Unit I: Introduction to Computer Network | CSE306: COMPUTER NETWORKS | B.Tech CSE

Unit I: Introduction to Computer Network

⭐Introduction

1. Network Software Architecture and its Layers and Protocols

Network Software Architecture

• Framework that defines how software components interact over a network.

Layered Network Model

• Network software architecture is generally structured in a layered model, where each layer performs a specific function. 
• The most commonly referenced model is the OSI (Open Systems Interconnection) Model and the TCP/IP Model.

• OSI Model (7 Layers)

• The OSI model consists of 7 layers. Each layer provides services to the layer above it and receives services from the layer below it. 
• Physical Layer, Data Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer, Application Layer.

• TCP/IP Model (4 Layers)

• The TCP/IP model is a simplified model primarily used in real-world networking and the internet. It has fewer layers than the OSI model.
• Network Interface Layer (Link Layer), Internet Layer, Transport Layer, Application Layer

Protocols

• Set of rules governing data communication.
• Importance:
• Ensure data integrity and efficient communication.
• Enable interoperability among different systems and devices.

• Ethernet: Standard for wired LAN communication.
• PPP: Used for direct communication between two network nodes.
• IP (Internet Protocol): The primary protocol for delivering packets across network boundaries.
• ICMP (Internet Control Message Protocol): Used for diagnostics (like ping).
• ARP: Translates IP addresses to MAC addresses for devices on the same local network.
• TCP (Transmission Control Protocol): Reliable, connection-oriented protocol ensuring data delivery.
• UDP (User Datagram Protocol): Connectionless protocol used for fast data transfer without error-checking.
• HTTP (Hypertext Transfer Protocol): Used for web browsing.
• HTTPS (Secure HTTP): Encrypts HTTP traffic to ensure secure communication.
• FTP (File Transfer Protocol): Used for file transfers.
• SMTP (Simple Mail Transfer Protocol): Used for sending emails.
• DNS (Domain Name System): Resolves domain names to IP addresses.

2. Network Hardware Architecture and its topologies and device like HUB, Switch and Routers

Network Hardware Architecture

• Network hardware architecture refers to the physical components involved in connecting devices and enabling communication between them.

Node

• any device or point in a network that can send, receive, or forward information.

Network Topologies

• Arrangement of different elements (links, nodes) in a network.

Types of Network Topologies

1. Star Topology:

   • All nodes connected to a central hub/switch.
   • Advantages: Easy to install and manage, failure of one node doesn’t affect others.

2. Bus Topology:

   • All devices share a single communication line (the bus).
   • Advantages: Simple layout, easy to set up.
   • Disadvantages: If the bus fails, the entire network goes down.

3. Ring Topology:

   • Each device is connected to two other devices, forming a ring.
   • Data travels in one direction.
   • Disadvantages: Failure of one device can disrupt the entire network.

4. Mesh Topology:

   • Each device is connected to multiple other devices.
   • Advantages: High redundancy and reliability.
   • Disadvantages: Complex installation and higher costs.

5. Hybrid Topology:

   • Combination of two or more topologies.
   • Advantages: Flexible and scalable.

Network Devices

1. HUB:

   • Simple device that connects multiple Ethernet devices.
   • Operates at the Physical Layer; broadcasts data to all ports.

2. Switch:

   • More intelligent than a hub; forwards data to specific devices based on MAC addresses.
   • Operates at the Data Link Layer; reduces collisions and increases efficiency.

3. Router:

• Connects different networks and routes data packets between them.
• Operates at the Network Layer; uses IP addresses for packet forwarding.
• Often includes firewall and DHCP capabilities.

