Lecture 5 Communications and Networks .

Lecture 5

Communications and Networks

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Communications

What is computer communications? A process in which one computer transfers data,

instructions, and information to another computer(s)

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Uses of Communications Technologies Voice mail

Fax E-mail Chatroom Instant Message FTP

Newsgroup Telephony Videoconference Groupware Global Positioning

System (GPS)

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share software

share hardware

Networks

What is a network? A collection of

computers and devices connected by communications channels

Facilitates communications among users

Allows users to share resources

facilitate communications

share data and information

Networks

What is a local area network (LAN)?

Network that connects computers and devices in a limited geographical area.

Often uses Ethernet protocol

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Networks

What is a node ? Each computer or device on a network

often the nodes are connected to the LAN via cables

a wireless LAN (WLAN) is a LAN

that uses no physical wires

node

node

node

node

node

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Administration

Adding, deleting, and organizing users and performing maintenance tasks

File management

Locating and transferring files

Networks

What is a network operating system? The system

software that organizes and coordinates the activities on LAN

Also called a network OS or NOS Printer management

Prioritizing print jobs and reports sent to specific printers on the network

Security

Monitoring and, when necessary, restricting access to network resources

Networks

What are servers and clients? Server• Controls access to the

hardware and software on the network

• Provides a centralized storage are for programs

• Dedicated servers perform a specific task

Clients• Other computers on the

network• Rely on the server for

resources

database server stores and provides access to a database

network servermanages network traffic

print server manages printers and print jobs

file server stores and manages files

Networks

What is an Internet use of peer-to-peer (P2P)?

An Internet network that enables users with the same networking software to connect to each other’s hard disks and exchange files directly

Napster and Gnutella are two examples of P2P

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Networks

What is a network topology? The configuration, or physical arrangement, of the

devices in a communications network Networks usually use combinations of three topologies

ring

star

bus

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Networks

What is a bus network? Consists of a single

central cable, to which all computers and other devices connect

The bus is the physical cable

The bus is also called the backbone

Inexpensive and easy to install

personal computer

personal computer

personal computer

personal computer

personal computer

Networks

What is a ring network? A cable forms a

closed ring, or loop, with all computers and devices arranged along the ring

Data travels from device to device around the entire ring

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Networks

What is a star network? All of the devices

connect to a central computer/hub

All data that transfers from one computer to another passes through the hub

host computer

printerfile server

personal computer

personal computer

personal computer

personal computer

Networks

uses TCP/IP technologies

has a Web server

supports multimedia Web pages coded in

HTML

accessible via a Web browser

users can post and update information on the intranet by creating and posting a

Web page

An internal network that uses Internet technologies

Generally make company information accessible to employees and facilitate working in groups

Typically also includes a connection to the Internet

What is an intranet?

Networks

What is an extranet? Allows customers

or suppliers to access part of a company’s intranet

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Networks

What is a firewall? Hardware and/or software that restricts access to data

and information on a network

personal computer

personal computer

personal computer

personal computer

personal computer

personal computer

personal computer

printer

firewall

corporate network Internet

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Networks

What is a home network? Multiple computers connected together

in a home or home office All computers in the

house can• connect to the

Internet at the same time

• Access files and programs on the other computers in the home

• Share peripherals

Networks

What is an intelligent home network? Extends the

basic home network to include features such as lighting control, thermostat adjustment, and a security system

Communications Software

What is communications software? Consists of programs that help you establish a

connection to another computer or network Manages the transmission of

data, instructions, and information

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The Telephone Network

What is a dial-up line? A temporary connection that uses one or more analog

telephone lines for communications A modem at the sending end dials the telephone

number of a modem at the receiving end

Advantages

Costs no more than making a regular call

Computers at any two locations can establish a

connection using modems and the

telephone network

Disadvantage

Cannot control the quality of the connection because the

telephone company’s switching office randomly

selects the line

The Telephone Network

What is a dedicated line? A connection that always is

established between two communications devices

The quality and consistency of the connection is better because dedicated lines provide a consistent connection

Can be analog or digital

Digital lines transfer data and information at faster rates than

analog lineswww.shahidrasul.com

bits per second (bps)

