BASIC COMPUTER NETWORK

Computer Network: 

An interconnection of multiple devices, also known as hosts, that are connected using multiple paths for the purpose of sending/receiving data or media. Computer networks can also include multiple devices/mediums which help in the communication between two different devices; these are known as Network devices and include things such as routers, switches, hubs, and bridges

Open system: 

A system which is connected to the network and is ready for communication. 

Closed system: 

A system which is not connected to the network and can’t be communicated with. 

Computer networks share common devices, functions, and features including servers, clients, transmission media, shared data, shared printers and other hardware and software resources, network interface card(NIC), local operating system(LOS), and the network operating system (NOS)

TYPES OF COMPUTER NETWORKS

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 four types:

  1. Local Area Network (LAN)
  2. Metropolitan Area Network (MAN)
  3. Wide Area Network (WAN)
  4. Personal Area Network (PAN)

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.
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.
  • The most widely used protocols in MAN are RS-232, Frame Relay, ATM, ISDN, OC-3, ADSL, etc.
  • It has a higher range than Local Area Network(LAN).
Uses Of Metropolitan Area Network
  • MAN is used in communication between the banks in a city.
  • It can be used in an Airline Reservation.
  • It can be used in a college within a city.
  • It can also be used for communication in the military.
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, fibre optic cable or satellite links.
  • The internet is one of the biggest WAN in the world.
  • A Wide Area Network is widely used in the field of Business, government, and education.
Examples Of Wide Area Network:
  • Mobile Broadband: A 4G network is widely used across a region or country.
  • Last mile: A telecom company is used to provide the internet services to the customers in hundreds of cities by connecting their home with fiber.
  • Private network: A bank provides a private network that connects the 44 offices. This network is made by using the telephone leased line provided by the telecom company
Advantages Of Wide Area Network

Following are the advantages of the Wide Area Network:

  1. Geographical area: A Wide Area Network provides a large geographical area. Suppose if the branch of our office is in a different city then we can connect with them through WAN. The internet provides a leased line through which we can connect with another branch.
  2. Centralized data: In case of WAN network, data is centralized. Therefore, we do not need to buy the emails, files or back up servers.
  3. Get updated files: Software companies work on the live server. Therefore, the programmers get the updated files within seconds.
  4. Exchange messages: In a WAN network, messages are transmitted fast. The web application like Facebook, Whatsapp, Skype allows you to communicate with friends.
  5. Sharing of software and resources: In WAN network, we can share the software and other resources like a hard drive, RAM.
  6. Global business: We can do the business over the internet globally.
  7. High bandwidth: If we use the leased lines for our company then this gives the high bandwidth. The high bandwidth increases the data transfer rate which in turn increases the productivity of our company.

Disadvantages of Wide Area Network:

The following are the disadvantages of the Wide Area Network:

  1. Security issue: A WAN network has more security issues as compared to LAN and MAN network as all the technologies are combined together that creates the security problem.
  2. Needs Firewall & antivirus software: The data is transferred on the internet which can be changed or hacked by the hackers, so the firewall needs to be used. Some people can inject the virus in our system so antivirus is needed to protect from such a virus.
  3. High Setup cost: An installation cost of the WAN network is high as it involves the purchasing of routers, switches.
  4. Troubleshooting problems: It covers a large area so fixing the problem is difficult.
PAN(Personal Area Network

Personal Area Network is a network arranged within an individual person, typically within a range of 10 meters.
Personal Area Network is used for connecting the computer devices of personal use is known as Personal Area Network.
  • Thomas Zimmerman was the first research scientist to bring the idea of the Personal Area Network.
  • Personal Area Network covers an area of 30 feet.
  • Personal computer devices that are used to develop the personal area network are the laptop, mobile phones, media player and play stations
There are two types of Personal Area Network:
  1. Wired Personal Area Network
  2. Wireless Personal Area Network
Wireless Personal Area Network: Wireless Personal Area Network is developed by simply using wireless technologies such as WiFi, Bluetooth. It is a low range network.

Wired Personal Area Network: Wired Personal Area Network is created by using the USB.

Examples Of Personal Area Network

  1. Body Area Network: Body Area Network is a network that moves with a person. For example, a mobile network moves with a person. Suppose a person establishes a network connection and then creates a connection with another device to share the information.
  2. Offline Network: An offline network can be created inside the home, so it is also known as a home network. A home network is designed to integrate the devices such as printers, computer, television but they are not connected to the internet.
  3. Small Home Office: It is used to connect a variety of devices to the internet and to a corporate network using a VPN
Internetwork
An internetwork is defined as two or more computer network LANs or WAN or computer network segments are connected using devices, and they are configured by a local addressing scheme. This process is known as internetworking.
  • An interconnection between public, private, commercial, industrial, or government computer networks can also be defined as internetworking.
  • An internetworking uses the internet protocol.
  • The reference model used for internetworking is Open System Interconnection(OSI).