Feature	Hub	Switch	Router
Purpose	Connects devices in a network	Connects devices more efficiently	Connects different networks
How Data is Sent	Broadcasts to all devices	Sends data to specific devices	Routes data between networks
Addressing	No addressing	Uses MAC addresses	Uses IP addresses
Efficiency	Low	High	Very High
Cost	Low	Moderate	High
Best Use	Small networks	Medium networks	Larger networks or connecting LANs to WANs (Internet)

3. Uses of Computer Networks

• Resource Sharing: Allows multiple users to share hardware and software resources.
• Communication: Facilitates various forms of communication (email, messaging, video conferencing).
• Remote Access: Enables users to access network resources from remote locations.
• Data Storage: Centralized storage solutions (servers, cloud storage).
• E-commerce: Supports online transactions, banking, and shopping.
• Distributed Computing: Allows collaborative processing and resource utilization across multiple systems.

4. Networks and Types

1. Local Area Network (LAN):

• Limited geographic area (e.g., home, office).
• High speed, low latency.

2. Wireless Local Area Network (WLAN)

   • A wireless version of LAN that uses Wi-Fi technology to connect devices without physical cables.
   • Wireless communication in homes, schools, and businesses.

3. Wide Area Network (WAN):

   • Covers large geographic areas (e.g., city, country).
   • Connects multiple LANs, generally lower speeds.

4. Metropolitan Area Network (MAN):

   • Larger than LAN but smaller than WAN, often spans a city.
   • Connects multiple LANs within a specific geographic area.

5. Personal Area Network (PAN):

• Very small range, typically within a few meters (e.g., connecting mobile devices).
• Common technologies: Bluetooth, Infrared.

6. Virtual Private Network (VPN)

   • A VPN allows users to create a secure network connection over the internet, enabling remote access to a private network.
   • Secure remote access to private networks and data.

5. Introduction to the Internet, browser, web server, URL, domain name, IP address, packets

• Internet: A vast network of interconnected computers that communicate using standardized protocols (TCP/IP).

• Browser: Software used to access and display web content (e.g., Chrome, Firefox).

• Web Server: Stores, processes, and delivers web pages to users.

• URL (Uniform Resource Locator):

  • Address used to access resources on the internet.
  • Structure: scheme (http), host (www.example.com), path (/path/to/resource).

• Domain Name:

  • Human-readable address corresponding to an IP address (e.g., www.example.com).
  • Managed through DNS (Domain Name System).

• IP (Internet Protocol) Address:

• Unique numerical identifier assigned to each device on a network.
• IPv4: 32-bit address (e.g., 192.168.0.1).
• IPv6: 128-bit address to accommodate more devices (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334).

• MAC (Media Access Control)

  • A unique identifier assigned to a device’s network interface card (NIC). Used for communication in local networks (Layer 2 of the OSI model).
  • Format: A 48-bit address, written in hexadecimal, like 00:1A:2B:3C:4D:5E.
    • First half: Identifies the manufacturer (OUI).
    • Second half: Uniquely identifies the device.

• Packets:

• Small units of data transmitted over a network.
• Contains a header (routing information) and a payload (actual data).
• Facilitates efficient data transmission and error handling.

⭐NETWORK MODELS

1. Protocol Layering

Definition

• Protocol Layering: A method of organizing network communication into layers, where each layer serves a specific purpose and interacts with the layers directly above and below it.

Key Concepts

• Encapsulation: Each layer adds its own header (and sometimes a footer) to the data received from the layer above, forming a packet.
• Abstraction: Higher layers do not need to understand the details of the lower layers, promoting modularity.
• Interoperability: Allows different types of networks to communicate with each other using standard protocols.
• Modularity: Each layer performs a specific function in the communication process.

Advantages

• Simplifies Networking: Breaking down the networking process makes it easier to manage and understand.
• Troubleshooting: Easier to diagnose issues within specific layers without affecting the entire system.
• Flexibility: New protocols can be added without affecting existing layers.

2. TCP/IP Protocol Suite (Transmission Control Protocol/Internet Protocol Model)

Overview

• Definition: A set of protocols used for the Internet and similar networks, known for its robust and flexible design.

Layers:

• Application Layer:
• Protocols: HTTP, FTP, SMTP, DNS.
• Functions: User interfaces, data presentation, and application services.

