Introductory Communications Objectives  To gain an overview of: Modems and digital telephone lines Analogue to digital conversion and digital to analogue conversion Advantages and disadvantages of using computer networks User ids and passwords Communication 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 digital analogue 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are known as Integrated Services Digital Network Lines, or ISDN Can handle large amounts of data These are now being superseded by…

ADSL Skinny Voice - Broad Band! A symmetric D igital S ubscriber L ine 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 ( ) A message sent electronically from one person to another using “computers” connected to a network To send an 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 address

Electronic 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  Long files including video, sound and graphics can be sent.  It is easy to send a reply to an as soon as it is received or forward it to someone else. has many advantages over both ordinary mail and the telephone. For example:

Voic 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