What is Computer Network? Need, Advantages, Disadvantages, Characteristics, Model

What is Computer Network?

Networking, or computer network, can be defined as “A computer network is a group of computer systems and other computing hardware devices that are linked together through communication channels to facilitate communication and resource-sharing among a wide range of users. Networks are commonly categorized based on their characteristics.”

In simple terms, a computer network, also called a network, is described as two or more computers that are connected to one another for the purpose of communicating data electronically. In other words, a computer network is an interconnection of computers and computing equipment using either wires or radio waves over small or large geographical areas. A wireless network makes use of radio waves.

Simplest network of interconnected two systems is depicted in Figure.

Need for Networking

As discussed earlier, networking can also be described as a set of two or more computers that are connected together in order to share hardware resources (such as printers and CDs), and software resources (exchange data and files), or allow electronic communications. In a network, the computers may be linked with each other through cables, telephone lines, radio waves, satellites, or infrared light beams.

Figure shows the sharing of printers by three systems in a network.

In organizations, before forming a network of computers, the computer systems might have been working in isolation. These isolated systems are unable to share any hardware or software resources with the other systems. In this scenario, it becomes difficult for the company management to correlate data present on these isolated systems.

To extract and correlate information about the company as a whole, the management decides to create a network of these isolated computers. Thus, the core issue in forming a network of computers is to share the resources of an organization as a whole, be it hardware or software resources.

An organization may feel the need to have networking due to the following reasons:

Resource Sharing

The main objective here is to make all the hardware equipment, like printers, and all the information, especially data and program available to everyone who is on the network irrespective of the physical location of resources and user.

High Reliability

Copies of the data file can be kept at multiple locations in a network. Thus, if there is a hardware failure at any end of the network, other copies of the data file can be obtained from any of these locations. This ensures that the data is not lost due to hardware failure. The factor of reliability in networks is of utmost importance in many areas like banking, military, and air traffic control.


Computer systems which are part of the network are low in price and high in performance. Thus in a network, data is kept in a centralized mainframe system and the rest of the systems are personal computers which are cost-effective. This model of the network is also called client-server mode, where the mainframe system is the server and the rest are clients.


A network should be scalable i.e., it can be expanded just by adding one more system to the centralized mainframe system without adversely affecting the performance of the entire network. Rather the network can be enhanced by adding new clients.

Powerful Communication Medium

A computer network proves to be a powerful communication medium for employees who are situated at physically far distances. They can share emails and data. If one of them makes any changes in a document another can see it immediately. This quick sharing of important information over long distances also improves the performance of the organization as a whole.

Now, let us consider some of the real-life applications of computer networks:

  • Banking transactions like fund transfers, FD, RD, etc.
  • Taking out cash from an Automated Teller Machine(ATM).
  • E-mails i.e., sending and receiving mails electronically
  • Online ticket reservation for airlines, rail, and hotels.
  • Data sharing with ease in offices.

We have seen some real-life scenarios where computer networks increase the efficiency of an organization. However, computer networks have a flip side too. Let us discuss a few advantages and disadvantages of networking in the following section.

Advantages and Disadvantages of Networking

As we have seen in previous sections, computer network brings an added advantage to an organization. Some of the advantages of computer networks are as follows:

  • Information storing and sharing: Information can be easily created and managed using computers. A computer network provides a place to store information as well as the essential mechanisms and infrastructure to share that information with other users using the network.

  • Sharing of files: On a computer network, files can be stored on a central computer (also called a file server). This enables the data to be shared throughout an organization.

    Backup of files can be easily maintained when files are saved on a central file server rather than when they are scattered across separate independent computers.

  • Resource Management: For a network, software licenses are cheaper than buying licenses for several standalone computers. Network versions of the software are known to have a speedy installation on client computers than on the file server.

    Hardware devices such as expensive laser printers or scanners can easily be shared over the network. This sharing of expensive devices proves economical for the network.

  • Services: An organization, if in the public domain, can provide online services to its customers using the network.

    For instance, banks provide various facilities like applying online for a loan, online fund transfer from one account to another other, etc. A university can register students and offer various courses online.

  • Instant Messaging: Network users can communicate instantly by email and instant messenger.

  • Security: In computer networks, security is established through a centralized server by providing login credentials to authenticated users only.

    The credentials like user id and password ensure that only the authenticated users have access to the network and can access certain files, applications, and sensitive information. Establishing network security also ensures that one user cannot see other users’ files unlike on stand-alone machines.

Although whatever we have seen so far indicates computer networks enhance the overall performance of an organization, this network has some disadvantages as well.

Some of the disadvantages of Networking are as follows:

  • Expensive Installation: Network cabling, network cards, routers, bridges, firewalls, wireless access points, file server and software required for establishing a computer network can be costly.

    Thus, establishing large networks carries hefty price tags. Software installation for a large network also requires the services of technicians on a regular basis.

  • Regular Maintenance: Regular maintenance of a network is time-consuming and complicated and requires expertise and training. Thus, a full-time administrative manager needs to be employed for a large network.

  • Server Failure: Failure or breakdown of a network server brings down the entire network with it. Thus, good network design practice says that critical network services (provided by servers) should be in duplicate on the network.

    This ensures that there is no network failure in case of a server breakdown. However, it increases the overhead of maintaining a duplicate server.

  • Hardware Failure: Establishing a network entails lots of hardware in terms of cables and other devices. A broken cable or a breakdown of any device in the network can bring the entire network to a halt.

  • Security and Compliance: Network security is expensive but also very important. A network needs to be secured against computer viruses that can spread to other computers throughout the network.