The Telephone Network

What is transfer rate? The speed with which a line carries data and information The faster the transfer rate the faster you can send and

receive data and information Usually are expressed as bits per second (bps)

kilobits per second (Kbps)

megabits per second (Mbps)

gigabits per second (Gbps)www.shahidrasul.com

The Telephone Network

What are popular types of digital dedicated lines? ISDN DSL T-carrier CATV ATM

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Communications Devices

What is a communications device? Any type of hardware capable of transmitting data,

instructions, and information between a sending device and a receiving device

Sometimes the device must convert the data, instructions, and information from analog to digital signals or vice versa

dial-up modems

ISDN and DSL modems

cable modems

network interface cards

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Communications Devices

What is a modem? A communications device that converts a computer's

digital signals to analog signals before they are transmitted over standard telephone lines

Sometimes called a dial-up modem

modulateTo change into

an analog signal

demodulateTo convert an

analog signal into a digital signal

mo + dem

DSL modem

Sends and receives digital data to a DSL line

Communications Devices

What is a digital modem? One that sends and receives data and information to

and from a digital telephone line such as ISDN or DSL

ISDN modem

Also called an ISDN adapter

Sends and receives digital data to an ISDN line

Communications Devices

What is a cable modem? A modem that sends and receives data over the cable

television (CATV) network Currently much

faster than a dial-up modem or ISDN

Usually attaches to a USB port or a port on a network interface card

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Communications Devices

What is a network interface card (NIC)? A card you insert into

an expansion slot of a personal computer or other device, enabling the device to connect to a network

NIC for desktop computer

NIC for notebook computer

Communications Channel

What is a BUS? The communications path between two devices

twisted pair cable

twisted pair cable twisted pair wire

Physical Transmission Media

What is twisted-pair cable? Consists of one or more twisted pair wires bundled together Each twisted pair

wire consists of two separate insulated copper wires

Twisted together to reduce noise

Noise is an electrical disturbance that can degrade communications

coaxial cable

plastic outer coating

woven or braided wire

insulating material

copper wire

Physical Transmission Media

What is coaxial cable? Consists of a single copper wire surrounded by at least

three layers Often called

coax Often used

for cable television wiring

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fiber-optic cable between floors of a building

cable contains many optical fibers

outer covering jacket

Physical Transmission Media

What is fiber-optic cable? Contains a core of dozens or hundreds of thin strands of

glass or plastic Uses light to transmit signals Each strand

is called an optical fiber

• Thin as a human hair

protective coating

glass cladding

optical fiber core

transmitter

sends the broadcast radio

signal

Wireless Transmission Media

What is broadcast radio? A wireless transmission medium that distributes

radio signals through the air over long distances such as between cities, regions, and countries and short distances such as within an office or home

Slower and more susceptible to noise than physical transmission media

receiver

accepts the broadcast radio signal

must have an antenna that is located in the range of

the signal

transceiver

both sends and receives signals from wireless

deviceswww.shahidrasul.com

Wireless Transmission Media

What is cellular radio? A form of broadcast radio that is used widely for mobile

communications, specifically wireless modems and cellular telephones

A cellular telephoneis a telephone device that uses radio signals to transmit voice and digital data messages

mobile telephone switching office

(MTSO)

cell

cell

cell

cell

calling party in auto

called party

public switched telephone network

base station (microwave

station)www.shahidrasul.com

Wireless Transmission Media

What is a microwave station? An earth-based

reflective dish that contains the equipment necessary for microwave communications

Microwaves are extremely high-speed signals

Line-of-sight towers• Must transmit in a

straight line

Wireless Transmission Media

What is a communications satellite? A space station that receives

microwave signals from an earth-based station, amplifies the signals, and broadcasts the signals back over a wide area to any number of earth-based stations

Transmission to a satellite is an uplink

Transmission from a satellite to an earth-based station is a downlink

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Wireless Transmission Media

What is infrared (IR)? A wireless transmission

media that sends signals using infrared light waves

Requires a line-of-sight transmission

Many computers and devices have an IrDA port that enables the transfer of data using infrared light rays

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