Types Of Internetwork:
1. Extranet: 
An extranet is a communication network based on the internet protocol such as Transmission Control protocol and internet protocol. It is used for information sharing. The access to the extranet is restricted to only those users who have login credentials. An extranet is the lowest level of internetworking. It can be categorized as MAN, WAN or other computer networks. An extranet cannot have a single LAN, atleast it must have one connection to the external network.

2. Intranet:
 An intranet is a private network based on the internet protocol such as Transmission Control protocol and internet protocol. An intranet belongs to an organization which is only accessible by the organization's employee or members. The main aim of the intranet is to share the information and resources among the organization employees. An intranet provides the facility to work in groups and for teleconferences.

Intranet advantages:
  • Communication: It provides a cheap and easy communication. An employee of the organization can communicate with another employee through email, chat.
  • Time-saving: Information on the intranet is shared in real time, so it is time-saving.
  • Collaboration: Collaboration is one of the most important advantage of the intranet. The information is distributed among the employees of the organization and can only be accessed by the authorized user.
  • Platform independency: It is a neutral architecture as the computer can be connected to another device with different architecture.
  • Cost effective: People can see the data and documents by using the browser and distributes the duplicate copies over the intranet. This leads to a reduction in the cost

Network devices
Network devices, or networking hardware, are physical devices that are required for communication and interaction between hardware on a computer network.

Types of network devices
Here is the common network device list:
  1. Hub
  2. Switch
  3. Router
  4. Bridge
  5. Gateway
  6. Modem
  7. Repeater
  8. Access Point
Hub
Hubs connect multiple computer networking devices together. A hub also acts as a repeater in that it amplifies signals that deteriorate after traveling long distances over connecting cables.

A hub is the simplest in the family of network connecting devices because it connects LAN components with identical protocols

Switch
Switches generally have a more intelligent role than hubs. A switch is a multiport device that improves network efficiency. The switch maintains limited routing information about nodes in the internal network, and it allows connections to systems like hubs or routers.


Strands of LANs are usually connected using switches. Generally, switches can read the hardware addresses of incoming packets to transmit them to the appropriate destination

Router
Routers help transmit packets to their destinations by charting a path through the sea of interconnected networking devices using different network topologies. Routers are intelligent devices, and they store information about the networks they’re connected to. Most routers can be configured to operate as packet-filtering firewalls and use access control lists (ACLs). 


Routers, in conjunction with a channel service unit/data service unit (CSU/DSU), are also used to translate from LAN framing to WAN framing. This is needed because LANs and WANs use different network protocols. Such routers are known as border routers. They serve as the outside connection of a LAN to a WAN, and they operate at the border of your network

Bridge
Bridges are used to connect two or more hosts or network segments together. The basic role of bridges in network architecture is storing and forwarding frames between the different segments that the bridge connects.
They use hardware Media Access Control (MAC) addresses for transferring frames. By looking at the MAC address of the devices connected to each segment, bridges can forward the data or block it from crossing. Bridges can also be used to connect two physical LANs into a larger logical LAN.

Gateway
Gateways normally work at the Transport and Session layers of the OSI model. At the Transport layer and above, there are numerous protocols and standards from different vendors; gateways are used to deal with them. Gateways provide translation between networking technologies such as Open System Interconnection (OSI) and Transmission Control Protocol/Internet Protocol (TCP/IP). 

Because of this, gateways connect two or more autonomous networks, each with its own routing algorithms, protocols, topology, domain name service, and network administration procedures and policies.

Modem
Modems (modulators-demodulators) are used to transmit digital signals over analog telephone lines. Thus, digital signals are converted by the modem into analog signals of different frequencies and transmitted to a modem at the receiving location. 


The receiving modem performs the reverse transformation and provides a digital output to a device connected to a modem, usually a computer. The digital data is usually transferred to or from the modem over a serial line through an industry standard interface, RS-232.

Repeater
A repeater is an electronic device that amplifies the signal it receives. You can think of repeater as a device which receives a signal and retransmits it at a higher level or higher power so that the signal can cover longer distances, more than 100 meters for standard LAN cables. Repeaters work on the Physical layer.