    Another threat to computer networks is of hacking, particularly in larger networks. Security procedures, like firewalls, are needed to prevent such abuse.

Characteristics of Networks

Different networks are characterized by their cost, performance, and structure. We can compare the characteristics of different networking options to evaluate the networks at different levels. Following are some of the characteristics of a network:


Availability is the measure of the probability that the network will be available when required. It can be calculated as follows:


A network required to be available for 30 minutes was only available for 25 minutes. The availability of such a network can be calculated as follows:


Cost is the total expenditure incurred for setting up of a network and maintaining it on a regular basis.


Scalability is the measure of how best a network accommodates an increase in the number of users and increases in data transmission in an existing structure. A scalable network is designed in such a way that allows easy future expansions to avoid adverse effects on its existing performance.

If it is not so then high expenses will have to be incurred to transform an old network into a new one that can accommodate more users or transmits more data.


Security is a major concern in networks. For a network, it defines the level of protection of a network from misuse, intrusion, etc. Maintaining security is of utmost concern for a network to keep things in order and to avoid unwanted attacks otherwise insecure networks might cost a lot in the long run.


Reliability is the characteristic of a network that shows the level to which a network can be depended upon. This characteristic is weighed against the dependability of the network components like switches, routers, hubs etc. that are used in a network. If any of these fail then the entire network might just shut down.


Topology can be of two types i.e. physical topology and logical topology. Physical topology deals with the arrangement of physical components in a network whereas logical topology deals with the path that data signals take through the physical topology.

Network Models

While dealing with networking, the terms “network model” and “network layer” are commonplace. The network model is defined as a set of network layers and how they interact with each other and with the layers present in another network.

The two network models are:

The TCP/IP Model

The TCP/IP model is also called the Department of Defense DoD model because it was designed for the Department of Defense in the United States. TCP/IP model is a collection of communications protocols and is used for the Internet. Commonly it is referred to as TCP/IP. TCP/IP provides end-to-end connectivity between the source and destination network.

It specifies how data should be formatted, addressed, transmitted, routed, and received at the destination. The TCP/IP model has been organized into four layers which are used to sort all related protocols according to the scope of networking involved. There is an organization called the Internet Engineering Task Force (IETF) which is responsible for maintaining the TCP/IP model and related protocols.

The layers of the TCP/IP model from the lowest layer to highest layer are:

  • The Link Layer: This layer contains communication technologies for a single network segment.

  • The Internet Layer: This layer connects hosts across independent networks, thus establishing internetworking.

  • The Transport Layer: This layer handles host-to-host communication.

  • The Application Layer: This layer provides process-to-process application data exchange.

OSI Network Model

The International Standards Organisation (ISO) has defined a standard called the Open Systems Interconnection (OSI) reference model. OSI is a seven-layered architecture. The Open Systems Interconnection model (OSI) is a conceptual model that characterizes and standardizes the internal functions of a communication system by partitioning it into seven logical/ abstraction layers.

Every layer serves the layer above it and is served by the layer below it. For example, a layer that provides error-free communications across a network provides the path needed for applications above it, while it calls the next lower layer to send and receive packets that make up the contents of that path. Two instances at one layer are connected by a horizontal connection on that layer.

The seven layers of OSI model are:

  • Application Layer: It is used in applications that are written specially to run on the network. This layer allows access to network services that support applications.

  • Presentation Layer: This layer translates from application format to network format and vice-versa to enable easy transmission of data across networks.

  • Session Layer: This layer is responsible for establishing, maintaining, and ending sessions across the network.

  • Transport Layer: This layer divides streams of data into chunks or packets that can be transported across the network. It also reassembles the message from packets at the other end.

  • Network Layer: This layer translates logical network addresses and names to their physical address. It breaks the data into a smaller unit and assembles data at the other end.

  • Data Link Layer: Takes a string of bits and delivers it across a link.

  • Physical Layer: This layer defines the physical means of moving data over network devices.

Applying Communication Networks

Communication networks have been widely used in business organizations. These are used for communication within as well as outside the organization. Earlier, organizations maintained separate networks for voice, data, and video communication whereas now, there are multi-service networks available.

Multi-service networks are capable of communicating all these media together through a single network infrastructure.

These networks help in reducing the cost involved in networking and support with services and solutions as well, such as video collaboration, voice data call centers, distance learning or unified messages to combine voice mail, e-mail, and faxes. These applications need network support to be executed in an organization.

Now, let us study communication networks in a business application in the following section.


In the Intranet, multiple PCs are networked to be connected to each other. Computers in the intranet are not accessible to the world outside of the intranet. Usually, every organization has its own Intranet network and members/employees of that company can access the computers in their intranet.

Each computer in Intranet is also identified by an IP address, which is unique among the computers in that Intranet.


Extranet is a computer network that is used outside the intranet. An extranet is a computer network that gives controlled access from the outside, for specific business or educational purposes.

In an organization, an extranet can be defined as an extension of an organization’s intranet that is extended to users outside the organization, usually partners, vendors, and suppliers that are part of the organization.

An extranet provides access to needed services for external partners, without granting access to an organization’s entire network.


The Internet is a global system of interconnected computer networks that uses the standard TCP/IP to link several billion devices all over the world. Simply defined, the Internet is a ‘network of networks that consists of billions of private, public, academic, business, and government networks.

These networks can be of local to global scope that is linked by various networking technologies be it electronic, wireless, or optical. Every computer on the internet is identified by a unique address called its IP address.

An IP address is a unique set of numbers (such as that identifies a computer`s physical location. The Internet also carries an extensive range of information resources and services, such as inter-linked hypertext documents and the World Wide Web (www), support for email, etc. The Internet is accessible to every user all over the world.

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