Computer Networks

Computer Networks

Introduction to Computer Networks

1. Data Communications

Data Communication refers to the exchange of data (in the form of bits) between two or more devices (computers, mobile phones, etc.) using a transmission medium such as cables or wireless signals. It is successful only when the data sent is correctly received and understood by the receiver.

Components of Data Communication

There are five essential components involved in any data communication system:

Component	Description
1. Message	The data or information to be communicated (text, audio, video, images, etc.)
2. Sender	The device or person that initiates the message (e.g., computer, mobile phone)
3. Receiver	The device or person that receives the message (e.g., another computer, printer)
4. Medium	The physical path through which the message travels (e.g., copper wire, fiber optics, air)
5. Protocol	A set of rules that governs how data is transmitted (e.g., TCP/IP, HTTP, FTP)

Characteristics of Data Communication

To ensure effective and efficient communication, the following characteristics are important:

Characteristic	Description
1. Delivery	Data must reach the correct destination (receiver).
2. Accuracy	Data must be delivered correctly, without any errors.
3. Timeliness	Data must be delivered on time, especially in real-time systems (e.g., video calls).
4. Jitter	Refers to the variation in packet arrival time; should be minimized in audio/video streaming.

Example in Real Life:

WhatsApp message:

Sender: Your phone
Receiver: Friend’s phone
Message: Text or image you send
Medium: Mobile network or Wi-Fi
Protocol: Internet protocols (TCP/IP, HTTP)

Concept	Key Points
Definition	Exchange of data via transmission medium
Components	Message, Sender, Receiver, Medium, Protocol
Characteristics	Delivery, Accuracy, Timeliness, Jitter

2. Networks

Definition of a Network

A network is a collection of devices (also called nodes, such as computers, printers, mobile phones, etc.) that are connected through communication links (wired or wireless) to share information and resources. A communication link can be physical (like cables) or wireless (like radio waves).

Common Examples of Networks

· Your home Wi-Fi network (router connected to phones, laptops, etc.)

· A college campus LAN

· The Internet, the largest network in the world

Goals of Computer Networks

Goal	Description
1. Resource Sharing	Enables multiple users to share devices (like printers, files, software, etc.) connected to the network.
2. High Reliability	If one path or device fails, the network can reroute data through another path (fault tolerance).
3. Cost-effective Communication	Reduces cost by allowing users to communicate over the network instead of physical travel (e.g., emails, video calls).
4. Scalability and Expandability	Networks can be easily expanded by adding new devices without changing the entire system.

Key Terms

· Node: Any device connected to the network (e.g., PC, router, switch)

· Link: The connection between two devices (wired or wireless)

· Topology: The layout of how nodes are connected (e.g., star, bus, ring)

Summary Box

Term	Explanation
Network	A group of connected devices that communicate and share resources
Goals	Resource sharing, high reliability, cost-effectiveness, scalability

Example:

In a college lab, students’ computers are connected via a LAN to a central printer and file server. This allows sharing of files and printers, ensuring low cost and high productivity.

Bus Topology

Features:

· Single central cable (bus)

· Data travels in both directions

· Terminators at ends

Star Topology

Features:

· Central hub/switch connects all nodes

· Easy to manage, but hub failure = entire network failure

Ring Topology

Features:

· Devices form a closed loop

· Data travels in one or both directions (depending on type – single / dual )

· Token Ring is an example

Mesh Topology

Features:

· Every device connects to every other device

· Very reliable but expensive and complex

Tree Topology (Hierarchical)

Features:

· Combination of star + bus

· Suitable for scalable and structured networks (e.g., enterprise)

Hybrid Topology

· A mix of two or more topologies (e.g., Star-Bus, Star-Ring)

Topology Advantages and Drawbacks

Topology	Key Advantage	Major Drawback
Bus	Easy to implement	Break in backbone = failure
Star	Easy to manage	Hub failure = network down
Ring	Predictable performance	Failure of one affects all
Mesh	High reliability	Expensive, complex wiring
Tree	Scalable	Root hub failure = failure
Hybrid	Flexible	Complex design and management

3. Network Types

PAN (Personal Area Network): e.g., Bluetooth, USB
LAN (Local Area Network): Small geographical area (e.g., home, office)
MAN (Metropolitan Area Network): Covers city (e.g., cable TV networks)
WAN (Wide Area Network): Covers large geographical areas (e.g., Internet)
CAN (Campus Area Network) and SAN (Storage Area Network) are other specific types

4. Internet History

1960s: ARPANET project funded by the U.S. DoD
1970s: Development of TCP/IP
1983: ARPANET adopts TCP/IP
1990s: World Wide Web (WWW) by Tim Berners-Lee
2000s: Internet expands to mobile and IoT

5. Standards and Administration

Standards: Ensure interoperability between devices and protocols

IEEE (e.g., IEEE 802.3 for Ethernet)
IETF (develops Internet standards like TCP/IP)
ISO, ITU-T, ANSI, W3C

Administration:

ICANN (Internet Corporation for Assigned Names and Numbers) – IP address and domain name management
IANA (Internet Assigned Numbers Authority) – Allocates IP addresses and protocol parameters

6. Network Models

a. Protocol Layering:

Concept of dividing communication tasks into layers, each responsible for a part of the process.

b. TCP/IP Protocol Suite (DoD Model):

5 Layers:

Application
Transport
Internet
Network Access
Physical Layer

What is the TCP/IP model and how it works?

