Introduction to Networking and Data Communication
Networking and Data Communication Terminologies

By the end of the lesson you should be able to:

  • Define networking terminologies

Computer Network: Refers to two or more computers connected together using data transmission media for the purpose of sharing information and network resources

Data Communication: The process of transmitting data signals through networking media from one place to another


By Khairil Yusof from Malaysia - RJ45 Ethernet Cable, CC BY 2.0,

Data Communication

By the end of the lesson you should be able to:

  • Define data communication terminologies

Data Communication Terminologies

Data signal - This refers to voltage level that flow in a circuit denoting a given information.

Analog Signal - Refers to electrical signal that varies continuosly in a circuit

Digital Signal -refers to a sequence of discrete pulses of 1's and 0's. Here the voltage above a certain level is considered 1 and voltage below the same level is considered 0

Serial Data Transmission - Data is transmitted over a single communication path. Bits are  tranferred down the line one at a time.

Parallel Data Transmission - Data is transffered using several transmission paths.

Signal Modulation and demodulation - Modulation refers to conversion of digital signals to analog signals at the transmission end while demodulation refers to conversion of analog data back to digital at the receiving end. The device that performs demodulation and modulation is known as Modem

Multiplexing - refers to the process of transmitting difference data signals on the same communication medium.

Demultiplexing - refers to the process of separating the multiplexed signal at the receiving end

Bandwidth - Refer to the amount of data that can be transferred by a transmission medium per second.

Baseband signal - digital signal generated and applied to transmission medium without modulation.

Broadband transmission- this where an analog signal is sent over a transmission medium using a particular frequency

Attenuation - this refers to loss of strength of data signals during transmission through a data transmissin medium

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Modes of Data Communication

By the end of the lesson you should be able to:

  • State and define the three modes of data Communication

Simplex Mode: it is used when data is transmitted in one direction only. For example, in radio broadcasting, the listener cannot communicate back through the radio receiver.

Half Duplex: Used when two interconnected devices wish to exchange data alternately, that is, the two devices switch between send and receive modes after each transmission. An example is a radio call

Full Duplex/Duplex transmission: Here data is exchanged between the devices in both directions simultaneously.An example in communication through cell phone

By Harke - Own work, Public Domain, NIC

Types of Computer Networks

By the end of the lesson you should be able to:

  • Identify and describe types of computer networks

Computer networks are classified into

  • Local Area Networks(LANS)
  • Metropolitan Area Networks(MAN)
  • Wide Area Networks(WAN)

Local Area Network

This a network formed when computers are connected together in a small geographical area of upto 3km radius, for example on the same floor, building or block of buildings

Characteristics of LANs are:

  • Occupy only small physical location
  • They are either peer-to-peer or client/server networks
  • Have high-speed data transfer rates
  • All data is part of local network

Metropolitan Area Network

A MAN  covers a medium sized geographical area, such a town. MAN connects several LANs together using high-speed telephone lines, such as leased lines or wireless communication

Wide Area Network

WAN  cover unlimited geographical areas across the country and entire world .

Purpose and Limitations of Networking

By the end of the lesson you should be able to:

  • explain the purpose of a computer network
  • explain the limitations of computer network

Purpose of Networking

  • Computer networks enable the sharing of centrally located data
  • Enables sharing of  hardware
  • enable sharing of software
  • enables Central control of data, hardware, and software.
  • increases efficiency due to the high speed of  information communication

Limitations of Networking

  • slow response time
  • access limitations for shared resources
  • risk of tampering by hackers

Public Domain,Cable Modem LInk

Data Communication Media Lesson I

By the end of this lesson you should be able to:

  • To define data communication media
  • Describe different types of bounded communication media

Data communication media refers to the pathway through which data signals are transferred from on place to another. Data Communication media are classified as:

  • Bounded communication media(use of cables/wired)
  • Unbounded communication media(wireless )

Bounded Communication Media

In this type, data signals are relayed through cables. These media are again divided into :

  • Two open cables
  • Twisted pair cables
  • Coaxial Cables
  • Fibre optic Cables

Two wire open line cables

These are made up of two parallel copper wires separated by a plastic insulator. They are used to transmit voice signals over telecommunication networks. This type of bounded media suffer from EMI as the lines are parallel to each other.

Twisted Pair Cables

These are copper wires wound on each other. The winding/twisting reduces electromagnetic interference and crosstalk. They are divided into:

  • Unshielded twisted pair (UTP)
  • Shielded Twisted Pair (STP)


Unshielded Twisted Pair (UTP)

They are not shielded using braids of copper wire or aluminium foil. They suffer from electromagnetic interference. These interferences may come from lightning sparks, radio signals etc.

Advantages of TP cables

  • It is cheap due mass production of for telephone use
  • Installation of equipment is cheap and readily available
  • It is easier to set up network  omedia because connection is readily available

Disadvantages of TP cables

  • it suffers from loss of strength of data signals
  • It is prone to electromagnetic interference and eavesdropping
  • It has low transmission rates as compared to other cables

Shielded Twisted Pair (STP)

Here, shielding  is done by use braided copper wires and aluminium foil to prevent electromagnetic interference

By Hurzelchen, CC BY-SA 3.0,

Twisted pair Cable

Data Communication Medial Lesson II

By the end of the lesson you should be abe to:

  • Describe fibre optics
  • Explain how fibre optic transmit data
  • state various types of fibre op[tic

Fibre Optic Cables

Transmit data signal by use of light. The electrical signal is converted by Light Emitting Diodes(LED) to light signal. The light signals then travel through the core of the optic fibre by a series of total internal reflection. The light used is an infrared laser. There is usually less interference for data signal transmitted this way so fibre optics have high bandwidth compared to twisted pair and coaxial cables

Parts of fiber optic cables:

  • core- central hollow part. Transmits light signals
  • cladding - has light-bending characteristics
  • coating/buffer - strengthens the cable
  • strengthening fibres -
  • cable jacket- the outer covering

Types of optic fibre optic cables

  • single-mode - transmits a signal by using a single ray of light
  • multimode- transmits  signals by using several rays of different angles of incidence


Network Topologies

By the end of the lesson you should be able to:

  1. Describe bus, ring, and star topologies
  2. state the advantages and disadvantages of each topology

Topology - refers to how the nodes of a network are connected.

