Module 7 Part 1Module 7 Part 1

Introduction To NetworkingIntroduction To Networking

2

ObjectivesObjectives

• Understand the history of data communications• Describe the basic components of a network• Explain the methods of data transmission,

including types of signals, modulation, and choices among transmission modes

• Differentiate among the various kinds of communications links and appreciate the need for protocols

3

Data Communications SystemsData Communications Systems

• Computer systems that transmit data over communications lines such as telephone lines or cables

• History– Centralized data processing in early days– Distributed data processing began in late

1960s– Networks of personal computers began in

1980s

4

Centralized Data ProcessingCentralized Data Processing

• Places all hardware, software, and processing in one location

• Very inconvenient and inefficient– Input data had to be physically transported to

computer– Processed material had to be delivered to

users

5

Distributed Data ProcessingDistributed Data Processing

• Uses computers that are at a distance from central computer

• Local computers had access to central computers– Some processing done on local computers,

some on central computers

6

NetworkNetwork

• A group of two or more computer system that are linked together to exchange data and share resources over communication lines

• Uses communications equipment to connect two or more computers and resources– Distributed data processing systems are

networks – Local area network (LAN) designed to share data

and resources among several users in office or building

7

Putting Together a NetworkPutting Together a Network

• Basic Components– Sending device– Communications link– Receiving device

modems

routers

switches

(NIC) Network Interface Cards

computers

8

Network FundamentalsNetwork Fundamentals

• Node – Any workstation or peripheral that is connected to

network server, computer, peripheral devices, such as printer

• Network Interface Card(NIC) – expansion boards that fit into a computer’s expansion

slot. – Provide electronic connection between a computer

and the network.

9

• Routers – Can determine the best path to route data– If traffic is clogged on one path, the router will

determine an alternative path

• Switches– Perform same function as router– However, it is simpler and faster

mechanism than a router

Network FundamentalsNetwork Fundamentals

10

Digital and Analog TransmissionDigital and Analog Transmission

• Digital transmission

• Analog transmission

• Modem

11

Digital TransmissionDigital Transmission

• Sends data as distinct pulses, either on or off– Similar to how data travels through computer

12

Analog TransmissionAnalog Transmission

• Continuous electrical signal in the form of a wave– Called carrier wave

• Many communications media already in place for analog (voice) transmission– Phone lines are most common

• Digital signal from computer must be converted to analog form to be transmitted over analog lines

13

Converting Digital to AnalogConverting Digital to Analog

• Carrier wave can be altered– Amplitude (height) of wave– Frequency (number of times a wave repeats

during a cycle) of wave

• Conversion from digital to analog called modulation

• Conversion from analog to digital called demodulation

14

Converting Digital to AnalogConverting Digital to Analog

analog signalContinuous electrical

wave

digital signalDistinct pulses that

represent bits grouped together into bytes

15

ModemModem

• Short for modulator/demodulator

• Converts digital signal to analog and vice versa– Modulate convert from

digital to analog– Demodulate convert

from analog to digital– Speeds up to 56,000 bps

(56K)

Internal modem -resides on an expansion board that plugs into a computer

ADSL modem

PC Card modem

16

Types of ModemsTypes of Modems

• External modem separate from computer

• Internal modem inserted into computer– Standard on most computers today

• PC Card modem slides into slot on laptop– Roughly credit card size

• Cable connects modem to standard phone jack

17

Modem Data SpeedsModem Data Speeds

• Measured in bits per second (bps)– Early modems transmitted at 300 bps– Fastest current modems transmit at 56,000

bps

• Federal Communications Commission (FCC) restrictions prohibit actual speeds faster than 53,000 bps

• Actual speed depends on line conditions and other variables

18

Other Communications DevicesOther Communications Devices

• ISDN

• DSL

• Cable modems

• Cellular modems

19

Integrated Systems Digital Network (ISDN)

Integrated Systems Digital Network (ISDN)

• Special type of telephone circuit– Can move data at 128,000 bps– Includes two phone lines, so you can talk on

the phone while online

• Drawbacks– Expensive, especially at installation– Not available in all areas

20

Digital Subscriber Line (DSL)Digital Subscriber Line (DSL)

Advantages of DSL: • Can leave your Internet connection open and

still use the phone line for voice calls. • The speed is much higher than a regular modem • DSL doesn't necessarily require new wiring; it

can use the phone line you already have. • The company that offers DSL will usually provide

the modem as part of the installation.

