1. Networks
“Each time you use the telephone you use the world’s largest computer network – the telephone system”

2. A Computer Network
A system of linked computers that allow messages to be transmitted from one to another
Messages can be text, sound, video and graphics

3. Purpose of Networks Allows sharing of hardware
Allows sharing of software
Allows easy exchange and sharing of data between different locations
Tele-working
Video Conferencing
Electronic data interchange (EDI)

4. Components of a Network
Hardware
A sending device
A communications link
A receiving device
Communications software

5. Network Terms Node Channel Host Computer (Server)
A point on a network to which a device is attached
Channel
The path over which data is transmitted
Host Computer (Server)
A computer that manages the network

6. Types of Networks There are 2 basic types of networks
LAN – Local Area Network
WAN – Wide Area Network

7. LAN ‘Hardwired’ within the same building
Components are in fixed positions
Computers are in close ‘proximity’ to each other
Computers have immediate access to CPU – no dial-up required
Terminals/computers are directly linked to each other and to the host computer

8. WAN
Uses a telecommunications service to link computers over a distance
Needs a modem to convert signals from digital to analog for transmission
May use a combination of telecommunications services
Connects many types of computers

9. Hardware Required Network Card Cables/wires for interconnection
Modem to convert signals
Satellites to relay data
Microwave stations to relay data

10. Network Card (NIC)
Network card also called a Network Interface Card (NIC)
NICs are needed to connect the network cable to the computer

11. Communications Channel
The route for digital information to pass through the network
Wired and wireless
The channel capacity is the number of bits of information it can transmit per second

12. How is Data Transmitted?
Both LANS and WAN use the following to link computers
Twisted pair wire
Coaxial Cable
Fiber-optic cable

13. Twisted Pair Wire
Two copper wires are twisted together to form a cable and then insulated
Inexpensive
Used in normal telephone lines so are already in place in buildings
Susceptible to noise or interference
Slow data transmission

14. Coaxial Cable Used to connect computers and terminals in a LAN
Heavily insulated single wire
Can be laid underground or under the sea
Much faster data transmission than twisted wire
Less interference than twisted wire

15. Fiber Optic Cable
Fiber optic technology uses light, not electricity, to send data
Cables are made of glass fibers that guide light beams for miles
Fiber optics is faster, lighter, and less expensive than wire cables

16. Fiber Optics Used higher frequencies so less interference
Has high bandwidth thus faster transmission of data

17. Modem
Modems convert digital signals to analog and analog signals to digital
Modem is short for Modulate/Demodulate

18. Modem Speeds Modem speed is measured in bits per second
This is how many bits per second (bps) are being transmitted over the channel
Current speed for modems is 56.6 kbps

19. ISDN
ISDN (Integrated Services Digital Network) is designed to transmit a computer’s digital signal directly over a network
The entire network is digital

20. Benefits of ISDN No digital to analog conversion
Speed—data can be transmitted at 128,000bps much faster than modem
Voice and data transmission can happen at same time

21. Disadvantages of ISDN High initial costs On-going monthly fees
Possibly, a newer phone line is needed
Not available in some geographic areas
Newer technologies like DSL now becoming available

22. Microwave Transmission
Data is sent as signals through the atmosphere from one relay station to another
Line-of-sight transmission only

23. Microwave Transmission
Since signals cannot bend - needs relay stations (in high places) about 30 miles apart to continue transmission
Microwave transmissions are fast and cost-effective

24. Satellites
This form of communications link requires earth stations and transponders
Earth stations send and receive signals. Transponders amplify the signal, change the frequency, and retransmit the data to a receiving earth station

25. Satellite Transmission
Requires
Earth Stations - which send and receive signals
Transponders – receives the signal from an earth station, amplifies it, changes the frequency and sends it on to another earth station near the destination

26. Wireless Networks
Use radio waves and/or microwaves to maintain communication channels between computers
The data is beamed out over the airwaves
Advantages of wireless include mobility and elimination of unsightly cables

27. Advantages of Wireless
Users with personal digital assistant (PDA) handheld computers such as Palm Pilots or with laptops can use wireless technology to allow them to move about while maintaining their network connectivity

28. Advantages of Wireless
The ability for users to network desktop computers at various locations without the trouble or expense of wiring

29. Disadvantages of Wireless
Slower than wired networks
Equipment more expensive
Wireless networks are affected by obstructions such as walls etc in their vicinity
Interference from other wireless devices such as cell-phones
Interference from weather

30. Mix and Match
Most networks will be a combination of the many technologies that have been looked at here