Network and Communication

A complete notes on Network and Communication for BCA, BIM and BIT students. Topics: Overview of network,LAN,WAN,MAN, Bus topology,star topology,ring topology,guided media,coaxial cable,data,communication,half duplex,full duplex, network protocols,tcp ip protocols, application, osi models

Network and Communication

Network and Communication

Overview of Network:

The communication is movement of data from one part of the system to another. The early communication is between human being they used letter and message are used as media. The transmission media of the message was horse, train, cars, and human themselves.

But nowadays network is been advance which use electronic medium to transfer the data and messages. A computer network is a group of computer systems and other computing hardware devices that are linked together through communication channels such as physical, through wires, cables, and wireless media and logical, through the transport of data across the physical media to facilitate communication and resource-sharing among a wide range of users.

One of the earliest examples of a computer network was a network of communicating computers that functioned as part of the U.S. military's Semi-Automatic Ground Environment (SAGE) radar system. In 1969, the University of California at Los Angeles, the Stanford Research Institute, the University of California at Santa Barbara and the University of Utah were connected as part of the Advanced Research Projects Agency Network (ARPANET) project. It is this network that evolved to become the internet.

Networks are used to:

  • Facilitate communication via email, video conferencing, instant messaging, etc.
  • Enable multiple users to share a single hardware device like a printer or scanner.
  • Enable file sharing across the network.
  • Allow for the sharing of software or operating programs on remote systems.
  • Make information easier to access and maintain among network users.

Types of Transmission

Transmission is the process of transferring data from one location to another which consist to mainly two types of transmission technology such as:

Analog Communication: it is a kind of communication in which information is transmitted by modulation a continuous signal, such as a sound wave, TV and Radio signal etc.

Digital Communication: In this signal are digitized, encoded and transmitted.

Data Communication and voice Communication:

Data communication refers to the exchange of data between a source and a receiver via form of transmission media such as a wire cable. Data communication is said to be local if communicating devices are in the same building or a similarly restricted geographical area.

The meanings of source and receiver are very simple. The device that transmits the data is known as source and the device that receives the transmitted data is known as receiver. Data communication aims at the transfer of data and maintenance of the data during the process but not the actual generation of the information at the source and receiver.

Datum mean the facts information statistics or the like derived by calculation or experimentation. The facts and information so gathered are processed in accordance with defined systems of procedure. Data can exist in a variety of forms such as numbers, text, bits and bytes.

Data can be analog or digital. Voice and Videos are the example of analog data which takes continuous value in some interval.

The Figure is an illustration of a simple data communication system.

Fig: Simple data communication system

A Communication system has following components:

  1. Message: It is the information or data to be communicated. It can consist of text, numbers, pictures, sound or video or any combination of these.
  2. Source: the message to be communicated is produced by the source. It can send in any form that then convert in to binary or digital bit stream.
  3. Transmitter: It generate transmittable signal for the transmission system which is analog signal.
  4. Transmission System: It is the channel or physical path through which the message is carried from sender to the receiver. The system can be wired like twisted pair wire, coaxial cable, fiber-optic cable or wireless like laser, radio waves, and microwaves.
  5. Receiver: Receiver accepts the encoded signal and produces the digital signal and send to the destination.
  6. Destination: In the final stage, destination gest the original message.

The data flow between communication devices may be simplex, half-duplex, and full-duplex.

Simplex: the communication is unidirectional, as on a one-way street. Only one of two devices on a link can transmit and other can only receive. Eg: Keyboard can only input data and traditional monitor can only display data.

Half-Duplex: In this mode each station can both transmit and receive data but not at the same time. When, one device is sending the data, other can only receive, and vice-versa. Eg: Walkie-talkie.

Full-Duplex: Both station can transmit and receive the data simultaneously. Eg: Telephone line.

Types of Computer Network:

A computer network is a group of computers linked to each other that enables the computer to communicate with another computer and share their resources, data, and applications.

A computer network can be categorized by their size. A computer network is mainly of three types:

  • LAN(Local Area Network)
  • MAN(Metropolitan Area Network)
  • WAN(Wide Area Network)

LAN (Local Area Network)

Local Area Network is a group of computers connected to each other in a small area such as building, office. LAN is used for connecting two or more personal computers through a communication medium such as twisted pair, coaxial cable, etc. It is less costly as it is built with inexpensive hardware such as hubs, network adapters, and Ethernet cables. The data is transferred at an extremely faster rate in Local Area Network. Local Area Network provides higher security.

