NETWORKING AND DATA COMMUNICATION

Definition of terms used in Networking

Network

A Network can be defined as a collection of independent entities that are arranged in such a manner as to exchange data, information or resources.

Examples of networks:

  • Road network: – this is the interconnection of roads in a country, continent or throughout the world. Road networks facilitate the transfer of goods & services from one area to another.
  • Telephone network (voice networks): – it includes the many lines that criss-cross a country, and enables people to communicate.
  • Railway network.
  • Nervous system.

Computer Network

A computer network can be defined as a collection 2 or more computers connected together using transmission media (e.g., telephone cables, or Satellites) for the purpose of communication and sharing of resources.

Usually there can be from 2 to hundreds or even thousands of computers on the network.  Apart from computers, other devices such as Printers, plotters, fax machines, modems, etc can also be connected to the network.

The term Transmission media refers to any physical or non-physical link between 2 or more computers, and in which a signal can be made to flow from source to destination.

Network Server.

Computer networks usually have one computer reserved as the “Mother” of all the other computers on the network.

A Server is a powerful computer that provides services (shared resources) to the other computers on the network.  It enables information, resources & network devices to be shared by users on a computer network.

Network servers;

  • Have a higher hard disk & main memory (RAM) capacity than the other computers on the network.
  • Store & run a special program called the server software (network operating system), which controls computers on the network.

Clients (workstations)

Clients (also referred to as Workstations) are Personal Computers (PCs) attached to the network, on which the network users do their work.  They are used by network users to send their requests to the server.

Clients;

  • Are usually less powerful than the server, and use the resources provided by the Server.
  • Have their own operating systems and files.

The PCs can be IBM or compatible running MS-DOS, OS/2, Windows, etc.

The figure below shows a server on a network.

DATA COMMUNICATION

Data communication refers to the process of transmitting data signal from one place to another through a communication media.

The basic components of a data transmission system are:

  • A central computer.
  • Terminal devices.
  • Telecommunications link between the central computer & the terminal devices.

Terms used in data communication

Data signal:

A data signal is a voltage level in the circuit which represents the flow of data.

In data communication, there are 2 types of data signals; Digital and Analog.

Analog data is made up of continuous waveform, while digital data is made up of a non-continuous discrete waveform.

Analog data

Time

Velocity

 

Signal modulation and demodulation:

This is the process of converting data signals to a form that can be transmitted over a transmission medium.

E.g., a modem converts a digital signal to an analog signal, which can be transmitted over analog telephone lines.  This process is called modulation.  A modem at the receiving end converts the analog signal into a digital signal, a process known as demodulation.

 

Multiplexing and Demultiplexing:

Multiplexing is the process of sending multiple data signals over the same medium, e.g., a wire conductor can be made to carry several data signals either simultaneously or at different times.

Demultiplexing is the process of separating the multiplexed signals at the receiving end.

Illustration:

Town A has 10 computers which want to communicate with 10 other computers in town B.  In a normal case, it will need a direct cable linking each of the computers in town A to its partner in town B.  However, if multiplexing is used, the computers can be made to share a single cable laid between the two towns, hence, saving cost.

 

The different data signals have different frequencies on the cable; hence, they do not interfere with one another

Frequency (f):

Frequency of a wave is the number of cycles made by the wave in 1 second.  Frequency is measured in units called Hertz (Hz); where 1 Hz is equivalent to 1 cycle/second.

Baud:

This is the unit to measure the speed of transmission.  Generally, 1BAUD is 1bit/second.

Baud rate:

This is the rate at which data is transferred or transmitted.  It is measured in Bits per second (bps).

Band:

The rate of change of a signal on a transmission line.

Bandwidth:

A Bandwidth is the maximum amount of data that a transmission medium can carry at any one time.  E.g., a certain cable may have a bandwidth of 100 Mbps (Mega bits per second).

Guardband:

This is the range of frequency that is used to separate two channels.

Baseband signal:

This is a digital signal that is generated and applied to the transmission medium directly without modulation.