Types of Topology

  • star topology
  • ring topology
  • bus topology

Star Topology

This is where all cables for each computer is being connected directly to the server via a hub or a switch. This implies that for hosts to communicate they have to do so through the server


  • each computer has a direct line to the server hence communication is very fast
  • when there is a fault on the wire linking the host and the server, there is no interference with the rest of the network i.e it is reliable.
  • a node can be added or removed without interfering with the entire network i.e it scalable
  • network management can be done centrally


  • failure of the central switch node may bring down the entire network
  • more cabling is required hence expensive

Bus Topology

This is where is a single central trunk/cable/backbone/bus on which all the workstations are connected. Usually, the trunk/bus/backbone has a terminator on both ends to prevent signal loss.


  • new computers can be added without disrupting other computers
  • installing a bus topology network is easy
  • it is less costly


  • any fault/breakage along the backbone brings down the whole network
  • determining the point of failure is very difficult
  • since there is a high rate of collision during data transmission, very few computers can be connected to the network at a time
  • every workstation can see all the data on the network

Ring Topology

it is where the workstations are set out in a ring using a cable. A token is usually passed along the ring from node to node and if the token is meant for a given node then it releases the information to the network


  • uses a shorter cable hence economical
  • it easy to install
  • it provides high speed unidirectional communication


  • if any computer breaks down, communication is hampered in the ring

Network Topologies Link


Network Software

By the end of this lesson, you should be able to:

  • state the network application software
  • state and explain the seven layers of OSI model

Network software


  • network protocols and Network Operating System

Network Operating Systems

Most servers run on Network Operating System. This OS is used to control and serve client computers

Functions of Network Operating Systems

  • securing all network resources
  • sharing network resources

Examples of Network Operating System

  • Novell Netware
  • Windows NT/2000/2003
  • various versions of Unix
  • Linux

Network Protocols

A protocol is a set of rules used that guide communication of networked devices

Due to the fact that computers and various devices on a network may be running on the different operating systems, the ISO came up OSI (Open Systems Interconnection ) model to enable such devices to interoperate.

The OSI model has 7 main layers:

  • Application layer
  • Presentation layer
  • Session layer
  • Transport layer
  • Network layer
  • Datalink layer
  • Physical layer

NB: Each of the above layers uses a package of protocols:

Application Layer

This layer uses protocols such as HTTP, SMTP, FTP, Telnet, etc. It provides services for network applications. This is the layer at which network applications operate e.g  internet browsers, email apps,

HTTP/S - used for web surfing through browsers

SMTP - used for email through email apps

FTP - File transfer

Presentation Layer

This layer receives data from the application layer. It converts this data to machine-readable form. So, this layer does more of data translation. It also compresses the translated data so as to be transmitted faster. This layer encrypts data before transmission. Secure Socket  Layer (SSL) Protocol is for encryption and decryption.

Session Layer

This layer helps in:

  • session management
  • authentication
  • Authorization

This layer uses APIs to help it perform the above functions. NETBIOS is an example of API(Application Programming Interface)

Note: The web browsers perform all functions of the application, presentation, and session layer

Transport Layer

Controls the reliability of communication through:

  • segmentation: data received from the session layer is divided into smaller data units each containing a destination's sequence number and port number. The port number helps to direct each of the segment to the correct application while the sequence number helps to reassemble the segments to form the correct message
  • error control: if some data do not arrive at the destination transport layer uses an automatic repeat request scheme to retransmit the data
  • flow control: controls the amount of data transmitted from the server to the DTE depending  on the DTE's processing power

Protocols at this layer include: TCP and UDP

UDP(User Datagram Protocol)  is faster than TCP

TCP - Deals with a connection-oriented transmission

  • lost data can be retransmitted.

UDP - Deals with a connectionless transmission

  • lost data not retransmitted.

Network Layer

  • Receives data segments from Transport Layer
  • Transmit data segments in form of a packet from one computer in a given network to another computer in a different network
  • This is the layer where routers fall
  • This layer assigns the senders IP and receiver IP to the data segments to form data packets

Functions of the network layer:

  • Routing - the process of moving data packets from source to destination
  • Logical addressing: IPv4 and IPv6
  • path determination: network layer uses Open Shortest path First(OSPF), Border Gateway Protocol(BGP), and Intermediate System to Intermediate System(IS-IS) to determine the shortest optimal path

Data Link Layer

  • receives packets from the network layer
  •   physical addressing is done at the data link layer where MAC addresses of the sender and receiver computers are assigned to data packets to form a frame.
  • the data link layer is embedded in a computer's NIC as a software
  • involved in the transmission of data through local media


  • Accesses the media by use of framing
  • Controls how data is placed and received from media

Physical layer

  • Converts bits to signals and vice versa

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