv :• failure of any point on the central bus may lead to

the failure of the whole network• only one PC can send data on a bus network

– therefore number of computer attached to the bus will affect the performance of network

» more PC, more waiting, slower the network

– 3 concepts about Bus Topology• sending the signal• signal bounce (CSMA / CD)• terminator

• Sending the signal– in form of electronic signals– sent to all computers on the network– only the computer whose address matches the address

encoded in the original signal accepts the information– all other PC reject the data

• Signal Bounce– as data is sent to the entire network– travels from one end of the cable to the other– if signal is allowed to continue uninterrupted– signal will keep bouncing back and forth– other PC cannot send signals– therefore signal must be stopped after it has a chance to

reach the proper destination address

• Terminator– to stop the signal from bouncing– a component called a terminator

» placed at each end of the cable» to absorb free signals» to clear the cable so that other PCs can send data

– both end should plug with terminator

• Star Topology– all the devices on the network

• connect to a central device (hub / switch / router)– thus forming a star

– if one device / computer fail• not affecting the others.

– If the connecting cable between an device and the central device fail / has problem

• not affecting the others

– If the central device fails– power / networking problem

• the entire network is not working

– Star topology is the most common type of network topology

– Advantage :• centralized resources• centralized management

– Disadvantage :• great deal of cable in a large network installation• if central point fail, the entire network goes down

– One PC fail• if one PC, or one of the cable that connects it to

the hub fails (on a star network)• only the failed computer will not be able the

– send, or– receive network data

– no bouncing and terminator

• Ring Topology– all the devices are connected on a circular

path – data flows in only one direction– For sending data

• data travels to each computer on the ring until it reaches its destination

– control data transmission by using• token-passing scheme

– Token• control signal passes from one device to the next

– indicating which device is allow (has the right) to transmit signal

– thus ensure the only one computer at a time can transmit data

– therefore, no data collision

– Disadv : • if a device on a ring network fail / cable fail

– whole network fail

• Topologies :– usually more than 1 topology is used in a

network• For example : school network

– bus + star

Network Operating System

• Desktop Operating System– e.g. Windows 98 / ME

• good to use• with necessary software for establishing

communication with a network server

– But if want to • manage network resources• control the flow of data• maintain security …………….. !!!!!!!!

– Thus need a Network Operating System (NOS)

– NOS :• has 2 components :

– Network Server Software– Network Client Software

– Network Server Software– e.g. Mac OS X Server / Windows .NET Server

• control file access from the server’s hard disk

• manage print queue

• tracks user data such as user Ids and passwords

– Network Client Software– Mac OS X, Windows XP Professional

• gather login information

• handles drive mapping

• directs printouts to the network printers