An elementary telephone system consists of two elements:
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For each subscriber, the system must contain the equipment necessary to convert sound to electrical signals and back. This equipment is called the "telephone" and allows users to speak and hear each other. Most telephones are in two parts: The handset is a handle containing the transmitter and receiver. The base contains a dial to initiate a call and a bell or other signaling device to notify the user of a telephone call from another user. Some telephones have more or fewer parts, and some don't have this kind of integrated handset.
- The system must connect the two or more telephones together. Historically, and still usually, this is by means of twisted pair wire, and usually via the worldwide telephone network or PSTN.
Facts
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Land line phones are usually cheaper to use than mobiles.
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Most models allow you to store the numbers you use a lot.
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They can be connected up within a building so that internal phone calls are free.
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Some phones have video screens
Mobile phones
Mobile phones are actually sophisticated radios.
Service providers erect radio masts to broadcast signals.
You can contact a person without knowing where they are.
Phones store numbers for your contacts.
Some have extra features such as calculators, cameras and diaries.
Some allow the user to connect to the Internet to check e-mail and view WAP sites.
Instant messaging
Instant messaging (IM) allows you to set up a list of people online you want to “talk” to.
Each user types their message, and the other person can see it straight away.
IM lets you exchange files, and you know the other person has received them.
You can send hyperlinks to web sites.
You can also talk using a microphone or a web cam.
IM is cheaper than long distance phone calls.
Video conferencing
Business meetings can be expensive, especially if people have to travel to get to them.
Video conferencing links two or more computers so that they can stream live video and sound.
Cameras and microphones capture the data and send it across the communications network to monitors and speakers.
The people in the meeting can see and hear each other, as they would if they were in the same room.lll
They can send files to each other if they need to share documents.
Text messaging
Text messaging is also called SMS (short message service).
SMS is usually used on mobile phones.
The user types their message, and sends it to the other person’s mobile phone.
They open the message when they next switch on their phone.
Messages are cheaper than mobile phone calls.
Phones can also send picture messages and video.
Fax
Fax is short for facsimile – a picture of something rather than the real thing.
The fax machine scans a document and sends a black and white picture of it to the receiver. They then print out a copy of the document when it is transmitted.
You can only fax to one person at a time, and you pay international rates to send abroad. The document loses some quality as you transmit it.
E-mail
E-mail (electronic mail) sends messages between computers.
The sender writes the message and presses send.
The message is then sent to the other person’s e-mail server.
They download it next time they log on.
You can attach files to e-mails for the other person to open and use.
You can send e-mail to groups of people at the same time.
