Data Communication is the transmission of data

from one location to the other in order to enable

communication between the locations. Data

communication is achieved through the use of

computers, transmission cables, satellite and

wireless technology and software.

The data is transmitted via data communication

channels. These channels are categorized

according to their BANDWIDTH (volume of

data that can be transmitted through the channel

each second). There are three categories of

channels. These are:

1. NARROW-BAND – data is transmitted

at a slow speed, e.g. telegraph

transmission. (just over 10 characters per

second)

2. VOICE-BAND – telephone lines are

utilized, allowing data to be transmitted at

rates up to 8,000 characters per second.

3. BROAD-BAND – broad-band uses

fibre-optic cables, microwave and

satellite transmission of data.

There are various types of communication systems

that vary according to the direction in which data can

be transmitted. These are:

1. SIMPLEX - data can only be transmitted in

one direction.

2. HALF-DUPLEX – data can be transmitted in

both directions, but not at the same time.

3. DUPLEX (FULL DUPLEX) – data can be

transmitted in both directions at the same time

and independent of each other.

Questions1. What is data transmission?

2. A communication system is made up of 3 main parts . What are these parts?

3. Describe 3 forms of data transmission.

4. For your answers to q3 give an example of each.

5. Wireless communication can occur in several ways. Which method is used by your laptop to the school’s QRC network; a car driver’s wireless headphone and his phone;

NETWORKS

A network is a group of computers

and peripheral devices that are

connected to each other by cables

or wireless electronics. Networks

reduce costs and increases

efficiency by allowing the sharing

of programs, data and peripheral

devices. In some cases there are

special computers called servers

that are dedicated to the managing

of particular resources.

LOCAL AREA NETWORKS (LAN)

A Local Area Network (LAN) is made up of two or more computers

connected to each other within the same geographical area but not

necessarily within the same building. LANs are usually used by

small or medium size businesses. LANs are usually connected

using twisted pair cables or coaxial cables.

LAN TOPOLOGIES

How computers on a network are connected together determines its

topology. The most common topologies for a LAN are:

1. LINE OR BUS

2. STAR

3. RING

LINE OR BUS TOPOLOGY

This is a single line or cable with nodes at different points. Information can be transmitted in either direction

from any PC to another. The problem here is that several stations may want to transmit down the same line

simultaneously and there has to be the same strategy for deciding who gets the line. Before a station begins to

transmit, it checks that the channels is not busy, if it is, it has to wait before transmission can begin. Once it

begins, transmission, it listens for other nodes also beginning transmission. If the transmitted message

collides with another, both stations abort and wait a random period of time before trying again.

ADVANTAGES

1. Extending the network is easy.

2. It requires less hardware to setup.

3. It is easy to configure.

4. New equipment can be added to it.

DISADVANTAGES

1. Any problems with the main cable may cause the whole network to malfunction.

2. Packets of data may collide, resulting in loss of information.

STAR TOPOLOGY

All the computers on the network are connected to one another through a central HUB. A HUB is a hardware device to which a

number of computers can be connected. Data is transmitted from one computer to the other by packets. A packet containing the

addresses of the sender and the receiver is first sent to the central hub, which then sends the packet to the designated computer.

ADVANTAGES

1. Adding new devices to the network is easy

2. If a computer stops working, the network is not affected.

3. If one piece of cable is damaged, only one computer is

affected.

DISADVANTAGES

1. It requires more cabling

2. If the central computer or server malfunctions, the entire network will

fail.

3. Only one computer on the network can send data at any particular time.

RING TOPOLOGY

The cable is connected to all the computers on the network. The ends of the cable are then connected together to form a loop or ring.

Data is passed from one computer to the next by means of a token (electronic signal), which is passed around the ring, giving each

computer an opportunity to send data. A computer can send data only when it is possession of the token.

ADVANTAGES

1. If a computer stops working, the other computers can

continue to communicate.

2. Communication is usually faster than with a line network.

DISADVANTAGES

1. If the main cable is damaged, the entire network goes down.

2. The entire network has to be shut down for any maintenance to be carried

out.

3. The network becomes very difficult to maintain if it gets very large.

LINE/BUS STARRING

Questions

Draw 3 LAN topologies and state what happens if one computer crashes , the server crashes or the cable is cut.

Describe a client/server relationship and state where in the school have you seen this at work?

Client / Server: is a way to setup a network in which a computer is designated as being the server and other computers are clients. The server is responsible for security and other functions like a print server, mail server or to log onto a network for username and password. Servers normally are faster and have more memory.Peer to Peer network : any computer is free to send/receive data to/from any other computer. There is no one in charge this network is like the opposite to client /server

The opposite to the client/server network is a peer to peer network : A P2P network is one in which any computer can send to any other computer , no computer is in charge.

