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Internet and Networking Overview

Oct 4, 2025

Overview

This lecture provides a detailed, step-by-step explanation of how the internet and computer networks function. It covers foundational concepts, historical context, technical infrastructure, protocols, network types, topologies, the OSI model, and real-world examples. The content is especially useful for students and anyone preparing for exams or interviews in networking.

Introduction to the Internet

  • The internet is a global system of interconnected computer networks and electronic devices that communicate using established protocols (rules).
  • It enables the transfer of information from one device to another by following these protocols.
  • Data is transmitted in the form of packets. Each packet contains a header with the source and destination IP addresses, as well as other metadata (such as sequence number and time-to-live).
  • Protocols like TCP/IP ensure that data is delivered reliably, in order, and without loss.
  • The internet is essentially a network of networks, connecting devices worldwide.

History and Evolution of the Internet

  • The internet originated after World War II, during the Cold War, as a response to the need for secure, decentralized communication in the USA.
  • The U.S. government created ARPA (Advanced Research Projects Agency), later known as DARPA, to develop a resilient network (ARPANET) that could survive attacks and prevent data loss.
  • ARPANET initially connected four universities: UCLA, Stanford, UC Santa Barbara, and the University of Utah. Data was sent in packets to avoid single points of failure.
  • Paul Baran proposed packet switching, allowing data to be broken into small packets and reassembled at the destination.
  • In 1969, the first message was sent over ARPANET, marking the birth of the internet.
  • In 1983, Vint Cerf and Bob Kahn introduced the TCP/IP protocol suite, standardizing communication rules and enabling interoperability between different networks.
  • The National Science Foundation (NSF) developed NSFNET, expanding the network’s reach.
  • In the 1990s, Tim Berners-Lee invented the World Wide Web (WWW), HTML (HyperText Markup Language), and HTTP (HyperText Transfer Protocol), making the internet accessible to the public via browsers.
  • The Domain Name System (DNS) was introduced to map human-readable domain names to IP addresses, simplifying navigation.
  • The internet has continued to evolve, with the introduction of IPv6, cloud computing, streaming, AI, and SaaS.

Data Transmission and Infrastructure

  • Data transmission involves multiple steps and devices:
    • Data is created by an application (e.g., WhatsApp) and encrypted for security (end-to-end encryption).
    • The message is split into packets, each with headers containing source/destination IPs, port numbers, and metadata.
    • Data is sent from the device to a router, which assigns a local (private) IP address and port number.
    • The router uses Network Address Translation (NAT) to convert private IPs to public IPs for internet communication.
    • Data is sent to the Internet Service Provider (ISP), which determines the shortest path to the destination.
    • Data travels across the globe via undersea optical fiber cables, which connect continents and are managed by major companies.
    • At the destination, data is reassembled, decrypted, and delivered to the recipient’s application.
    • If the recipient is offline, the server stores the encrypted message until the recipient comes online.
  • The Domain Name System (DNS) translates domain names (e.g., google.com) into IP addresses, allowing users to access websites without memorizing numeric addresses.
  • Data transfer is monitored using tools like ping and network panels, which show packet size, sequence, status codes, and transfer times.

IP Addresses and Ports

  • IP Address: A unique identifier for each device on a network.
    • IPv4: 32-bit address (e.g., 192.168.0.1), supports ~4.3 billion addresses. Format: four numbers (0-255) separated by dots.
    • IPv6: 128-bit address, supports a vastly larger number of devices. Format: eight groups of four hexadecimal digits (0-9, A-F), separated by colons.
    • IPv6 was introduced due to the exhaustion of IPv4 addresses.
  • Port Number: Identifies specific applications or services on a device.
    • Range: 0–65535.
    • Well-known ports (0–1023) are reserved for system services (e.g., HTTP uses 80, HTTPS uses 443).
    • Application ports (1024–49151) are used by user applications.
    • Temporary/dynamic ports (49152–65535) are used for short-lived connections.
  • NAT (Network Address Translation): Converts private IP addresses (used within local networks) to public IP addresses (used on the internet), enabling multiple devices to share a single public IP.
  • MAC Address: A unique hardware identifier for network interfaces, used within local networks for device identification.

Types of Networks

  • PAN (Personal Area Network): Short-range network (up to 10 meters), typically connects personal devices via Bluetooth or USB (e.g., phone to earbuds).
    • Low cost, fast connection, limited range, moderate security.
  • LAN (Local Area Network): Connects devices within a limited area (home, office, school).
    • High speed, good security (firewalls), limited to a building or small campus.
  • MAN (Metropolitan Area Network): Covers a city or large campus, connecting multiple LANs.
    • Used by cable TV networks, city-wide Wi-Fi, or large organizations.
    • Higher cost and range than LAN, but less than WAN.
  • WAN (Wide Area Network): Spans countries or continents, connecting multiple LANs and MANs.
    • The internet is the largest WAN.
    • Lower speed, higher risk of hacking, complex management.
  • CAN (Campus Area Network): Connects multiple buildings within a campus (e.g., university, business park).
    • Larger than LAN, smaller than MAN, used for campus-wide connectivity.

Network Topologies

  • Bus Topology: All devices are connected to a single backbone cable.
    • Cost-effective, easy to add devices, but if the backbone fails, the network goes down.
  • Ring Topology: Devices are connected in a circular fashion; data passes through each node.
    • Fast data transfer, easy to identify faults, but if one device fails, the network can be disrupted.
  • Star Topology: All devices connect to a central hub or switch.
    • Easy to add/remove devices, high performance, but if the central hub fails, the network is affected.
  • Mesh Topology: Every device is connected to every other device.
    • High reliability, no single point of failure, but expensive and complex to set up.
  • Tree Topology: Hierarchical structure combining star and bus topologies.
    • Used in large organizations, easy to manage groups, but dependent on backbone and central devices.
  • Hybrid Topology: Combination of two or more topologies to meet specific needs.
    • Flexible, scalable, but can be complex to design and manage.
  • Other Topologies:
    • Point-to-Point: Direct connection between two devices.
    • Daisy Chain: Devices connected in series, forming a chain.

