Network Concepts and Communications

8/10/2019 Network Concepts and Communications

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Network Concepts and

Communications


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Network Concepts

and Communication

In this chapter:

What can be done online?

How are computers connected? What are the physical properties of networks?

How does a computer know how to

communicate with a network?

Can all computers talk to each other?


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Introduction: Everything is

Connected to Everything

Going online: Connecting to a collection of

interconnected computers on a network. Do banking.

Pay bills. Buy groceries.

Book vacation travel.

Send messages.

Participate in discussions. Do research.

Play games.


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Introduction: Everything is

Connected to Everything

Network: A collection of computers, display terminals,

printers, and other devices linked either by physical or

wireless means.

Seeds of Networking 1966: ARPA (Advanced Research Projects Agency)

State Defense Departments research organization.

Focused major development effort on computer networking.

ARPAs Goal: To promote research in advanced future

technologies by funding university and industry research

proposals.

Result: Thousands of databases became available to the

public.


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Client Server Network

Division of labour client program handles user interface and

light processing chores

server program handles heavy work, likedatabase retrieval, and accessing centralised

resources

Client Machine Server

Client ProgramServer

Program


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Computer 1

Computer 3Computer 4

Computer 2

Server

Printer


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The Internet: A Network of

NetworksComputer Networking

Internet: A world-wide networkconnecting millions of computer networks

for the purpose of exchanging data andcommunications using special rules ofcommunication.

The Internetis an interconnected network

of thousands of networks linking academic,research, government, and commercialinstitutions.


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Communication Basics

of Networks

Types of connections of computers intonetworks: Physical versus Wirelessconnections

The first type: The Physical Connection.Physically connect computers together.

Use of wires or optical cables.

The connections are called network links.

Three most common physical links:Twisted pair

Coaxial cable

Fiber-optic cable


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of Networks

Twisted pair

Two wires twisted together.

A physical communications channel that uses

strands of copper wire twisted together in pairs,acting like an antenna and picking up radio

frequency information or appliance noise.

Telephone company uses twisted-pair copper

wires to link telephones.


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of Networks

Coaxial cable

Also two wires:

One of the wires is woven of fine strands of copper

forming a tube. The wire mesh surrounds a solid copper wire that

runs down the center.

Space between has a non-conducting material.

Makes them more impervious to outside noise.


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of Networks

Fiber-optic cable

Light is electromagnetic.

Can transmit more information

down a single strand. It can send a wider set of

frequencies.

Each cable can send several

thousand phone conversations

or computer communications.


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of Networks

Second type of connections of computersinto networks: Wireless connections

The link is made using electromagnetic

energy that goes through space instead ofalong wires or cables.

Three types of wireless communicationscommonly used in networking:

InfraredRadio frequency

Microwave


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of Networks

Infrared

Commonly used in TV and

VCR remote controls.

Use infrared frequencies ofelectromagnetic radiation that

behave much like visible light.

Must be in the line of sight.

Often used to connectkeyboards, mice,

and printers.


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of Networks

Radio frequency

Uses radio frequencies.

Function even though line of sight is interrupted.

Not commonly used because of the possibleinterference from other sources of

electromagnetic radiation such as old electric

drills and furnace motors.


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Microwave Often used to

communicate withdistant locations.

Must be line of sight.

Satellitecommunications usemicrowaves.


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of NetworksProperties of Transmission

Five basic properties of both the physical and wirelesslinks:

1. Type of signal communicated (analog or digital).

2. The speed at which the signal is transmitted (howfast the data travels).

3. The type of data movement allowed on the channel(one-way, two-way taking turns, two-waysimultaneously).

4. The method used to transport the data(asynchronous or synchronous transmission).

5. Single channel (baseband) and multichannel(broadband) transmission.


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of Networks

Type of signal communicated (analog ordigital).

Analog:Those signals that vary with smooth

continuous changes.A continuously changing signal similar to that

found on the speaker wires of a high-fidelity stereosystem.

Digital: Those signals that vary in steps orjumps from value to value. They are usually inthe form of pulses of electrical energy(represent 0s or 1s).


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of Networks

The speed at which the signal is transmitted(how fast the data travels).

In digital systems: Speed is measured in...

Bits per second(bps).

The number of bits (0s and 1s) that travel

down the channel per second.


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Need for Modem

The computer

communicates

with digital signals

The telephone system

was designed to transmitvoice signals which are

analog


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of Networks

MODEM- MOdulatorDEModulator

Outgoing: Converts binary data

from computer (digital) intotelephone compatible signals(analog).

Incoming: Converts telephone

signal (analog) into binary datafor the computer (digital).

Can be an external or internaldevice (usually a card).


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of Networks

The type of data movement allowed on thechannel.

Simplex transmission - One way transmission.

Half-duplextransmission - Flows only one

way at a time.

Full-duplextransmission - Two-way

transmission at the same time.


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The method used to transport the data.

Two types of data transmission, each requiring

a different modem.

Asynchronous transmission-

Information is sent byte by byte.

Cheaper and more commonly used.

Synchronous transmission-

Data is sent in large blocks rather than in smallpieces.

Preceded by special information, concerning error

detection and block size.

These modems are expensive but very fast.


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of Networks

Single channel versus multichanneltransmission

Channel- A path of a signal.

Single channel- Capable of onlysending/receiving one signal at a time.

Phone line: Single line = single phone call at a

time.

Multichannel - Capable of more than onechannel at a time.

Fiber-optic cable, microwaves, Satellite

transmissions.

C i ti B i


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of Networks

How is it possible to measure the capacity

of communications links? Bandwidth: DigitalNumber of bits per second (bps) that can be sent

over a link.