PopularProtocols:
HTTP, FTP, TCP, IP, DNS, DHCP, etc.

c. OSI Model (Open Systems Interconnection):

7 Layers: Please Do Not Touch Steve’s Pet Alligator

Physical
Data Link
Network
Transport
Session
Presentation
Application

7. Transmission Media

Guided Media (Wired):

Twisted Pair
Coaxial Cable
Fiber Optic Cable

Unguided Media (Wireless):

Radio waves
Microwaves
Infrared

Twisted Pair

A Twisted-pair cable is a cable made by intertwining two separate insulated wires. There are two twisted pair types: shielded and unshielded. A STP (Shielded Twisted-Pair) cable has a fine wire mesh surrounding the wires to protect the transmission and a UTP (Unshielded Twisted Pair) cable does not. Shielded cable is used in older telephone networks and network and data communications to reduce outside interference. The illustration gives an example of how the inside of these looks. Short for Unshielded Twisted Pair, a UTP cable is a cable used in computer networking that consists of two shielded wires twisted around each other. As the name would imply, these cables do not have insulation (shielding) between each of the paired wires. Consequently, they do not block electromagnetic interference, resulting in a higher risk of packet loss or corruption. Short for Shielded Twisted-Pair cable, a STP cable was developed by IBM for Token Ring networks. It consists of two individual wires wrapped in a foil shielding that helps provide more reliable data transmission.

Coaxial Cable

Coaxial cable, can also be called "coax," is a type of shielded cable used in computer networks to transmit high-frequency signals. It features a central conductor, an insulator, a metallic shield, and an outer jacket, providing resistance to electromagnetic interference (EMI) and enabling longer cable runs compared to other types like twisted pair. Coaxial cables are frequently used in applications like cable television, broadband internet, and some older network setups. Different types of coaxial cables exist, such as RG-59 (used for cable TV and short network runs) and RG-6 (commonly used for cable internet). Coaxial cables are used for various purposes, including:

· Cable TV and Internet: Delivering signals to homes and businesses.

· Older Networks: Some older network topologies (like 10BASE5 and 10BASE2) used coaxial cable for connections.

· Other Applications: Connecting radio transmitters and receivers to antennas, and in some data buses.

Advantages:

· The shielding minimizes noise and interference, ensuring reliable signal transmission.

· Can transmit signals over greater distances than some other cable types.

Disadvantages:

· Can experience signal degradation over very long distances.

· Offers lower bandwidth compared to fiber optic cables.

· While easier than some older technologies, it's generally not as simple to install as twisted pair.

Optical Fiber Cable (OFC)

Optical fiber cables are for high-speed, and to cover long-distance data transmission in computer networks. They utilize light pulses to carry data through thin strands of glass or plastic, offering significant advantages over traditional copper cables. These advantages include higher bandwidth, lower signal degradation, and immunity to electromagnetic interference.

· Light-based transmission: Unlike electrical signals in copper cables, optical fiber uses light pulses to transmit data.

· Core and cladding: The core, a thin strand of glass or plastic, carries the light, while the cladding reflects the light back into the core, preventing signal loss.

· Protection: The core and cladding are surrounded by a protective layer called the buffer, and then a jacket for further protection.

Advantages

Higher Bandwidth:

Optical fibers can carry significantly more data than copper cables, enabling faster internet speeds and supporting high-bandwidth applications.

Longer Distance:

Signals can travel much farther with optical fiber before needing amplification, making it ideal for large networks and long-distance communication.

Reduced Signal Degradation:

Optical fiber experiences less signal loss (attenuation) over distance compared to copper, ensuring reliable data transmission.

Immunity to Interference:

Unlike copper cables, optical fiber is not susceptible to electromagnetic interference (EMI) or radio frequency interference (RFI), ensuring a clean and reliable signal.

Security:

Fiber optic cables are difficult to tap without detection, and breaking the cable disrupts the signal, enhancing security.

Smaller and Lighter:

Fiber optic cables are typically smaller and lighter than copper cables, making them easier to install and manage.

