Chapter 10: Computer Networks

CBSE Unit: Unit 2, Computer Networks (10 marks shared with Ch 11, 12) Marks Weightage: ~4-5 marks Priority: HIGH, theory-heavy, direct definitions and short-answer questions

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Key Concepts

10.1 Introduction to Computer Networks, A computer network is an interconnection among two or more computers or computing devices, Allows computers to share data and resources

• Networking devices (switch, router, modem) connect multiple computers, Data is divided into smaller chunks called packets for transmission, Devices connect via wired media (cables) or wireless media (air), A node is any device in a network that can receive, create, store, or send data (modem, hub, bridge, switch, router, printer, computer, server)

10.2 Evolution of Networking

Year	Milestone
1961	ARPANET concept developed
1969	ARPANET became functional (UCLA and SRI connected)
1971	Roy Tomlinson develops email; @ symbol introduced
1974	Term "Internet" coined; Telenet (first commercial use of ARPANET)
1982	TCP/IP introduced as standard protocol on ARPANET
1983	Domain Name System (DNS) introduced
1986	NSFNET program by National Science Foundation
1990	Tim Berners-Lee develops HTML and URL at CERN (birth of WWW)
1997	First version of Wi-Fi (802.11) standard

10.3 Types of Networks

Type	Full Form	Range	Speed	Example
PAN	Personal Area Network	~10 metres	Varies	Bluetooth devices, USB-connected phone
LAN	Local Area Network	Up to 1 km	10 Mbps to 1000 Mbps	School, office, campus
MAN	Metropolitan Area Network	30-40 km	Mbps (less than LAN)	Cable TV network, city broadband
WAN	Wide Area Network	Countries/Continents	Lower than LAN/MAN	The Internet

PAN (Personal Area Network), Connects personal devices within ~10 metres, Wired PAN: phone connected to laptop via USB, Wireless PAN (WPAN): smartphones communicating via Bluetooth

LAN (Local Area Network), Covers room, floor, office, campus, Connected via wires, Ethernet cables, fibre optics, or Wi-Fi, Comparatively secure (only authenticated users), Data transfer: 10 Mbps (Ethernet) to 1000 Mbps (Gigabit Ethernet)

• Ethernet: set of rules for connecting devices through cables in a LAN

MAN (Metropolitan Area Network), Extended LAN covering a city or town, Cable TV or cable broadband are examples, Can extend up to 30-40 km, Often formed by connecting multiple LANs

WAN (Wide Area Network), Connects LANs and MANs across countries/continents

• The Internet is the largest WAN
• Used by large organizations for inter-branch connectivity

10.4 Network Devices

Device	Function
Modem	MOdulator-DEModulator; converts digital signals to analog and vice versa
Ethernet Card / NIC	Network Interface Card; connects computer to wired network; has unique MAC address
RJ45	8-pin connector used with Ethernet cables
Repeater	Analog device that regenerates weakened signals (typically after ~100m)
Hub	Sends incoming data to ALL connected devices; collisions possible
Switch	Sends data only to the destination device (reads destination address); drops corrupted signals
Router	Receives, analyses, and transmits data to other networks; can repackage data; connects LAN to Internet
Gateway	Entry/exit point of a network; routes data between different networks; often integrated with firewall

Key differences:

• Hub sends to ALL ports; Switch sends only to destination, Switch works within a LAN; Router connects different networks, Gateway connects networks with potentially different protocols

10.5 Networking Topologies

The arrangement of computers and peripherals in a network is called its topology.

Mesh Topology, Every device connected to every other device

• Wires needed: n(n-1)/2 for n nodes, Advantages: handles large traffic, reliable (no single point of failure), secure, Disadvantages: complex wiring, high cost, redundant connections

Ring Topology, Each node connected to two other devices (left and right), Data flow is unidirectional (clockwise or counterclockwise), Less secure and less reliable

Bus Topology, All devices connected to a single backbone wire (bus)

• Data sent in both directions on the bus, Can be received by any connected node
• Cheaper and easier to maintain, Less secure and less reliable

Star Topology, Every device connected to a central node (hub/switch), Effective, efficient, and fast, Failure of one device does not affect others, But failure of central device = entire network fails

• Central device can be broadcasting (to all) or unicast (to specific node)

Tree / Hybrid Topology

• Hierarchical structure with multiple branches, Each branch can have star, ring, or bus topology, Usually realized in WANs connecting multiple LANs, Example: 4 star topologies connected via a bus

10.6 Identifying Nodes in a Network

MAC Address (Media Access Control)

• Physical/hardware address permanently engraved on NIC during manufacturing
• Cannot be changed
• 48 bits = 12 hexadecimal digits
• First 6 digits (24 bits) = Manufacturer ID (OUI, Organisational Unique Identifier), Last 6 digits (24 bits) = Serial number assigned by manufacturer

IP Address (Internet Protocol), Logical address used to uniquely identify nodes on a network

• Can change when node moves to different network (unlike MAC)

