Revision Notes on Computer Networks (10 Marks) for CBSE Class 12 Computer Science.

Revision Notes on Computer Networks (10 Marks) for CBSE Class 12 Computer Science.

ARPANET (1969): Advanced Research Projects Agency Network. The first network, developed by the US Dept. of Defense.
Internet: The network of networks (worldwide).
Interspace: A client/server software program that allows multiple users to communicate online with real-time audio, video, and text chat in a dynamic 3D environment.

Circuit Switching: A dedicated physical path is established before transmission begins.
- Pros: Guaranteed data rate.
- Cons: Bandwidth wastage if silence occurs.
Packet Switching: Data is broken into small packets. Each packet travels independently via different routes.
- Mechanism: Store and Forward.
- Pros: Efficient line usage; robust.
- Cons: No guarantee of order; latency.

Media	Characteristics	Usage
Twisted Pair	Two copper wires twisted to reduce crosstalk. (CAT5/CAT6).	LANs, Telephone lines.
Coaxial Cable	Copper core, insulation, copper mesh. Faster than twisted pair.	Cable TV.
Fiber Optic	Glass core; transmits data as light. Fastest, expensive, immune to electrical interference.	High-speed backbones, Long distance.

Radio Waves: Omnidirectional (travel in all directions), cheap. Used for FM Radio, WiFi.
Microwaves: Line-of-sight transmission (towers must see each other). Used for TV transmission, Cellular networks.
Infrared: Short-range, cannot pass through walls. Used for TV Remotes.
Satellite: Covers large areas (intercontinental). Expensive.

Modem (Modulator-Demodulator): Converts digital signals to analog (for phone lines) and vice versa.
RJ-45: The standard connector for Ethernet cables (looks like a big phone jack).
Ethernet Card (NIC): Hardware interface that allows a computer to connect to a network. Has a unique MAC Address.
Hub: Broadcasts data to all connected ports (Dumb device). Increases traffic.
Switch: Sends data only to the intended recipient (Smart device). Reduces traffic.
Repeater: Amplifies/Regenerates signals to travel longer distances.
Router: Connects different networks (e.g., LAN to WAN/Internet). Determines the best path.
Gateway: Connects networks with dissimilar protocols (e.g., acting as an exit/entry point for a LAN).

Topologies:

Bus: Single cable (backbone). Cheapest. If backbone breaks, network fails.
Star: All nodes connect to a central Hub/Switch. Easy to troubleshoot. If Hub fails, network fails. (Most common).
Tree: Hierarchical (Star of Stars).
Mesh: Every node connected to every other node. Most expensive, most reliable.

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URL (Uniform Resource Locator): The address of a web resource (e.g., http://www.google.com).
Domain Name: The human-readable name (e.g., google.com).
DNS (Domain Name System): Translates Domain Name into IP Address.
MAC Address: Physical address (Hexadecimal, 48-bit, assigned by manufacturer).
IP Address: Logical address (Dotted decimal, e.g., 192.168.1.1).
Cookie: Small text file stored on user’s browser to track activity/preferences.
Firewall: Hardware or Software to prevent unauthorized access to/from a network.

This is for the question where you have 4 Buildings and need to design a network.

Cable Layout: Always choose the layout with the shortest total cable length. (Usually creates a Star topology around the main block).
Server Placement: Place the Server in the building with the maximum number of computers (to reduce traffic load).
Repeater: Place a Repeater if the cable distance between two blocks is > 70-100 meters.
Hub/Switch: Every building with computers needs a Switch/Hub.
Connecting Hilly/Far areas: Use Radio Waves (if line of sight is okay and cheap) or Satellite (if very far/hilly).

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