Fig: LAN

MAN (Metropolitan Area Network)

A metropolitan area network is a network that covers a larger geographic area by interconnecting a different LAN to form a larger network. Government agencies use MAN to connect to the citizens and private industries. In MAN, various LANs are connected to each other through a telephone exchange line. It has a higher range than LAN.

Fig: MAN

WAN (Wide Area Network)

A Wide Area Network is a network that extends over a large geographical area such as states or countries. A Wide Area Network is quite bigger network than the LAN. A Wide Area Network is not limited to a single location, but it spans over a large geographical area through a telephone line, fiber optic cable or satellite links. The internet is one of the biggest WAN in the world. It is widely used in the field of Business, government, and education.

Fig: WAN

Network Topologies:

Network Topology is the representation of a network arrangement, consisting of several nodes i.e. sender and receiver nodes, and the lines connecting these nodes. Types of network topologies are describe below:

  1. Bus Topology
  2. Ring Topology
  3. Star Topology

Bus Topology

Bus topology is the kind of network topology where every node, i.e. every device on the network is connected to a solo main cable line. Data is transmitted in a single route, from one point to the other. We cannot transmit data in both ways. When this topology has precisely two endpoints, it is known as Linear Bus Topology. It is mostly used for small networks.

Fig: Bus Topology

Ring Topology

Ring Topology is a type of topology in which every computer is connected to another computer on each side, with the last computer being connected to the first, thus forming a ring shape. This topology allows for each computer to have exactly two neighboring computers.

Fig: Ring Topology

Star Topology

Star Topology is the kind of network topology in which all the nodes are connected via cables to a single node called hub, which is the central node. The hub can be active or passive in nature. Active hubs contain repeaters, while passive hubs are considered as non-intelligent nodes. Each node contains a reserved connection to the central node, which the central node acting as a repeater during data transmission.

Fig: Star Topology

Transmission Media:

Communication media refers to the means of delivering and receiving data or information. In telecommunication, these means are transmission and storage tools or channels for data storage and transmission. Communication media may be with wired or wireless. In wired signal travels along the cable from one device to another. But in wireless transmission the electromagnetic waves are transmitted without using physical wire or conductor.

Guided Media:

In guided media, transmitted data travels through cabling system that has a fixed path. For example, copper wires, fibre optic wires, etc.

The most popular guided transmission media are described below:

Twisted Pair Cable:

Copper wires are the most common wires used for transmitting signals because of good performance at low costs. They are most commonly used in telephone lines.

However, if two or more wires are lying together, they can interfere with each other’s signals. To reduce this electromagnetic interference, pair of copper wire is twisted together in helical shape like a DNA molecule. The advantage of twisting is that both wires are equally affected by external influences and unwanted signals are cancelled out.

Up to 25 twisted pairs are put together in a protective covering to form twisted pair cables that are the backbone of telephone systems and Ethernet networks.

Twisted pair is two types

Shielded Twisted Pair (STP): each pair is wrapped with an additional metal shield, then, all pairs are wrapped in a single outer plastic sheath.

Unshielded Twisted Pair (UTP): all pairs are wrapped in a single plastic cover.

Fig: UTP and STP twisted pair cable

Coaxial Cable:

Coaxial cables are copper cables with better shielding than twisted pair cables, so that, transmitted signals may travel longer distances at higher speeds. A coaxial cable consists of these layers, starting from the innermost −

  • Stiff copper wire as core
  • Insulating material surrounding the core
  • Closely woven braided mesh of conducting material surrounding the insulator
  • Protective plastic sheath encasing the wire which is outside insulation. Coaxial cables are widely used for cable TV connections and LANs.

Fig: Coaxial Cable

Optical Fiber:

Thin glass or plastic threads used to transmit data using light waves are called optical fiber. Light Emitting Diodes (LEDs) or Laser Diodes (LDs) emit light waves at the source, which is read by a detector at the other end. Optical fiber cable has a bundle of such threads or fiber bundled together in a protective covering. Each fiber is made up of these three layers, starting with the innermost layer:

  • Core made of high quality silica glass or plastic
  • Cladding made of high quality silica glass or plastic, with a lower refractive index than the core
  • Protective outer covering called buffer

Note that both core and cladding are made of similar material. However, as refractive index of the cladding is lower, any stray light wave trying to escape the core is reflected back due to total internal reflection.

Unguided Media:

In unguided media, transmitted data travels through free space in form of electromagnetic signal. For example, radio waves, lasers, etc.

Following are the example of unguided media.