Types of Optical Fiber Cables:

Single-mode fiber: Used for long distances and high bandwidth applications.
Multimode fiber: Used for shorter distances and less demanding applications.

Challenges:

High Cost:

While the cost of fiber optic cables has decreased, they can still be more expensive than copper cables, particularly for short distances.

Installation:

Fiber optic cables require specialized tools and techniques for installation and splicing, which can increase installation costs.

Brittle:

Fiber optic cables are more fragile than copper cables and can be damaged by bending or pulling during installation.

Unguided or Wireless Transmission Media

Unguided media, also termed as unbound transmission medium, is a method of transmitting data without the need for cables. Physical geography has no bearing on these media. Unguided media are also known as wireless communication. It is a wireless transmission media channel that does not need a physical medium to connect to network nodes or servers.

There are three types of unguided Transmission Media, that are:

Radio Waves
Microwave
Infrared

Let’s understand each in detail.

Radio Waves Transmission

Radio waves are a type of non-ionizing electromagnetic radiation used for wireless communication. Let’s understand in detail.

Frequency Range

Radio waves have a frequency range of 3 kHz to 300 GHz.
It is important to note that lower-frequency radio waves are mainly used for AM radio broadcasting. On the other hand, higher frequency radio waves are used for FM radio broadcasting as well as for satellite communications.

Direction of Communication

Radio waves can be directional, which means that the waves are focused in a specific direction. Also, radio waves can be omnidirectional, i.e., propagated in all directions.

Role of Antenna

An antenna is a crucial component of radio wave transmission, which is responsible for converting electrical energy into radio waves.

The antenna’s shape, size, and orientation affect the direction and strength of the radio waves.

Application

Radio broadcasting
Mobile communication
Wireless networking
Radar and navigation

Advantages of Radio Waves

Long-distance Communication
Portable
Reliable Communication
Easy Installation

Disadvantages of Radio Waves

Prone to Interference
Atmospheric Disturbances
Limited Bandwidth
Health Risks

Microwave Transmission

Microwave transmission is a method of transmitting data through high-frequency electromagnetic waves over long distances. Let’s understand in detail.

Frequency Range

Microwaves generally operate at a frequency range of 1GHz to 300 GHz.
It is important to note that the most common frequency range is between 3GHz to 30 GHz.

Direction of Communication

Microwaves are line-of-sight (LOS) communications. It simply means that the transmitting and receiving antennas must be in direct sight of each other.
Microwaves are Unidirectional.

Role of Antenna

The antenna plays a crucial role in microwave transmission, as it converts electrical signals into microwave energy and transmits them through the air.

Types of Microwave Transmission

There are two types of microwave transmission. These are:

Terrestrial Microwaves: These microwaves are used for communication purposes, especially between two points on the Earth’s surface. One such example is the communication between two towers or buildings.

Satellite Microwaves: These microwaves are used for communication between the Earth and a satellite in orbit. It is crucial for global communication and broadcasting.

Applications of Microwave Transmission

Wireless local area networks (WLANs)
Satellite communications
Radar systems
Wireless broadband internet
Point-to-point communication links
Radio astronomy
Military communications
Weather radar systems

Advantages of Microwave Transmission

High-speed data transfer
Easy to install and set up
Cost-effective solutions
Reliable communication with minimal downtime
Fast deployment

Disadvantages of Microwave Transmission

Interrupted by physical obstacles
Obstructions in the line of sight can affect signal quality
Security risks
Limited range
Atmospheric conditions can impact microwave signal quality

Infrared

Infrared waves are a type of energy that can travel through the air. Let’s discuss Infrared waves in detail.

Frequency Range – The frequency range is between 300GHz and 400 THz. This simply means that they can travel a certain distance and then fade away.

Communication Range – In general, Infrared waves are used to send information between devices that are close to each other. This is known as short-range communication.

How it works?

In order to send information with Infrared waves, we need special devices known as transceivers. These devices can send as well as receive infrared light. For infrared communication to work, it is recommended that the two devices that need to communicate with one another should be in sight of each other. In simple words, they need to be facing each other. If not, the light can bounce off a light-colored surface like a ceiling or a wall in order to reach the other device.

Applications

Wireless Keyboards and Mouse
TV Remote Control
Night Vision
Weapon System

Advantages of Infrared

Secure and high-speed data transfer
Low Power Consumption
Relatively directional
Easy to Build into Devices

Disadvantages of Infrared

Line of Sight Requirement
Limited Range
High Attenuation

That’s all from the Wireless Transmission Media.

