COMMUNICATION DEVICES AND MEDIA By the end of this unit

1
Communication devices and media

• By the end of this unit students should be able
  to
• Distinguish between communication devices and
  communication media.

2

• Efficient data communication must be
• Accurate
• Timely
• Cost effective
• Data communication allows users to transmit and
  receive data and information. This information
  is used to identify and solve problems and to
  make informed choices.

3
Terms

• Media a collective name for materials (tape,
  paper, disk, etc) used to transmit data.
• Communication media the material used to
  transmit data and includes cables, fibre-optic
  cables, radio waves and satellite links.

4

• Communication Devices the parts of the computer
  that facilitate communication by using the above
  media.
• Modem the most commonly used computer
  communication device.
• Other communication devices include local area
  network cards (LAN), network hubs, and wireless
  cards.
• Telecommunications is the sending and receiving
  of data by means of cable or wireless devices and
  media.

5

• Interface a device that allows otherwise
  incompatible items to be connected.
• It is sometimes an external device with its own
  power supply that is plugged into the computer.
  Eg. Modems, network cards and wireless cards.

6
MODEMS

• They use the already-existing telephone network
  to facilitate computer communication.
• Telephone lines were designed to communicate the
  human voice, so they transmit data using sound
  waves or what is called an analogue data form.
• Before computer signals can be sent via telephone
  lines they must be converted from digital to an
  analogue format. This process is called
  MODULATION. For more information click here.

7

• When the signal reaches the receiving computer it
  is converted back from analogue to digital form.
  A process called DEMODULATION.
• Modems are usually used to connect a computer to
  the Internet and to send and receive faxes via
  the computer.
• Modems constantly check whether the information
  was received properly or not.
• The information is broken down and sent in groups
  called PACKETS. Each packet is checked for
  errors and is re-sent if there is an error.
• Click on the link below to see how the modem
  works.

http//tdi.uregina.ca/flash/cs100/modem-general.h
tml
8
Digital phone lines

• Advantages
• There is no need to use a modem when using a
  digital telephone line such as an ISDN
  (integrated services digital network) line to
  connect a computer (or a LAN) to the Internet
  because the signal is already a digital one which
  a computer can process.
• A larger volume of data is transmitted more
  quickly.
• ISDN line is used for voice, video, and data
  transmission. Users can receiving telephone
  calls, transmitting faxes and surfing the
  internet at the same time using the same line.

9
Facsimile or fax machine

• This scans a document with a beam of light and
  converts the image to a coded series of signals
  that can be transmitted along telephone lines.
• The receiving machine interprets the coded
  signals and prints out a copy of the document.
  It is an exact representation of the text,
  photographs and graphic images in the original
  document.
• Some computers are equipped with fax modem so
  that you can transmit a typed document directly
  from the senders computer to the recipients fax
  machine or computer.

10
networks

• LOCAL AREA NETWORKS (LAN)
• WIDE AREA NETWORKS (WAN)
• WIRELESS NETWORKS (WN)
• CELLULAR NETWORKS (CN)

11
LOCAL AREA NETWORK (LAN)

• A network is a set of computers and peripherals
  that are linked together so that they can
  communicate with each other and share resources.
• If the computers are joined by cables in a small
  area such as a room or building, it is called a
  LOCAL AREA NETWORK (LAN).
• All the computers are less than a kilometer away
  from each other.
• In a lab several computers may be linked in order
  to share a printer. One computer may be the
  server, which controls and provides services for
  the LAN. The printer is connected to the server
  but can be accessed by all the other computers.

12
Types of lans
13

• A network card is a small circuit inside the
  computer. It allows the computer to communicate
  with others that are on the network.
• A cable is plugged into the card and each
  computer then has access to any shared programs,
  devices and files on other computers or a main
  server computer.
• Each network card has a unique address to make
  sure the correct data is delivered to it.
• Some use cables or wireless.
• The cables used may be twisted pair, coaxial or
  fibre- optics.