• Transport Layer:
• Protocols: TCP (connection-oriented) and UDP (connectionless).
• Functions: Provides reliable (TCP) or fast (UDP) data transfer; ensures error recovery and flow control.

• Internet Layer:
• Protocol: IP (Internet Protocol).
• Functions: Routing of packets across networks; addressing (IPv4, IPv6).

• Link Layer:
• Protocols: Ethernet, Wi-Fi, PPP.
• Functions: Physical addressing, framing, and managing access to the physical medium.

How the TCP/IP model Works:

• Application Layer: 
• The user interacts with an application (e.g., a web browser) to send or receive data.
• Example: You request a webpage from a web server.

• Transport Layer: 
• The data from the application is broken into segments, and TCP or UDP ensures reliable or fast transmission.
• Example: TCP ensures that the webpage data is sent in order and without errors.

• Internet Layer: 
• The segments are packed into IP packets, and the Internet Layer determines how to route these packets to the destination.
• Example: The IP protocol determines the best route for the packets.

• Link Layer: 
• The packets are formatted into frames and transmitted over the physical network (e.g., Ethernet or Wi-Fi).
• Example: The data is sent over the local network to the next device (router or switch).

• At the receiving end, the reverse process occurs, with each layer processing the data and passing it up to the next layer until the original data is delivered to the application.

Characteristics

• Scalability: Can handle a vast number of devices and networks.
• Interoperability: Supports a wide range of hardware and software configurations.
• Robustness: Handles errors and retransmissions efficiently.

3. OSI Model (Open Systems Interconnection Model)

Overview

• Definition: A conceptual framework that standardizes the functions of a telecommunication or computing system into seven layers.

Layers of the OSI Model

1. Application Layer:

   • Functions: End-user services and application protocols.
   • Examples: HTTP, FTP, SMTP.

2. Presentation Layer:

   • Functions: Data format translation, encryption, and compression.
   • Responsibilities: Ensures that data is in a usable format.

3. Session Layer:

   • Functions: Manages sessions between applications.
   • Responsibilities: Establishes, maintains, and terminates communication sessions.

4. Transport Layer:

   • Functions: Reliable (TCP) or unreliable (UDP) data transfer, segmentation, and flow control.
   • Responsibilities: Ensures complete data transfer and error recovery.

5. Network Layer:

   • Functions: Routing and forwarding of packets.
   • Responsibilities: Logical addressing (IP), packet forwarding, and path determination.

6. Data Link Layer:

   • Functions: Node-to-node data transfer, framing, error detection/correction.
   • Examples: Ethernet, Wi-Fi, PPP.

7. Physical Layer:

• Functions: Transmission of raw bits over a physical medium.
• Responsibilities: Deals with the hardware aspects of networking, such as cables and switches.

How the OSI Model Works

• When data is transmitted over a network, it passes through the OSI model's layers in the following way:

• Application Layer: The application generates data and prepares it for transmission.

• Presentation Layer: The data is formatted and prepared for the network.

• Session Layer: A session is established between the communicating devices.

• Transport Layer: The data is segmented into smaller packets, ensuring reliable transmission.

• Network Layer: The packets are addressed with IP addresses and routed to the destination.

• Data Link Layer: The packets are encapsulated into frames for local transmission.

• Physical Layer: The frames are converted into signals (electrical or optical) and sent over the physical medium.

• At the receiving end, the process is reversed (decapsulation) as each layer extracts the relevant information until the original data is delivered to the application.

Characteristics

• Standardization: Provides a universal set of protocols and guidelines for network communication.
• Interoperability: Facilitates communication between diverse systems and networks.
• Modularity: Each layer can evolve independently, allowing for updates and improvements.

Comparison: TCP/IP vs. OSI Model

• Number of Layers: TCP/IP has 4 layers, while OSI has 7 layers.
• Development: TCP/IP was developed based on practical implementation, while OSI was developed as a theoretical framework.
• Flexibility: TCP/IP is more flexible and widely used in practice, whereas OSI is more comprehensive and ideal for teaching purposes.

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