OSI Model (Open Systems Interconnection)

  • The OSI model is a conceptual framework that standardizes network communication in seven layers, each with specific functions:
    1. Physical Layer: Transmits raw bits over physical media (cables, radio waves). Handles encoding, signaling, and transmission.
    2. Data Link Layer: Ensures reliable data transfer between devices on the same network. Handles MAC addressing, error detection, and framing.
    3. Network Layer: Routes data between networks using IP addresses. Handles packet forwarding and addressing.
    4. Transport Layer: Manages end-to-end communication, segmentation, sequencing, and error recovery. Uses protocols like TCP and UDP.
    5. Session Layer: Establishes, manages, and terminates sessions between applications. Handles checkpoints and recovery.
    6. Presentation Layer: Translates, encrypts, and compresses data. Ensures data is in a usable format for the application layer.
    7. Application Layer: Closest to the user; provides network services to applications (e.g., HTTP, SMTP, FTP).
  • Data flows from the application layer down to the physical layer on the sender’s side, and from the physical layer up to the application layer on the receiver’s side.
  • The OSI model helps troubleshoot network issues and ensures interoperability between different systems.

Client-Server and Peer-to-Peer Architectures

  • Client-Server Architecture:
    • Clients (e.g., browsers, apps) send requests to centralized servers, which process and respond (e.g., web browsing, email).
    • Servers are specialized computers or programs designed to handle requests and provide resources or services.
    • Example: Accessing Instagram—your device (client) requests data from Instagram’s servers.
  • Peer-to-Peer (P2P) Architecture:
    • Devices (peers) communicate directly, acting as both clients and servers.
    • No central server; each device can request and provide resources.
    • Used in file sharing (e.g., torrents), blockchain, and decentralized applications.
    • Advantages: No single point of failure, cost-effective, scalable.
    • Disadvantages: Security concerns, data consistency challenges.

Protocols

  • Protocols are sets of rules that govern data communication over networks. They define how data is formatted, transmitted, received, and acknowledged.
  • Key Protocols:
    • HTTP (HyperText Transfer Protocol): Application layer protocol for web communication. Uses port 80.
    • HTTPS (HTTP Secure): HTTP with encryption (SSL/TLS) for secure communication. Uses port 443.
    • TCP (Transmission Control Protocol): Transport layer protocol ensuring reliable, ordered, and error-checked delivery of data. Connection-oriented, uses three-way handshake, sequencing, and acknowledgments.
    • UDP (User Datagram Protocol): Transport layer protocol for fast, connectionless, and unreliable data transfer. No sequencing or acknowledgment; used in live streaming, gaming, and voice/video calls.
    • IP (Internet Protocol): Network layer protocol for addressing and routing packets. Adds source and destination IP addresses to each packet.
    • DNS (Domain Name System): Application layer protocol that translates domain names to IP addresses.
    • FTP (File Transfer Protocol): Application layer protocol for file transfer.
    • SMTP (Simple Mail Transfer Protocol): Application layer protocol for sending emails.
    • NAT (Network Address Translation): Not a protocol, but a process for translating private IPs to public IPs.
    • SSL/TLS (Secure Sockets Layer/Transport Layer Security): Protocols for encrypting data, used in HTTPS.
  • Port Numbers:
    • HTTP: 80
    • HTTPS: 443
    • FTP: 21
    • SMTP: 25
    • DNS: 53
    • Custom applications may use other ports (e.g., 3000, 5500, etc.).
  • Protocol Functions:
    • Define data formats and communication rules.
    • Ensure data is delivered, acknowledged, and retransmitted if lost (TCP).
    • Provide security through encryption (HTTPS, SSL/TLS).
    • Enable routing and addressing (IP).
    • Allow translation of human-readable names to machine addresses (DNS).

Key Terms & Definitions

  • Internet: A worldwide system of interconnected computer networks using protocols to communicate and transfer data.
  • Protocol: A set of rules that governs data communication between devices.
  • Packet: A small unit of data transmitted over a network, containing headers (with source/destination info) and payload (actual data).
  • IP Address: A unique identifier for a device on a network (IPv4 or IPv6).
  • Port Number: A numerical identifier for specific applications or services on a device.
  • MAC Address: A unique hardware identifier for network interfaces, used within local networks.
  • DNS (Domain Name System): Translates domain names (e.g., www.example.com) to IP addresses.
  • OSI Model: A seven-layer conceptual framework for standardizing network communication.
  • TCP (Transmission Control Protocol): Ensures reliable, ordered delivery of data packets.
  • UDP (User Datagram Protocol): Enables fast, connectionless data transfer without guarantees.
  • NAT (Network Address Translation): Converts private IP addresses to public IP addresses for internet communication.
  • VPN (Virtual Private Network): Creates an encrypted connection over the internet, masking the user’s IP address and enhancing privacy.

Action Items / Next Steps

  • Review and revise your notes for each section to reinforce understanding.
  • Research Daisy Chain Topology and Point-to-Point Topology for additional network structures.
  • Use GPT or other resources to explain how Zomato order data flows through the OSI model, step by step.
  • Explore practical examples of VPNs, firewalls, and protocol use in real-world applications.
  • Practice using network tools (e.g., ping, traceroute, network panels) to observe packet flow and protocol behavior.
  • Consider drawing diagrams of network topologies and the OSI model to visualize concepts.

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