Microwave System:

Microwave transmission is the line of sight transmission. The transmit station must be in visible contact with the receiver station. This sets a limit on the distance between stations depending on the local geography. Typically, the line of sight due to earth’s curvature is only 50 km to the horizon. So, the repeater station should be placed on this distance. It is relatively inexpensive, putting up two tower and antennas for each is cheaper then 50 km ling fiber cable.

Example of microwave system is mobile phone network, television distribution etc.

Fig: Microwave system

Here in this figure we can see, Station A sends the voice data to the Repeater site 1 with 1.2 GHz frequency. Then Repeater Site 1 sends data to another tower with 10 GHz frequency which forwards that data to Repeater Site 2. And finally Repeater Site 2 sends that data to the Station C with 1.2 GHz frequency.

Communication Satellites:

It is also a kind of line of sight transmission. Satellite stations are set in geo-stationary orbits directly cover the equator, which rotates in synchronization to earth and hence look stationary from any point on the earth. Those geo-stationary orbits are placed 36,000 km above the earth’s surface. The communication is carried through uplink and downlink. The uplink transmits the data to the satellite and downlink received the data from satellite. The area shadowed by the satellite in which the information or data can be transmitted and received is called footprint.

Communications satellites are commonly used for mobile phone signals, weather tracking, or broadcasting television programs.

Fig: Communication Satellite System

Here in the figure we can see that, Transmitting dish antenna in the transmitting earth station sends the data to satellite using uplink frequency. When satellite received the data then it send those data to receiving dish antenna in the receiving earth station using downlink frequency.


An infrared transmission is a wireless technology used for communication over short range. The frequency of the infrared is in the range from 300 GHz to 400 THz. It is used for short-range communication such as data transfer between two cell phones, TV remote operation, data transfer between a computer and cell phone resides in the same closed area.

Network Protocol:

Network protocols are formal standards and policies comprised of rules, procedures and formats that define communication between two or more devices over a network. Network protocols govern the end-to-end processes of timely, secure and managed data or network communication. There several types of network protocols such as TCP/IP, UDP, IP, FTP etc.


TCP/IP stands for Transmission Control Protocol/Internet Protocol. TCP/IP is a set of layered protocols used for communication over the Internet. The communication model of this suite is client-server model. A computer that sends a request is the client and a computer to which the request is sent is the server. It is the connection-oriented protocol which means sender and receiver should establish the connection before communicate and it will be terminate after finishing the communication.

  • TCP/IP enables two hosts to establish a connection and exchange stream of data. Stream is simply the sequence of data bytes. It guarantees the delivery of the data and also guarantees the packet of data will be delivered on the same order as they are sent.
  • TCP is a connection-oriented protocol that is responsible for reliable communication.

Unlike the OSI model which has seven layers architecture, TCP/IP reference model has four layers architecture. Following architecture illustrates TCP/IP reference model.

  1. Application Layer

This layer provides applications the ability to access the services of the other layers and defines the protocols that applications use to exchange data. This layer adds its own header and sends down to the Transport layer.

Some of the popular protocols of this layer are: HTTP, FTP, SMTP, Telnet etc.

  1. Transport Layer

It is mainly responsible for providing the application layer with session and datagram communication services. It accepts data from application layer splits it up into smaller units and pass these to the network layer. This layer adds its own headers and sends down to the Internet layer.

It is the responsibility of this layer to ensure that all the split pieces arrive correctly at the other end. It is concerned with end-to-end transportation of data and setups up a logical connection between the hosts.

There are two protocols available in this layer: TCP and UDP.

  1. Internet Layer

The segments sent by the above layers are received here. Now, we need to send this segment of data to a destination host which could be anywhere (in the same network or may be external network). This layer ensures that the segment is moved

across the networks to the destination network. It provides logical addressing, path determination for the segments to be sent and forwarding.

This layer also adds its own headers and converts and sends the received segments in form of packets.

Some of the popular protocols of this layer are: Internet Protocol (IP), ICMP, etc.

  1. Network Access Layer (Data Link + Physical Layer)

This layer defines the protocols and hardware required to connect a host to a physical network and to deliver data across it. For delivery within a given physical network, packets are sent from the above layer to this layer.

The destination can be another host in the network, itself, or a router for further forwarding. So the Internet layer has a view of the entire Internetwork whereas the Network Access layer is limited to the physical layer boundary that is often defined by a layer 3 device such as a router.

The protocols in this layer depend upon which physical network is being used. When the physical network is LAN, Ethernet (802.3) and its many variants are used while if the physical network is a WAN, protocols such as Point to Point Protocol (PPP) and Frame relay are common.