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Basic of Computer Network

Computer Network

 Computer network

   - A computer network is a set of devices connected through links. A node can be       computer, printer, or any other device capable of sending or receiving the data. The       links connecting the nodes are known as communication channels.

   - network can be defined as a group of computers and other devices connected in   some  ways so as to be able to exchange data.

   - Each of the devices on the network can be thought of as a node; each node has a   unique address.

    - Addresses are numeric quantities that are easy for computers to work with, but not     for humans to remember.


Network Topology:

there are different types of topology are as follows

    1. Bus Topology

  • The bus topology is designed in such a way that all the stations are connected through a single cable known as a backbone cable.
  • Each node is either connected to the backbone cable by drop cable or directly connected to the backbone cable.
  • When a node wants to send a message over the network, it puts a message over the network. All the stations available in the network will receive the message whether it has been addressed or not.
  • The bus topology is mainly used in 802.3 (Ethernet) and 802.4 standard networks.
  • The configuration of a bus topology is quite simpler as compared to other topologies.

 Advantages of Bus topology:

  • Low-cost: In bus topology, nodes are directly connected to the cable without passing through a hub. Therefore, the initial cost of installation is low.
  • Easy Setup: the Bus topology is easy for setup
  • Moderate data speeds: Coaxial or twisted pair cables are mainly used in bus-based networks that support upto 10 Mbps.
  • Limited failure: A failure in one node will not have any effect on other nodes.
  • Familiar technology: Bus topology is a familiar technology as the installation and troubleshooting techniques are well known, and hardware components are easily available.

Disadvantages of Bus topology:

  • Extensive cabling: A bus topology is quite simpler, but still it requires a lot of cabling.
  • 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.

    2. Ring Topology

  • Ring topology is like a bus topology, but with connected ends.
  • The node that receives the message from the previous computer will retransmit to the next node.
  • The data flows in one direction, i.e., it is unidirectional.
  • The data flows in a single loop continuously known as an endless loop.
  • It has no terminated ends, i.e., each node is connected to other node and having no termination point.
  • The data in a ring topology flow in a clockwise direction.
  • The most common access method of the ring topology is token passing.

   Advantages of Ring topology:

  • 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.
  • Delay: Communication delay is directly proportional to the number of nodes. Adding new devices increases the communication delay.

    3. Star Topology

  • Star topology is an arrangement of the network in which every node is connected to the central hub, switch or a central computer.
  • The central computer is known as a server, and the peripheral devices attached to the server are known as clients.
  • Coaxial cable or RJ-45 cables are used to connect the computers.
  • Hubs or Switches are mainly used as connection devices in a .
  • Star topology is the most popular topology in network implementation.

Advantages of Star topology

  • 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.
  • 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.

    4. Tree topology

  • Tree topology combines the characteristics of bus topology and star topology.
  • A tree topology is a type of structure in which all the computers are connected with each other in hierarchical fashion.
  • The top-most node in tree topology is known as a root node, and all other nodes are the descendants of the root node.

Advantages of Tree topology

  • 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.

    5. Mesh topology

  • Mesh technology is an arrangement of the network in which computers are interconnected with each other through various redundant connections.
  • There are multiple paths from one computer to another computer.
  • It does not contain the switch, hub or any central computer which acts as a central point of communication.
  • The Internet is an example of the mesh topology.
  • Mesh topology is mainly used for WAN implementations where communication failures are a critical concern.
  • Mesh topology is mainly used for wireless networks.
  • Mesh topology can be formed by using the formula:
    Number of cables = (n*(n-1))/2;

There are Two Types of mesh Topology: -

1) Fully connected mesh topology

2) Partially connected mesh topology

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

  • 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.
  • Cost: A mesh topology contains a large number of connected devices such as a router and more transmission media than other topologies.


    6. Hybrid Topology

  • The combination of various different typologies is known as Hybrid topology.
  • A Hybrid topology is a connection between different links and nodes to transfer the data.
  • When two or more different typologies are combined together is termed as Hybrid topology and if similar typologies are connected with each other will not result in Hybrid topology. For example, if there exist a ring topology in one branch of State bank and bus topology in another branch of State bank, connecting these two typologies will result in Hybrid topology.

Advantages of Hybrid Topology

  • Scalable: Size of the network can be easily expanded by adding new devices without affecting the functionality of the existing network.
  • Reliable: If a fault occurs in any part of the network will not affect the functioning of the rest of the 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 typologies.
  • Costly infrastructure: The infrastructure cost is very high as a hybrid network requires a lot of cabling, network devices, etc.


An IP address identifies a host machine on the Internet.

-An IP port will identify a specific application running on an Internet host machine.

-A port is identified by a number, the port number.

-The number of ports is not functionally limited, in contrast to serial


 port numbers 






Port numbers
















20 and 21















SMTP (e-mail)








POP3 (e-mail)






















IP Address

IP address stands for internet protocol address it is an identifying number that is associated with a specific computer or computer network. When connected to the internet, the IP address allows the computers to send and receive information.


Working of  IP address-

An IP address allows computers to send and receive data over the internet. Most IP addresses are purely numerical, but as internet usage grows, letters have been added to some addresses.

There are four different types of IP addresses: public, private, static, and dynamic. While the public and private are indicative of the location of the network—private being used inside a network while the public is used outside of a network—static and dynamic indicate permanency.

A static IP address is one that was manually created, as opposed to having been assigned. A static address also does not change, whereas a dynamic IP address has been assigned by a Dynamic Host Configuration Protocol (DHCP) server and is subject to change. Dynamic IP addresses are the most common type of internet protocol addresses. Dynamic IP addresses are only active for a certain amount of time, after which they expire. The computer will either automatically request a new lease, or the computer may receive a new IP address.

Transmission Control Protocol (TCP)

-TCP provides by using IP packets a basic service that does guarantee safe delivery:

       error detection


       safe data transmission


       assurance that data are received in the correct order


User Datagram Protocol (UDP)

-Datagram protocol also built on top of IP.

-Has the same packet-size limit (64Kb) as IP, but allows for port number specification.

-Provides also 65,536 different ports.

-Hence, every machine has two sets of 65,536 ports: one for TCP and the other for UDP.

-Connectionless protocol, without any error detection facility.

-Provides only support for data transmission from one end to the other, without any further verification.

-The main interest of UDP is that since it does not make further verification, it is very fast.

-Useful for sending small size data in a repetitive way such as time information.

OSI (Open Systems Interconnection) Data Model

-ISO standard for computer networks design and functioning.

-Involves at least 7 layers, each playing a specific role when applications are communicating over the net.

-During the sending process, each layer (from top to down) will add a specific header to the raw data.

-At the reception, headers are eliminated conversely until the data arrived to the receiving application.

1) Physical layer: ensures a safe and efficient travel of data; consists of electronic circuits for data transmission etc.

2) Data link layer: in charge of data encapsulation under the form of packets and their interpretation at the physical layer.

3) Network layer: in charge of packets transmission from a source A to a destination B.

4) Transport layer: in charge of the delivery of packets from a source A to a destination B

5) Session layer: in charge of the management of network access.


6) Presentation layer: determines the format of the data transmitted to applications, data compressing/decompressing, encrypting etc.

7) Application layer: contains the applications which are used by the 

end-user, such as Java, Word etc.

The TCP/IP Model

-Consists of only 4 layers: 

1) application

2) transport

3) internet 

4) network

                                                                 TCP/IT LAYERS


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