IPv4:

• 32-bit address, Written as 4 numbers separated by periods (each 0-255), Example: 192.168.0.178, Offers ~4.3 billion unique addresses

IPv6:

• 128-bit address, Written as 8 groups of hexadecimal numbers separated by colons, Example: 2001:CDBA:0000:0000:0000:0000:3257:9652

Feature	MAC Address	IP Address
Type	Physical/Hardware	Logical
Permanence	Permanent (cannot change)	Can change with network
Length	48 bits (12 hex digits)	IPv4: 32 bits, IPv6: 128 bits
Assigned by	Manufacturer	Network administrator/DHCP

10.7 Internet, Web, and IoT

• Internet: Global network of computing devices (largest WAN), Architecture: Device --> Modem --> Local ISP --> National Network --> Internet Backbone
• Internet is NOT the same as the Web (WWW)

World Wide Web (WWW), Invented by Sir Tim Berners-Lee at CERN in 1990

• Ocean of information stored as interlinked web pages and resources, Accessed through the Internet, Three fundamental technologies:

Technology	Full Form	Purpose
HTML	HyperText Markup Language	Design standardised web pages
URL/URI	Uniform Resource Locator / Identifier	Unique address for each web resource
HTTP	HyperText Transfer Protocol	Rules for retrieving linked web pages
HTTPS	HTTP Secure	More secure version of HTTP

Internet vs WWW:

• Internet = huge global network of interconnected computers, WWW = collection of interlinked web pages on computers accessible over the Internet, Internet is the infrastructure; Web is a service that runs on it

10.8 Domain Name System (DNS), Each server hosting a website has an IP address

• Domain name = human-readable name assigned to a server's IP address, Examples: ncert.nic.in = 164.100.60.233, wikipedia.org = 198.35.26.96

DNS Server, Converts domain name to corresponding IP address (domain name resolution), DNS servers are placed in hierarchical order

• 13 root servers at the top (named A through M; 10 in US, 1 London, 1 Stockholm, 1 Japan), Maintained by IANA (Internet Assigned Numbers Authority), Process: Browser --> DNS Server (gets IP) --> HTTP retrieves page from that IP

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Important Definitions

1. Computer Network: Interconnection among two or more computers for sharing data/resources
2. Node: Any device in a network that can receive, create, store, or send data
3. Packet: Smaller chunks of data transmitted over a network
4. LAN: Network covering limited area (room, campus) with high speed
5. MAN: Extended LAN covering a city or town
6. WAN: Network spanning countries or continents
7. Ethernet: Set of rules for connecting devices through cables in a LAN
8. Topology: Arrangement of computers and peripherals in a network
9. Modem: Device converting between analog and digital signals
10. NIC: Network Interface Card connecting computer to network
11. MAC Address: Permanent 48-bit hardware address on NIC
12. IP Address: Logical address identifying each node on a network
13. DNS: System that converts domain names to IP addresses
14. URL: Unique address/path for each web resource
15. WWW: Collection of interlinked web pages accessible over the Internet
16. ISP: Internet Service Provider; organization providing Internet access
17. Gateway: Entry/exit point of a network

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Common Board Exam Question Patterns

1. Expand abbreviations (1 mark): ARPANET, MAC, ISP, URI, LAN, WAN, MAN, PAN, DNS, HTML, HTTP, NIC, TCP/IP
2. Differentiate between (2 marks): LAN vs WAN, Hub vs Switch, Internet vs WWW, MAC vs IP address, Star vs Bus topology
3. Explain network devices (2-3 marks): Switch, Repeater, Router, Gateway, NIC, Modem
4. Identify topology from description (1-2 marks): "Each node connected via single cable" = Bus
5. Draw topology connecting N computers (2 marks): Star or Bus topology diagram
6. Types of networks (2 marks): Given a scenario, identify PAN/LAN/MAN/WAN
7. DNS explanation (2 marks): What is DNS? How does it work?
8. MAC address (1-2 marks): Significance, format (48 bits, 12 hex digits)
9. IPv4 vs IPv6 (1-2 marks): Bit length, format, why IPv6 was needed

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Key Points Students Miss

1. Internet is NOT the same as WWW, Internet is the network; WWW is web pages on it
2. MAC address is permanent; IP address can change when switching networks
3. Hub broadcasts to ALL; Switch sends only to destination, critical difference
4. Mesh topology formula: n(n-1)/2 connections for n nodes
5. Star topology: central device failure = entire network failure (single point of failure)
6. Ring topology is unidirectional; data flows in one direction only
7. IPv4 = 32 bits (4 numbers, each 0-255); IPv6 = 128 bits (8 hex groups)
8. Modem is needed for analog-to-digital conversion (and vice versa)
9. Repeater regenerates signals (does not amplify, it regenerates)
10. Router connects different networks; Switch connects devices within same network
11. DNS does domain name resolution (name to IP), not the other way around
12. Tim Berners-Lee invented WWW in 1990 at CERN (frequently asked)