Access Point
While an access point (AP) can technically involve either a wired or wireless connection, it commonly means a wireless device. An AP works at the second OSI layer, the Data Link layer, and it can operate either as a bridge connecting a standard wired network to wireless devices or as a router passing data transmissions from one access point to another
TOPOLOGY NETWORK
Topology is derived from two Greek words topo and logy, where topo means 'place' and logy means 'study'. 
In computer networks, a topology is used to explain how a network is physically connected and the logical flow of information in the network. 
A topology mainly describes how devices are connected and interact with each other using communication links.

In computer networks, there are mainly two types of topologies, they are:
1. Physical Topology: 
A physical topology describes the way in which the computers or nodes are connected with each other in a computer network. It is the arrangement of various elements(link, nodes, etc.), including the device location and code installation of a computer network. In other words, we can say that it is the physical layout of nodes, workstations, and cables in the network.
2. Logical Topology:
A logical topology describes the way, data flow from one computer to another. It is bound to a network protocol and defines how data is moved throughout the network and which path it takes. In other words, it is the way in which the devices communicate internally.
Network topology defines the layout, virtual shape, or structure of the network, not only physically but also logically. A network can have one physical topology and multiple logical topologies at the same time.

In this article, we will mainly concentrate on physical topologies. We'll learn about different types of physical topologies, their advantages, and disadvantages.

In a computer network, there are mainly six types of physical topology, they are:
  1. Bus Topology
  2. Ring Topology
  3. Star Topology
  4. Mesh Topology
  5. Tree Topology
  6. Hybrid Topology
Bus Topology
Bus topology is the simplest kind of topology in which a common bus or channel is used for communication in the network. The bus is connected to various taps and droplines. Taps are the connectors, while droplines are the cables connecting the bus with the computer. In other words, there is only a single transmission line for all nodes.
In this topology, the bus acts as the backbone of the network, which joins every computer and peripherals in the network. Both ends of the shared channel have line terminators. The data is sent only in one direction and as soon as it reaches the end, the terminator removes the data from the communication line(to prevent signal bounce and data flow disruption)
Advantages of Bus topology:
  • Low-cost cable: In bus topology, nodes are directly connected to the cable without passing through a hub. Therefore, the initial cost of installation is low.
  • Moderate data speeds: Coaxial or twisted pair cables are mainly used in bus-based networks that support upto 10 Mbps.
  • Familiar technology: Bus topology is a familiar technology as the installation and troubleshooting techniques are well known, and hardware components are easily available.
  • Limited failure: A failure in one node will not have any effect on other nodes.
Disadvantages of Bus topology:
  • Extensive cabling: A bus topology is quite simpler, but still it requires a lot of cabling.
  • Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes.
  • Signal interference: If two nodes send the messages simultaneously, then the signals of both the nodes collide with each other.
  • Reconfiguration difficult: Adding new devices to the network would slow down the network.
  • Attenuation: Attenuation is a loss of signal leads to communication issues. Repeaters are used to regenerate the signal.
Ring Topology
Ring topology is a topology in which each computer is connected to exactly two other computers to form the ring. The message passing is unidirectional and circular in nature


This network topology is deterministic in nature, i.e., each computer is given access for transmission at a fixed time interval. All the nodes are connected in a closed-loop. This topology mainly works on a token-based system and the token travels in a loop in one specific direction
Working of Token passing
  • A token moves around the network, and it is passed from computer to computer until it reaches the destination.
  • The sender modifies the token by putting the address along with the data.
  • The data is passed from one device to another device until the destination address matches. Once the token received by the destination device, then it sends the acknowledgment to the sender.
  • In a ring topology, a token is used as a carrier.
Advantages of Ring topology:
  • Network Management: Faulty devices can be removed from the network without bringing the network down.
  • Product availability: Many hardware and software tools for network operation and monitoring are available.
  • Cost: Twisted pair cabling is inexpensive and easily available. Therefore, the installation cost is very low.
  • Reliable: It is a more reliable network because the communication system is not dependent on the single host computer.
Disadvantages of Ring topology:
  • Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes.
  • Failure: The breakdown in one station leads to the failure of the overall network.
  • Reconfiguration difficult: Adding new devices to the network would slow down the network.
  • Delay: Communication delay is directly proportional to the number of nodes. Adding new devices increases the communication delay.
Star Topology
Star topology is a computer network topology in which all the nodes are connected to a centralized hub. The hub or switch acts as a middleware between the nodes. Any node requesting for service or providing service, first contact the hub for communication.
In a star topology, hub and switch act as a server, and the other connected devices act as clients. Only one input-output port and one cable are required to connect a node to the central device. This topology is better in terms of security because the data does not pass through every node
Advantages of Star topology
  • Efficient troubleshooting: Troubleshooting is quite efficient in a star topology as compared to bus topology. In a bus topology, the manager has to inspect the kilometers of cable. In a star topology, all the stations are connected to the centralized network. Therefore, the network administrator has to go to the single station to troubleshoot the problem.
  • Network control: Complex network control features can be easily implemented in the star topology. Any changes made in the star topology are automatically accommodated.
  • Limited failure: As each station is connected to the central hub with its own cable, therefore failure in one cable will not affect the entire network.
  • Familiar technology: Star topology is a familiar technology as its tools are cost-effective.
  • Easily expandable: It is easily expandable as new stations can be added to the open ports on the hub.
  • Cost effective: Star topology networks are cost-effective as it uses inexpensive coaxial cable.
  • High data speeds: It supports a bandwidth of approx 100Mbps. Ethernet 100BaseT is one of the most popular Star topology networks.
Disadvantages of Star topology
  • A Central point of failure: If the central hub or switch goes down, then all the connected nodes will not be able to communicate with each other.
  • Cable: Sometimes cable routing becomes difficult when a significant amount of routing is required.
Mesh Topology
Mesh topology is a computer network topology in which nodes are interconnected with each other. In other words, direct communication takes place between the nodes in the network.