Comparison of Various Transmission Media

Transmission Media	Speed	Distance	Interference Resistance	Cost	Best Use Cases
Twisted Pair Cable	Up to 10 Gbps	100 Meter	Moderate	Low	LAN, Telephone Lines
Coaxial Cable	Up to 10 Gbps	Several KM	High	Medium	Cable TV, Broadband
Fiber Optic Cable	Up to Tbps	Several KM	Very High	High	High-speed Internet
Radio Waves	Up to Gbps	Several KM	Low	Medium	Wi-Fi, Mobile Networks
Microwaves	Up to Gbps	100+ KM	Medium	High	Satellite, TV Broadcasting
Infrared	Mbps	Few Meters	Very High	Low	Remote Controls, Bluetooth

How to choose the right Transmission Media?

Effective communication is more important to choose the right transmission media. Let us discuss some of the factors that need to be considered.

Distance: It simply means the distance the signal needs to travel. For short distances, twisted pair or fiber optic cables may be suitable. For longer distances, coaxial cables or satellite transmission is suitable.
Bandwidth: It means the amount of data to be transmitted. Low-bandwidth applications such as voice calls can use twisted pair cables. At the same time, high-bandwidth applications such as video streaming require fibre optics or coaxial cables.
Cost: It is crucial to consider the cost factor while choosing the transmission media. If someone wants to go for a cheaper option, twisted pair cables are the best option to go.
Security: It is always good to secure your network in order to protect sensitive information as well as resources. For example, fiber optic cables are often used for high-security applications.

What are the causes of Transmission Impairment?

Transmission impairment refers to the degradation or weakening of signals as they travel from the sender to the receiver. This can happen in various communication systems, such as phone networks, internet connections, and many others.

Below, we have pointed out some of the common causes of transmission impairment.

Attenuation by Physical Barriers
Interference from Other Signals
Equipment Failure or Malfunction
Environmental Factors
Bandwidth Limitations
Signal Compression
Digital Signal Processing Errors

Comparing Guided and Unguided Transmission Media

Factor	Guided Media	Unguided Media
Transmission Medium	Physical Cables (Copper, Fiber Optics)	Air, Space
Cost	Lower for low disances	Very High
Distance	Short to medium	Long
Interference	Very low	High interference
Speed	High, especially with Fiber Optics Cable	Varies from low to high depending on the technology
Flexibility	Very less flexible due to fixed infrastructure	Highly Flexible

8. Switching

Switching is the process of transferring data packets from one device to another in a network, or from one network to another, using specific devices called switches. A computer user experiences switching all the time for example, accessing the Internet from your computer device, whenever a user requests a webpage to open, the request is processed through switching of data packets only.

Switching takes place at the Data Link layer of the OSI Model. This means that after the generation of data packets in the Physical Layer, switching is the immediate next process in data communication.

Switch

· A switch is a hardware device in a network that connects and helps multiple devices share a network without their data interfering with each other.

· A switch works like a traffic cop at a busy intersection. When a data packet arrives, the switch decides where it needs to go and sends it through the right port.

· Some data packets come from devices directly connected to the switch, like computers or VoIP phones. Other packets come from devices connected through hubs or routers.

· The switch knows which devices are connected to it and can send data directly between them. If the data needs to go to another network, the switch sends it to a router, which forwards it to the correct destination.

Switching methods:

Techniques to route data between source and destination:

· Frame Reception: The switch receives a data frame or packet from a computer connected to its ports.

· MAC Address Extraction: The switch reads the header of the data frame and collects the destination MAC Address from it.

· MAC Address Table Lookup: Once the switch has retrieved the MAC Address, it performs a lookup in its Switching table to find a port that leads to the MAC Address of the data frame.

· Forwarding Decision and Switching Table Update: If the switch matches the destination MAC Address of the frame to the MAC address in its switching table, it forwards the data frame to the respective port. However, if the destination MAC Address does not exist in its forwarding table, it follows the flooding process, in which it sends the data frame to all its ports except the one it came from and records all the MAC Addresses to which the frame was delivered. This way, the switch finds the new MAC Address and updates its forwarding table.

· Frame Transition: Once the destination port is found, the switch sends the data frame to that port and forwards it to its target computer/network.

Circuit Switching: In this type of switching, a connection is established between the source and destination beforehand. This connection receives the complete bandwidth of the network until the data is transferred completely.
This approach is better than message switching as it does not involve sending data to the entire network, instead of its destination only.

Dedicated path established (e.g., telephone networks)

Packet Switching: This technique requires the data to be broken down into smaller components, data frames, or packets. These data frames are then transferred to their destinations according to the available resources in the network at a particular time.
This switching type is used in modern computers and even the Internet. Here, each data frame contains additional information about the destination and other information required for proper transfer through network components.

Data broken into packets (e.g., Internet)

Message Switching: This is an older switching technique that has become obsolete. In message switching technique, the entire data block/message is forwarded across the entire network thus, making it highly inefficient.

Entire message sent to intermediate nodes

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