14

• Twisted pair cheapest but relatively slow, used
  where a rather small volume of data is
  transmitted or where speed is not important.
• Coaxial cable faster, more expensive, used
  where large amounts of data are being
  communicated eg. Voice and video transmission.
• Fibre-optics fastest and most expensive.
  Transmit data as digital pulses of light. They
  are not affected by electromagnetic interference
  and transmit data over large distances. Transmit
  large volumes of data quickly and accurately.

15
Wide area networks (WAN)

• When computers which are located in different
  locations are linked using telephone lines or
  satellite, a WAN is formed.
• They cover large areas such as a city, a nation
  or the entire world.

16
Wireless networks

• Both LANS and WANs may be created using wireless
  technology.
• As the name suggests there are no wires.
• It uses infrared or microwave radio signals to
  transmit and receive data. Wireless networks are
  use where cables are inconvenient, e.g if the
  network is created among buildings separated by
  streets.
• They are usually more expensive than cable-linked
  networks.
• More readily used now as costs declines.

17
Cellular networks

• Mobile telephones are now regularly used to
  communicate while travelling or away from home.
• Some cellular phones offer facilities for
  browsing the internet and sending and receiving
  faxes and electronic mail.

18
How the cellular network works

• It is created when transmitters are place in a
  checkerboard pattern throughout a service area.
• The geographical area that is served by a
  transmitter is called a CELL. Unique frequencies
  are assigned to each cell.
• Each cell phone transmits and receives a signal.
  When you place a call, the cell in which the
  caller is located detects the signal from your
  cell phone.
• The cell then assigns a specific frequency to
  that call and the call is transmitted to the
  receiving unit.

19

• A computer system monitors the strength of the
  signal from the cell phone.
• As you move away from the transmitter, the signal
  weakens.
• If the signal falls to a preset level, the
  computer recognizes that you have left the cell
  and scans the surrounding cells to determine the
  new area into which you have moved.
• The transmitter in the new cell takes over the
  call and a new frequency is assigned to your
  phone.
• This happens so quickly that you do not detect
  the transfer. If you move too far away from any
  network transmitter, the connection breaks.

20
The internet

• The worlds largest network. It is a worldwide
  collection of networks that links together
  millions of computers by means of modems,
  telephone lines and other communication devices
  and media.
• It is used by more that 100 million people.
• It can be accessed either through a file server
  or through an Internet service provider (ISP) or
  online service.
• A file server is a computer that is permanently
  connected to the Internet.

21

• File servers are used by large organisations.
• An ISP is an organisation that supplies
  connections to the Internet for a monthly fee.
• An online service provides access to the Internet
  but also provides other services such as
  financial information, entertainment, hardware
  and software guides, news and weather, and direct
  messaging.
• Fees for online service are usually higher than
  for an ISP.
• The internet enables users to send and receive
  mail electronically.
• Electronic mail (email) is so quick that
  traditional mail is now called snail mail.

22

• Direct messaging enables users to meet and
  communicate with persons all around the world
  using either typed or voice messages.
• The internet enables employees with PCs to
  connect to the organisations mainframe or
  supercomputer without travelling to these
  locations. It has also made Ecommerce possible.
• Discussions boards allow participants to type
  messages about a given topic. Responses are
  usually linked to each other to allow the reader
  to easily follow the discussion.

23
Intranet and extranet

• Intranet private network of computers with an
  organisation that provides functions similar to
  the public internet.
• These functions include email and newsgroups
• They do not allow access via the internet and has
  security features to prevent unauthorised access.
• Extranet an internal company network that has a
  connection to the public internet and allows
  users to gain access via the internet. It
  provides access to people in the organisation who
  are working away from the office.
• Web page a file that is saved on the computer
  on the internet.
• Web site a collection of web pages.

24
teleconferencing

• This makes use of telecommunications technology
  to allow participants in two or more locations to
  speak with each other.
• It is a group conference call in which all
  participants are able to speak with each other.
• Online meetings allow computer users to access
  the Internet to create a chat room in which they
  can exchange typed messages instantaneously.
• Video conferencing allows users in distant
  locations to see each other.

25
QUESTION TIME

• See how much you can remember
• Click here to see the questions.

26
bibliography

• Electronic Document Preparation and Management
  for CSEC
• by Ann Margaret Jacob and Agatha Augustine
• http//www.webopedia.com/TERM/m/modem.html