Introductory Communications

ObjectivesTo gain an overview of:

Modems and digital telephone linesAnalogue to digital conversion and digital to analogue conversionAdvantages and disadvantages of using computer networksUser ids and passwordsCommunication media

Communication Links

Sometimes it may be necessary for an individual computer to exchange information with another computer.

To do this they have to be connected in some way.

Computers that are linked can communicate with one another over long distances

Messages need to be sent in a digital format

Standard Telephone Lines

Old technology (designed over 100 years ago!)

Designed for carrying sound in analogue form

To transmit Data over a standard phone line, the data must be converted from a digital to an analogue signal

How?

The word "modem" is a contraction of the words MO-dulator & DEM-odulator

The sending modem modulates (Converts) the data into an Analogue signal that is compatible with the phone line, and the receiving modem demodulates (Converts) the signal back into digital data.

modem modemdigital digitalanalogue

Modem

Digital Communication Lines

Especially designed to transmit these messages

They are known as Integrated Services Digital Network Lines, or ISDN

Can handle large amounts of data These are now being superseded by…

ADSLSkinny Voice - Broad Band!

Asymmetric Digital Subscriber Line Copper phone lines can carry much more than your

phone call.

They can handle a much greater Bandwidth, (or frequency range) than is needed for voice.

Voice transmission over a phone line is carried on a bandwidth between 0 - 3,400 Hertz.

The phone lines can have the potential to handle frequencies up to several million Hertz!

Digital Subscriber Lines make use of this spare capacity.

ADSL Modems Skinny Voice - Broad Band!

Other types of Comm Link

Satellite Microwave Radio Waves Wireless communication links that

operate without the use of cables are becoming more popular.

Computer Networks

A network of computers is when several computers have communication lines linking them.

Many types of network One type is when many computers are linked so

that data can be sent from one to another. Another type has many computers connected to

a main computer called a Network Server.

Computer Networks

Used to allow users to share data & software

Examples: Banks Supermarkets Internet?

Computer Networks

Advantages Programs & Data can be shared Possible for all users to communicate

with each other Share resources like a printer

Computer Networks

Disadvantages High installation cost Security issues Specially trained staff needed to maintain

network If network fails you may not be able to

access your work If lots of people log on together the

network may run slowly.

User ID’s & Passwords

Important that we can only see data which belongs to us.

Others should not have access to our data

User ID tells the network what you can have access to

Password attempts to ensure that you are who you say you are.

User ID’s & Passwords

To keep your work safe and secure it is important to: Keep your password private Change your password frequently Log off the network properly

More Ways of Communicating

Fax Scans and digitises images (text or graphics) Transmits them in analogue form over a telephone

line to another fax machine, which then produces a copy of the image on a piece of paper

Indispensable to even the smallest business Greatly speeds up business transactions

Advantage of Fax

Send documents e.g. orders, newspaper cuttings, maps, instantly

Written evidence with signature No need for recipient to be there,

unlike phone For example, can book a car / hotel

in Australia with ease and get immediate confirmation

Disadvantage of Fax

Paper jam Runs out of paper / ribbon (when you’re

away) Attracts junk faxes Insecure - others can read your

“confidential” fax on the machine before you get there

Electronic mail (E-mail)

A message sent electronically from one person to another using “computers” connected to a network

To send an email you need: A computer processor A communication link Software to enable you to read, write, send &

retrieve messages An agreement with a service provider An e-mail address

Electronic mail (E-mail)

A message can be sent from your desk to anywhere in the world.

The same message can be sent simultaneously to a group of people.

The message should arrive instantly, and can be picked up the next time the recipient looks at their e-mail

Long files including video, sound and graphics can be sent. It is easy to send a reply to an e-mail as soon as it is

received or forward it to someone else.

E-mail has many advantages over both ordinary mail and the telephone. For example:

Voicemail

A sophisticated answering machine Various services or departments available when you press a

particular key Messages can be directed to individuals who are absent Messages can be cleared or forwarded

Advantages Fast routing or caller to service Ability to leave messages

Disadvantages Can be impersonal Can be frustrating (Press 1 for this 2 for that…blaa blaa blaa)

Teleconferencing

Allows people in different locations to exchange ideas and information interactively

Most basic form Telephone

More advanced – videoconferencing Video cameras Microphones Large monitors Computers Usually a dedicated room is required – adding to the cost

MSN Messenger Latest version could replace expensive VC equipment Only needs web cam & microphone to be added to a PC

But…High-bandwidth required (at least ISDN) for credible VC Bandwidth is a measure of how much data can be passed down a line