Introduction to the Computer Network

Data Communication

Exchange Data from source to destination via  transmission media is called data communication.

Eg:

• Newspaper
• Radio
• Telephone
• Internet

Data communication modes

• Simplex mode
  One-way communication is only possible. The sender can only send the data, and the receiver can only receive the data.
  Eg:
  TV telecasting, Radio broadcasting
  

• Half  Duplex mode
  Two-way communications is possible but not simultaneously. The sender and receiver can both send and receive the information, but only one is allowed to send at any given time.
  Eg:
  walkie-talkies

• Full Duplex mode
  Two-way communications is possible simultaneously. The sender and receiver can both transmit and receive at the same time.
  Eg:
  PSTN (land phone), Mobile phone, Internet
  PSTN-Public Switched Telephone Network
  

Basic Requirements for data Communication

Message
Data to be communicated.(text, numbers, pictures, sound or video or any combination of these)

At least two parties
(Sender, Receiver)

Medium
It is the channel or physical path through which the message is carried

Communication Rules (Protocol)
It is a set of rules that govern the communication between the devices. Both sender and receiver follow same protocols to communicate with each other.

Fundamental characteristics of data communications

Delivery
The data must be deliver in correct order to correct destination.

Accuracy
Deliver accurately

Timeliness
Deliver data on time

Networks

Road Network
Telephone Network
Computer Network

Computer Network

Computer Network, two or more computers that are connected with one another in order to share resources such as files, database, software, hardware etc.

Advantages of computer network

• Sharing of data/information.
• Sharing of database/file.
• Sharing of hardware.
• Easy to communicate.

Disadvantage of computer network

• Possible threat of virus.
• Possible threat of unauthorized data access such as hacking.

Types/Examples of computer networks

• PAN-Personal Area Network
  PAN is a computer network used for communication among computerized devices, including cell phone and personal digital assistants.

• LAN-Local Area Network
  LAN is a computer network that inter connects computers in a limited area such as a home, school, computer laboratory, campus or office building.

• MAN-Metropolitan Area Network
  MAN is large computer network that spans a metropolitan area, its geographic scope falls between WAN and LAN.
  Eg:
  Network of a company which spread over several cities of a country. (Bank network)

• WAN-Wide Area Network
  WAN is a telecommunication network that covers a broad area. Its spans over a country or between country. It is a network of networks. The largest wide area network is Internet. The internet provides many facilities such as e-mails, WEB, Social medias, Online-Shopping, Ecommerce etc.
  Eg: Internet, Bank networks

Data Communication Media

• Wired media / cable/ bounded media/guided media.
  Examples:
  Twisted pair cable
  Consist of pairs of copper wires twisted together and then contained in an outer casing.
  
  Co-axial cable
  Consist of copper wire with an insulation shield from another conductor and finally another insulator around the whole thing. Due to the natural resistance to the conductor, The distances possible are limited.
  
  Fiber-Optic cable
  Consist of a large number of very fine glass strands down which pulses of light can be sent. The means of communication is light rather than electrical signal therefore message interference free and it is not easy to hack by outsiders.

• Wireless media/radiated media/unbounded media/unguided
  Examples:
  Infrared (IR)
  Uses pulses of infra-red light to send coded signal. eg: remote controls and TV
  
  Microwave
  Highly directional and is used to transmit large quantities of data between fixed positions.
  
  Bluetooth
  Wireless connections over a very short distance and slow connection. It is used to connect peripheral devices such as phone to phone / Phone to computer
  
  Wi-fi
  Wireless connection using radio waves. The possible ranges are dependent on the environment factors. It can cover a geographical area such as a school or home.
  

Types of Network Topology

Layout of the network. The way the different nodes are connected to each others.

• Bus
  Servers and Workstations are connected to the central communication channel. Each node is directly connected to the channel.
  Advantages
  Construct a network easy
  Easy to connect a node to the network
  One computer failure won't affect other computers in the network
  
  Disadvantages
  High Traffic (Because all the computers are connected to the central channel)
  Central Channel broken then no more network.

• Ring
  Each and every computers in the network is directly connected with 2 other computers. (Connected as a ring)
  Disadvantages
  One computer is affected, Network is broken
  Difficult to connect new computer to the network
  

• Star
  Computers are connected in the network like a star. Each stations are connected directly to the Hub/Switch.
  Advantages
  Easy to connect a new computer to the network
  If one computer is broken, Other computers in the network won't be affected.
  
  Disadvantages
  If the switch/Hub is broken then all the computers in the network will be affected.(no more network)

• Mesh
  Each and every computers are directly connected to all other computers/workstations in the network.
  Advantages
  if one computer in the network broken, it won't affect other computers in the network.
  
  Disadvantages
  It is a complex network topology
  Construct this type of network is difficult and expensive.