21

Digital Subscriber Line (DSL)Digital Subscriber Line (DSL)

Drawbacks• A DSL connection works better when you are

closer to the provider's central office. • The connection is faster for receiving data than it

is for sending data over the Internet.

• The service is not available everywhere.

22

Cable ModemsCable Modems

• Uses coaxial cable already in place for your TV– Very fast transmission speed, especially for

downloading– Always on: no need to dial a connection

• Drawbacks– All users share a cable segment’s capacity

• As more users in neighborhood go online, speed decreases

– No security for individual users or data• Purchase a firewall program for security

23

Cellular ModemsCellular Modems

• Transmit data over the cellular telephone system– Roughly half the speed of a regular telephone

network

24

Data TransmissionData Transmission

• Simplex sends data in one direction only– Example: television broadcasting

• Half-duplex sends data in both directions, but only one way at a time– Example: bank teller sends data about a deposit; after

data received, a confirmation returns

• Full-duplex allows transmission in both directions at same time– Example: a conversation– Typically used for high-speed data communication

25

Communications MediaCommunications Media

• Physical means of data transmission• Bandwidth is measure of the capacity of the

communications link– Speed at which a line carries data and information– The faster the transfer rate, the faster you can send

and receive data and information– Usually expressed as a measure of bits per second

bits per second (bps)

kilobits per second (Kbps)

megabits per second (Mbps)

gigabits per second (Gbps)

26

Types of Communications MediaTypes of Communications Media

• Wire pairs• Coaxial cables• Fiber optics• Microwave

transmission• Satellite

transmission• Wireless

transmission

27

Wire PairsWire Pairs

• Also known as twisted pair– Two wires twisted around

each other to reduce electrical interference

• Inexpensive• Already in place (for

telephone systems)• Susceptible to electrical

interference and noise – Noise - anything that causes

signal distortion

28

Coaxial CableCoaxial Cable

• A center conductor wire surrounded by layer of insulation and metallic sheath

• Commonly used to connect to cable TV• Higher bandwidth and less susceptibility to noise than

twisted pair

29

Fiber OpticsFiber Optics

• Use light instead of electricity to send data• Much higher bandwidth than coaxial cable• Immune to electrical interference• Materials cheaper than coaxial, but installation costs

high

30

Microwave TransmissionMicrowave Transmission

• Uses line-of-sight transmission of data signals– Sending microwave

must “see” receiver• Requires relay

stations approximately every 30 miles– Waves are straight,

earth is curved• Offers high speed

and cost-effectiveness

• Susceptible to weather conditions

31

Satellite TransmissionSatellite Transmission

• A form of microwave transmission– Satellite acts as relay

station• Components

– Earth station sends and receives signal to satellite

– Transponder receives and amplifies signal, changes frequency, and retransmits data

• Useful when signal must travel thousands of miles

32

Wireless TransmissionWireless Transmission

• Transmits data over relatively short distances without wires

• Examples– IrDA - uses infrared line-of-

sight– Bluetooth - uses radio waves

to connect mobile devices– 802.11 standards - govern

wireless transmission

33

Setting StandardsSetting Standards

• Protocol - a set of rules for the exchange of data between a terminal and a computer or two computers– Agreement on how data is to be sent and

receipt acknowledged– Needed to allow computers from different

vendors to communicate– Transmission Control Protocol/Internet

Protocol (TCP/IP) permits any computer to communicate with the Internet