The wider the bandwidth, the more diverse kinds of

information can be sent.Simplest is voice, most sophisticated is moving

videos.

Bandwidth: Analog The difference between the highest and lowest

frequencies that can be sent over an analog link(like phone lines).

Measurement is given in hertz (Hz).

For both:The wider the bandwidth, the moreinformation can flow over the channel.


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Typical cable bandwidths used in local area networks.

Cable: Typical Bandwidth:Twisted Pair 10 to 100 Mbps

Coaxial Cable 10 to 100 Mbps

Fiber-optic cable 100 to 200 Mbps


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The Physical Organization

of Networks

Two parts to connect computers to networks

The hardware needed to connect the

computer to the network.

The software needed to control the hardware.

(Software standards will be discussed in the next

section.)


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of Networks

Node: The generic name given to all deviceshooked up to a network.

Each node must have a unique address assigned to

them by the network.

Networks are either direct-connected or those that arenot directly linked.

Direct-connected network: Those whose nodes have

direct connections through either physical or wireless

links. Point-to-point: Simplest version of direct-connected

network. Connecting two computing systems.

Example of point to point: Home to ISP.

Example of a network that is not directly linked: Internet.


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of Networks

The bus network- A continuous coaxial cable to

which all the devices areattached.

All nodes can detect all

messages sent along the bus.

The ring network- Nodes linked together to form a

circle.

A message sent out from onenode is passed along to eachnode in between until the targetnode receives the message.

Linking nodes:

Th Ph i l O i ti


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of Networks

The star network- Each node is linked to a

central node.

All messages are routed

through the central node,who delivers it to the

proper node.

Linking nodes:


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of Networks

The fully connected network

-

All nodes are connected to all

other nodes.

Internetworking -

Connecting together any numberof direct-connected networks.

The largest: Internet.

Linking nodes:


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of Networks

There are two general types of computer

networks:

LAN

(Local Area

Network)

WAN

(Wide Area Network)


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of Networks

LAN(Local Area Network)A collection of nodes within a small area.

The nodes are linked in a bus, ring, star, tree,or fully connected topology network

configuration.

Benefits of LANs:Sharing of hardware resources.

Sharing of software and data.Consolidated wiring/cabling.

Simultaneous distribution of information.

More efficient person-to-person communication.


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MAN(Metropolitan Area Network) Consists of many local area networks linked

together.

Span the distance of just a few miles.

WAN(Wide Area Network)

Consists of a number of computer networks includingLANs.

Connected by many types of links.


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Internet Connections

There are many types of Internet

connections

1) DIALUP

2) DSL

3) VSAT

4) ISDN5) DEDICATED LINE


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DIALUP

This is the most basic type of Internet

connection.

This connection is made through a

modem, that uses a telephone line to

connect to the Internet.

The modem must dial the telephone every

time it wants to connect to the Internet,hence the name dial-up connection.


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DSL (Digital Subscriber Line )

An DSL connection uses high-speed transmissions

through telephone lines.

DSL connections are speedy

The only caveat here is that the closer you are to the

main telephone switching station, the faster yourconnection speed will be.

There are two types of DSL such as ADSL and SDSL.

There are two types of DSL internet connection,

namely Asymmetrical Digital Subscriber Line (ADSL)

and Symmetrical Digital Subscriber Line (SDSL). The

difference between the two is their data transfer

speed.


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ISDN

An ISDN (Integrated Services Digital Network)

connection uses high-speed, high-quality digital

telecommunication lines.

The advantage of an ISDN service is that theyare made up of digital circuits.

This special phone line must be installed by a

phone company

ISDN supports data transfer rates of 64 Kbps


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VSAT

VSAT (Very Small Aperture Terminal) is a

satellitecommunications system

A VSAT consists of two parts, a transceiverthat

is placed outdoors in direct line of sight to thesatellite and a device that is placed indoors to

interface the transceiver with the end user's

communications device, such as a PC

VSAT handles transmission rates of up to 56

kilobits per second.
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Working of VSAT

The tranceiver receives or sends a signal to asatellite transponderin the sky. The satellitesends and receives signals from an earth stationcomputer that acts as a hubfor the system.

Each end user is interconnected with the hubstation via the satellite in a star topology. Forone end user to communicate with another,each transmission has to first go to the hub

station which retransmits it via the satellite to theother end user's VSAT.

VSAT handles data, voice, and video signals.
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DEDICATED LINE

A telecommunications line that lets your

computer have a direct, permanent

connection to the Internet; in contrast with

a dial-up connection which is only openedfor temporary use.

is not shared in common among multiple

users as dial-up lines are


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Wi Fi stands for Wireless Fidelity and is

used to define any of the wireless

technology

the most common usage of Wi Fi

technology is for laptop users to gain

Internet access in locations such as

airports, coffee shops


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Internet Service Providers (ISPs)

An Internet service provider (ISP) is anorganization that provides Internet accounts,

whether dial-in, DSL, ISDN, cable, satellite, or

wireless. Thousands of ISPs exist in the United States, including dozens of ISPs with

dial-up access phone numbers throughout

the country, and many with phone numbers in

limited regions. For example, EarthLink (www.earthlink.com) has access phone

numbers in all major U.S. cities, whereas


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Intranet

An Intranet is a network based on the internet

TCP/IP open standard. An intranet belongs to an organization, and is

designed to be accessible only by theorganization's members, employees, or others

with authorization. An intranet's Web site looks and act just like

other Web sites, but has a firewall surrounding itto fend off unauthorized users.

Intranets are used to share information. Secureintranets are much less expensive to build andmanage than private, proprietary-standardnetworks.

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Network Concepts and Communications