There are mainly two types of Mesh:
  1. Full Mesh Topology: In a full mesh topology, each computer is connected to all the computers available in the network.
  2. Partial Mesh Topology: In a partial mesh topology, not all but certain computers are connected to those computers with which they communicate frequently.
Advantages of Mesh topology:
  • Reliable: The mesh topology networks are very reliable as if any link breakdown will not affect the communication between connected computers.
  • Fast Communication: Communication is very fast between the nodes.
  • Easier Reconfiguration: Adding new devices would not disrupt the communication between other devices.
Disadvantages of Mesh topology
  • Cost: A mesh topology contains a large number of connected devices such as a router and more transmission media than other topologies.
  • Management: Mesh topology networks are very large and very difficult to maintain and manage. If the network is not monitored carefully, then the communication link failure goes undetected.
  • Efficiency: In this topology, redundant connections are high that reduces the efficiency of the network.
Tree Topology:
Tree topology is a computer network topology in which all the nodes are directly or indirectly connected to the main bus cable. Tree topology is a combination of Bus and Star topology.

In a tree topology, the whole network is divided into segments, which can be easily managed and maintained. There is a main hub and all the other sub-hubs are connected to each other in this topology.
Advantages of Tree topology
  • Support for broadband transmission: Tree topology is mainly used to provide broadband transmission, i.e., signals are sent over long distances without being attenuated.
  • Easily expandable: We can add the new device to the existing network. Therefore, we can say that tree topology is easily expandable.
  • Easily manageable: In tree topology, the whole network is divided into segments known as star networks which can be easily managed and maintained.
  • Error detection: Error detection and error correction are very easy in a tree topology.
  • Limited failure: The breakdown in one station does not affect the entire network.
  • Point-to-point wiring: It has point-to-point wiring for individual segments.
Disadvantages of Tree topology
  • Difficult troubleshooting: If any fault occurs in the node, then it becomes difficult to troubleshoot the problem.
  • High cost: Devices required for broadband transmission are very costly.
  • Failure: A tree topology mainly relies on main bus cable and failure in main bus cable will damage the overall network.
  • Reconfiguration difficult: If new devices are added, then it becomes difficult to reconfigure.
Hybrid Topology:
A Hybrid topology is a computer topology which is a combination of two or more topologies. In practical use, they are the most widely used.
In this topology, all topologies are interconnected according to the needs to form a hybrid. All the good features of each topology can be used to make an efficient hybrid topology.


When two or more different topologies are combined together is termed as Hybrid topology and if similar topologies are connected with each other will not result in Hybrid topology. For example, if there exist a ring topology in one branch of ICICI bank and bus topology in another branch of ICICI bank, connecting these two topologies will result in Hybrid topology.
Advantages of Hybrid Topology
  • Reliable: If a fault occurs in any part of the network will not affect the functioning of the rest of the network.
  • Scalable: Size of the network can be easily expanded by adding new devices without affecting the functionality of the existing network.
  • Flexible: This topology is very flexible as it can be designed according to the requirements of the organization.
  • Effective: Hybrid topology is very effective as it can be designed in such a way that the strength of the network is maximized and weakness of the network is minimized.
Disadvantages of Hybrid topology
  • Complex design: The major drawback of the Hybrid topology is the design of the Hybrid network. It is very difficult to design the architecture of the Hybrid network.
  • Costly Hub: The Hubs used in the Hybrid topology are very expensive as these hubs are different from usual Hubs used in other topologies.
  • Costly infrastructure: The infrastructure cost is very high as a hybrid network requires a lot of cabling, network devices, etc.

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