Note.  A baseband signal utilizes the full capacity of the transmission medium; hence, at any one time, only one signal can be sent.  However, multiple signals can be sent at different times, if they are multiplexed.

Broadband transmission:

This is where an analog signal is sent over the transmission medium using a particular frequency.  This means that, several data signals can be sent at the same time through the same medium, but at different frequencies so as to prevent them from overlapping.

Attenuation:

Attenuation is the decrease in magnitude and energy of a signal as it progressively moves along a transmission medium.

If the signal is not boosted, it will totally be lost along the way, and may never reach the destination.

Attenuation (or signal loss) is usually corrected by placing signal amplifiers (also called repeater stations) along the medium at appropriate distances in order to receive the weak signal, clean it, amplify it, then re transmit it.

Modes of data communication

There are 3 modes of data communication:

  • Half duplex.
  • Full duplex.

Simplex transmission:

This is where communication is only in one direction (as in radio or television broadcast).  The listener or viewer cannot communicate back through the radio or television receiver back to the broadcaster.

Half duplex transmission:

This refers to communication in both directions, but one direction at a time.

A sender must first send the data before the recipient can reply, e.g., if two police officers are communicating using a ‘walkie talkie’ radio, one has to say “over” to mark the end of every statement in order for the other to respond.

Full duplex transmission:

This is where communication occurs in both directions simultaneously (as in computers that are sending & receiving data on a network).

Factors to consider when selecting a data transmission system

  1. Cost of each type of data transmission method.
  2. Distance between the computer & the terminal.
  3. Whether data should be transmitted direct to the computer online.
  4. Type of data transmission system to be used, i.e., whether the data transmission will be 1-way or 2-way.
  5. Volume of data to be processed; and whether it is batched at particular times, or whether it is collected individually and required to be processed immediately.
  6. Speed of transmission required.

In many cases, it is acceptable to use the ordinary Postal service, Kenyan rail, or a private Courier service.

  1. Accuracy and reliability required.

PURPOSE OF NETWORKING

Some of the reasons for setting up computer networks include

  • Resource sharing

A Network resource refers to any component that can be attached to the network for access by users.

Some of the shared resources include:

  • Application programs. vii).      Network Printers
  • Data and information. viii).    Fax machines
  • ix).       Modems
  • x).        Storage devices (optical drives).
  • xi).       Communication ports.
  • Computer processing power. xii).      Disk space

Users whose computers are connected to a network can, for example, share their files, exchange mails, send faxes, schedule meetings, and print documents from any point on the network.  This centralized access to data & information leads to less waste of time, and hence greater productivity.

  • Remote communications

Remote communication refers to the transmission of data signals between two communication devices located at different geographical locations.

E.g., using remote communication, one can work from home just as if he/she is in the office.

It is mainly through remote communications that people can be able to share ideas, and pass messages over the Internet.

A computer that tries to access resources from another computer on the network is called a remote client, while the computer being accessed is called a remote host.

Remote communication has been made possible by use of wireless transmission media such as radio waves, microwave, and satellite.

  • Distributed processing facilities

Distributed processing refers to the act of running the same programs or databases on different computers, which are on the same network but placed in separate locations.

Each computer has its own local peripherals, e.g., disks, printers, terminals, etc.

For example;

In a large organization, each branch office has its own server that stores data, information, and other resources required for their daily operations.

This implies that, files reside on the user’s computer rather than on a central computer, and are only transmitted periodically to update the central computer.

Advantages of distributed processing.

  1. Failure of the central computer does not affect the operations of the other terminals.
  2. Processing load is shared equally; hence, no time wastage.
  3. There is faster access of data as each machine can process & store its data.
  4. It doesn’t need powerful and expensive servers for data storage.
  5. It can accommodate users with variety of needs.

Disadvantages of distributed processing.

  1. It is more susceptible to virus, as any user could introduce an infected file and spread it throughout the network.
  2. Developing an effective back up plan is more difficult when users store data in their individual systems.
  3. File management (organization) is difficult as the files are stored in different locations.