MAN: Metropolitan Area Network covers a geographical area like a city or university campus.

Satellites relay information to each other in order to transmit data from opposite sides of the world. Line of sight is important ie nothing must be between them to interrupt the signal

WIDE AREA NETWORK (WAN)

A Wide Area Network (WAN) is a network that covers a wide geographical area. WANs use a combination of fibre-optic cables and

telephone lines, as well as satellite and microwave technology, to transmit data.

Fibre-optic cables are extremely thin cables that allow extremely fast and accurate transmission of large volumes of data.

The internet is a connection of computers worldwide.

There are 4 main types of services available on the internet Terminal Emulation Services (TES) File Access and Transfer Services Communication Services The World Wide Web.

TES- you connect to a remote host computer that allows you to feel as though you are in control eg databases, library catalogues and chat services.Telnet is software that allows for the connection to be made to the Telnet server.

File Access and Transfer Services: This service allows you to upload and download files from a remote computer using FTP(file transfer protocol) software.

The internet started out from world warII then linked universities then was expanded internationally.

To get on the internet you need a computer a communication link using a modem, an Internet Service Provider(ISP- Flow), computer software (TCP/IP service running and a Browser)

Each computer on the internet has an IP address – 32 bit number eg 196.361.204.45. But we can remember IP numbers so they developed the DNSDomain Naming System which allows humans to remember the name of a site like Google or Mathsisfun.org. Examples of top level domains are .com, .edu, .org , .gov, Page 100.

Questions

What are 4 services provided by the internet.?

UWI belongs to what top level domain?

What are 4 advantages and 4 disadvantages of the internet?

List the requirements for getting onto the internet

What is a modem and what type of modem provides the internet to your home?

What do the acronyms ISDN and ADSL stand for?

Describe the 3 links possible to the internet (i) SLIP/PPP(ii) Dedicated (iii) Remote

An email address is made up of a username and a domain name.

Mail Server is software that actually stores your mail remotely and through your mail client software you ask the server for your mail.

Questions

Describe how the following work Mailing ListNewsgroupBulletin BoardMultimedia ChatSMS

Why do you need a user name and password for email.?

What are two advantages of using email as opposed to using the phone?

Skype is form of VoIP , discuss how using Skype is VoIP and how it works.

Questions

Related Web pages written in HTML and having hyperlinks are what make up a web site. What does HTML stand for and what is a hyperlink?

What is a web server and web client?Name 3 web clients.

Special software is sent out to find new sites . What is the name of this software?

Another name for a search engine is a ____________?

Using an actual example for a URL(universal resource locator) address, identify the Protocol, Server, Path and File name eg URLhttp://www.mathsisfun.com/algebra/introduction-multiply.htmluse your own URL please.

Have you ever used advanced searching. Try it and describe how you implemented it.

Questions Four new services on the internet are Webcast, Webinar, Web2.0 and Wiki. Describe what each offers.

What are the differences between a Wiki and a web site

How should podcasting be used in schools?

List 3 types of application included in Web2.0

Give two examples of how a browser can be used forBusiness Purposes and Personal Use.

A company would have an intranet and an extranet.What is the purpose of an intranet and extranet.?

PROTOCOL

Protocols are a set of rules and procedures governing the transmission and receiving of data. Some international protocols are HTTP,

PPP, TCP/IP and FTP.

Protocols are used to ensure that transmissions are coordinated with minimal interference.

DISADVANTAGES OF NETWORKING

1. Networks are expensive to set up. In addition, configuring a network is a very complex process that may require an additional

employee.

2. Security problems. People may be able to access shared information that they are not supposed to see by hacking into

computers on the network.

MODEM (MODULATOR/DEMODULATOR)

A modem is a device that can convert digital signals into analogue and vice versa. The speed of a modem is measured in bits per

second (bps).

TERMS ASSOCIATED WITH DATA COMMUNICATION

1. UPLOAD – this is the process by which one computer, the host, sends a file to a remote computer via communication

channels.

2. DOWNLOAD – this is the process by which a computer obtains a file from a host computer via communications channels.

3. POINT-TO-POINT TRANSMISSION – this is the process by which data is sent from one location to another.

4. BROADCAST TRANSMISSION – this is the process by which data is transmitted in such a way that any person with the

correct equipment can receive it. This means that it is difficult to control who receives the data.

5. BULLETIN BOARD – this is a centralized computerized location to which remote computers can connect. Once connected,

a user can upload messages and files or download those posted by other users.