Database Concepts

COMPUTER NETWORKS: COMPLETE STUDY NOTES

1. Introduction to Computer Networks: A computer network is defined as an interconnection among two or more computers or computing devices. This interconnection allows these devices to share data and resources with one another. In our daily lives, we encounter various types of networks, such as social networks, mobile networks, and the interconnected systems used by airlines, banks, and hospitals.

The size of a network can vary significantly, from a few devices in a single room to millions of devices spread across the globe. A computer network can include various types of hosts (also called nodes), such as servers, desktops, laptops, smartphones, and even smart home appliances like TVs and refrigerators.

Data Communication within these networks refers to the exchange of data between these connected devices. This exchange involves five major components:

1. Sender: The device that initiates and sends the data.

2. Receiver: The device intended to receive the data.

3. Message: The actual information (text, image, audio, video) being exchanged.

4. Communication Media: The path (wired or wireless) through which the message travels.

5. Protocols: A standard set of rules followed by the communicating parties to ensure successful data exchange.

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2. Evolution of Networking: The journey of modern computer networks began in the 1960s with a research project commissioned by the ARPANET (Advanced Research Projects Agency Network) in the U.S. Department of Defence. The primary goal was to connect academic and research institutions for scientific collaboration.

Key Milestones in Networking Evolution:

• 1969: ARPANET became functional, connecting UCLA and Stanford Research Institute (SRI).

• 1971: Roy Tomlinson developed network messaging or E-mail, introducing the '@' symbol.

• 1974: The first commercial use of ARPANET was established under the name Telenet.

• 1982: The term Internet was coined.

• 1983: TCP/IP was introduced as the standard protocol for ARPANET.

• 1984: The Domain Name System (DNS) was introduced.

• 1986: The National Science Foundation launched NSFNET, bringing connectivity to more people.

• 1990: Tim Berners-Lee at CERN developed HTML and URL, giving birth to the World Wide Web (WWW).

• 1997: The first version of the Wi-Fi (802.11) standard was introduced.

3. Network Types: Computer networks are broadly categorised based on the geographical area they cover and their data transfer rates.

A. Personal Area Network (PAN): A PAN is formed by connecting personal devices like computers, laptops, smartphones, and printers within a very short range, approximately 10 metres.

• Wired PAN: A phone connected to a laptop via USB.

• Wireless PAN (WPAN): Devices communicating through Bluetooth technology.

B. Local Area Network (LAN): A LAN connects nodes placed at a limited distance, such as a single room, an office building, a school, or a college campus.

• Connectivity: Uses wires, Ethernet cables, fibre optics, or Wi-Fi.

• Speed: High data transfer rates, typically varying from 10 Mbps (Ethernet) to 1000 Mbps (Gigabit Ethernet).

• Security: Comparatively secure, as only authorised users can access shared resources.

C. Metropolitan Area Network (MAN): A MAN is an extended form of LAN that covers a larger geographical area, such as an entire city or town.

• •Range: Can extend up to 30–40 km.

• Examples: Cable TV networks and cable-based broadband internet services.

• Structure: Often formed by connecting many LANs together.

D. Wide Area Network (WAN): A WAN connects computers, LANs, and MANs spread across different geographical locations, countries, or even continents.

• Connectivity: Established via wired or wireless media, including satellite links.

• The Internet: The largest existing WAN, connecting billions of devices globally.

4. Network Devices: To facilitate communication and manage data flow, various hardware devices are required.

• Modem (MOdulator DEModulator): Converts digital bits from a computer into analog signals for transmission over telephone lines, and vice versa at the receiving end.

• Ethernet Card (NIC): A circuit board installed in a computer that acts as an interface between the computer and the network. Each NIC has a unique, permanent MAC address.

• RJ45 (Registered Jack-45): An eight-pin connector used at the end of Ethernet cables to plug into NICs.

• Repeater: An analog device used to regenerate signals. Since signals lose strength after travelling a certain distance (usually 100m), a repeater puts the original signal strength back onto the cable.

• Hub: A device used to connect multiple devices through wires. It is a "broadcast" device; data arriving on one port is sent out to all other ports, which can lead to data collisions if two devices send data at once.

• Switch: A more "intelligent" version of a hub. It extracts the destination address from a data packet and sends it only to the intended device. It does not forward noisy or corrupted signals.

• Router: A device that receives, analyses, and transmits data packets between different networks. It can repackage data to fit different network types and provides Wi-Fi access in homes.

• Gateway: A key access point that acts as a "gate" between a private network and the outside Internet. It serves as the entry and exit point for all incoming and outgoing data.

5. Network Topologies: The arrangement or physical layout of computers and peripherals in a network is called its topology.

A. Mesh Topology

Every device is connected to every other device in the network.

• Pros: Highly reliable (if one node fails, others continue); secure; handles large traffic.

• Cons: Complex wiring; high cabling cost; many unutilised connections.

• Formula: To connect n nodes, it requires n(n−1)/2 wires.

B. Ring Topology: Each node is connected to exactly two other devices, forming a circular path.

• Mechanism: Data transmission is unidirectional (clockwise or counterclockwise).

• Reliability: Considered less reliable than mesh.

C. Bus Topology: All nodes are connected to a single central backbone wire called a "bus".

• Pros: Cheaper and easier to maintain.

• Cons: Less secure and less reliable; if the backbone cable fails, the whole network goes down.

D. Star Topology: Each device is connected to a central networking device like a hub or a switch.

• Pros: Very effective and fast; failure of one node doesn't affect others.

• Cons: Central point of failure; if the central hub/switch fails, the entire network fails.

E. Tree (Hybrid) Topology: A hierarchical topology with multiple branches. Each branch can contain different basic topologies like star, ring, or bus.

Usage: Usually implemented in WANs to connect multiple LANs.

6. Identifying Nodes: MAC vs. IP Address: Every node in a network must be uniquely identified so that data packets can be routed correctly.

MAC Address (Media Access Control)

• Nature: Physical or hardware address.

• Permanence: Engraved on the NIC at the time of manufacturing; it can never be changed.

• Format: A 12-digit hexadecimal number (48 bits). The first 6 digits identify the manufacturer (OUI), and the last 6 are the serial number.

IP Address (Internet Protocol)

• Nature: Logical address used to identify a node on a network using Internet Protocol.

• Permanence: Can change if a node moves to a different network.

Versions:

• IPv4: A 32-bit address written as four decimal numbers (0–255) separated by periods (e.g., 192.168.0.1).

• IPv6: A 128-bit address designed to provide more unique addresses. It consists of eight groups of hexadecimal numbers separated by colons.

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7. Difference Between Internet and Web: While often used interchangeably, the Internet and the Web are technically different concepts.

The Internet: The global hardware infrastructure of interconnected computers, cables, routers, and servers. It is the "network of networks" that allows devices to communicate.

The World Wide Web (WWW): An information system built on top of the Internet. It consists of trillions of interlinked web pages and resources (designed using HTML) that are accessed via URLs (Uniform Resource Locators) using the HTTP protocol.

Domain Name System (DNS): Since it is hard for humans to remember numerical IP addresses, servers are given names called Domain Names (e.g., ncert.nic.in). A DNS Server maintains a database of these names and their corresponding IP addresses, performing "domain name resolution" whenever you type a web address into your browser.

8. Summary Table: Comparison of Addresses