computer networks study notes, Study notes of Computer Networks

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CN_KCS-603 Lecture-

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What is a Computer Network?

• A network is a set of devices (often referred to as nodes) connected by communication links.
• A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.
• “Computer network’’ to mean a collection of autonomous computers interconnected by a single technology. Two computers are said to be interconnected if they are able to exchange information.
• The connection need not be via a copper wire; fiber optics, microwaves, infrared, and communication satellites can also be used.
• Networks come in many sizes, shapes and forms, as we will see later. They are usually connected together to make larger networks, with the Internet being the most well- known example of a network of networks.

Components of Computer Network:

A data communications system has five components

• Message: The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video.
• Sender: The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on.
• Receiver: The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.
• Transmission medium: The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
• Protocol: A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.

Uses Of Computer Network

Resource sharing: Resource sharing is the sharing of resources such as programs, printers, and data among the users on the network without the requirement of the physical location of the resource and user.

Server-Client model: Computer networking is used in the server-client model. A server is a central computer used to store the information and maintained by the system administrator. Clients are the machines used to access the information stored in the server remotely.

Communication medium: Computer network behaves as a communication medium among the users. For example, a company contains more than one computer has an email system which the employees use for daily communication.

E-commerce: Computer network is also important in businesses. We can do the business over the internet. For example, amazon.com is doing their business over the internet, i.e., they are doing their business over the internet.

Some of the network applications in different fields are the following.

1. Marketing and sales Computer Network
   2. Financial services
2. Manufacturing. CAD, CAM etc.
   4. Information services
3. Cellular telephone
4. Cable television
5. Teleconferencing
   8. EDI
6. E-mail etc.

Data Representation

• Text (ASCII)
• Images (Pixel)
• Numbers
• Audio Bit Pattern
• Video

Data Flow

• Simplex: In simplex mode, the communication is unidirectional, as on a one way street. Only one of the two devices on a link can transmit; the other can only receive (Figure a). Keyboards and traditional monitors are examples of simplex devices
• Half-Duplex: In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa (Figure b). Walkie-talkies and CB (citizens band) radios are both halfduplex systems.
• Full-Duplex :

In full-duplex, both stations can transmit and receive simultaneously (Figure c). One common example of full-duplex communication is the telephone network. When two people are communicating by a telephone line, both can talk and listen at the same time. The full-duplex mode is used when communication in both directions is required all the time.

Multipoint:

• A multipoint (also called multi-drop) connection is one in which more than two specific devices share a single link In a multipoint environment, the capacity of the channel is shared, either spatially or temporally.
• If several devices can use the link simultaneously, it is a spatially shared connection.
• If users must take turns, it is a timeshared connection.

Physical Topology:

• The term physical topology refers to the way in which a network is laid out physically.
• Two or more devices connect to a link; two or more links form a topology.
• The topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another.

MESH TOPOLOGY:

 A mesh topology is the one where every node is connected to every other node in the network.

 A mesh topology can be a full mesh topology or a partially connected mesh topology.  In a full mesh topology, every computer in the network has a connection to each of the other computers in that network.  The number of connections in this network can be calculated using the following formula (n is the number of computers in the network): n(n-1)/2 In a partially connected mesh topology, at least two of the computers in the network have connections to multiple other computers in that network.  It is an inexpensive way to implement redundancy in a network. In the event that one of the primary computers or connections in the network fails, the rest of the network continues to operate normally. Advantages of a mesh topology

• Can handle high amounts of traffic, because multiple devices can transmit data simultaneously.
• A failure of one device does not cause a break in the network or transmission of data.
• Adding additional devices does not disrupt data transmission between other devices. Disadvantages of a mesh topology
• The cost to implement is higher than other network topologies, making it a less desirable option.
• Building and maintaining the topology is difficult and time consuming.
• The chance of redundant connections is high, which adds to the high costs and potential for reduced efficiency.

BUS TOPOLOGY

• A line topology, a bus topology is a network setup in which each computer and network device are connected to a single cable or backbone.

Advantages of bus topology

• It works well when you have a small network.
• It's the easiest network topology for connecting computers or peripherals in a linear fashion.
• It requires less cable length than a star topology Disadvantages of bus topology
• It can be difficult to identify the problems if the whole network goes down.
• It can be hard to troubleshoot individual device issues. · Bus topology is not great for large networks.
• Terminators are required for both ends of the main cable.
• Additional devices slow the network down.
• If a main cable is damaged, the network fails or splits into two.

RING TOPOLOGY

• A ring topology is a network configuration in which device connections create a circular data path.
• In a ring network, packets of data travel from one device to the next until they reach their destination.
• Most ring topologies allow packets to travel only in one direction, called a unidirectional ring network. Others permit data to move in either direction, called bidirectional.
• The major disadvantage of a ring topology is that if any individual connection in the ring is broken, the entire network is affected.
• Ring topologies may be used in either local area networks (LANs) or wide area networks (WANs).

Advantages of ring topology

• All data flows in one direction, reducing the chance of packet collisions.
• A network server is not needed to control network connectivity between each workstation.
• Data can transfer between workstations at high speeds.
• Additional workstations can be added without impacting performance of the network.

Disadvantages of Ring Topology

• All data being transferred over the network must pass through each workstation on the network, which can make it slower than a star topology.
• The entire network will be impacted if one workstation shuts down.
• The hardware needed to connect each workstation to the network is more expensive than Ethernet cards and hubs/switches.

Computer Network Types / Categories of networks

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 four types :

o LAN(Local Area Network) o PAN(Personal Area Network) o MAN(Metropolitan Area Network) o 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.

 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.

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:

o Mobile Broadband: A 4G network is widely used across a region or country. o 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. o 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:

 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. 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.