🔴 Premium Notes • Unit 2
Networking and Internet
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Topic 1 of 12
1. Computer Network – Basic Concepts
A computer network is a collection of interconnected nodes (devices such as computers, printers, fax machines and telephones) that communicate with each other through a channel to share data and resources.
- Components of a communication system: Sender, Receiver, Message and Channel.
- Sender – the node that sends the data.
- Receiver – the node that receives the data.
- Message – the information or meaningful data being communicated.
- Channel – the communication medium through which the message travels, such as cable or Wi-Fi.
- Advantages of a computer network: Resource Sharing and Communication.
- Resource Sharing – hardware (printers, scanners, memory) and software (applications, files, audio, video) can be shared.
- Communication – information can be exchanged easily and quickly between all nodes of the network.
| Mode | Meaning | Example |
|---|---|---|
| Simplex | Data flows in one direction only (unidirectional). | Radio, Television |
| Half-Duplex | Data flows in both directions, but only one node can transmit at a time. | Walkie-Talkie |
| Full-Duplex | Data flows in both directions at the same time. Used by interactive applications; NIC supports this mode. | Telephone call |
Important Notes
- Important terms: Internet is a global network of networks connected using the TCP/IP protocol.
- Bandwidth is the maximum data transfer rate (capacity) of a network.
- ISP (Internet Service Provider) is a company that provides Internet connectivity, e.g., Jio, Airtel, BSNL.
- Protocol means a set of rules for communication.
Topic 2 of 12
2. Transmission Media
A transmission medium is the channel through which data travels from one node to another in the form of a signal.
| Guided Medium (Wired) | Unguided Medium (Wireless) |
|---|---|
| Uses a physical conductor (cable/wire). | Uses electromagnetic waves; no physical conductor needed. |
| Examples: Twisted Pair cable, Coaxial cable, Optical Fibre. | Examples: Radio waves, Microwaves, Infrared, Satellite links. |
| In twisted pair and coaxial cable the signal travels as voltage/current; in optical fibre it travels as light. | Suitable for mobile devices and long-distance/remote communication. |
Topic 3 of 12
3. Network Devices
| Device | Function |
|---|---|
| Repeater | Restores a weak and distorted signal to its original form so that it can travel a longer distance. Also called a digital generator. |
| Hub | Connects several cable segments through multiple I/O ports. It sends incoming data to all connected lines. |
| Bridge | Connects two or more LANs to form a bigger LAN. It forwards data only towards the destination. |
| Switch | Connects individual nodes; each node is connected to a unique port. It forwards data only to the destination node. |
| Router | Connects different networks (LAN/WAN). It maintains a routing table and decides the best path for each packet. |
| Gateway | Connects networks that use different protocols and converts data from one protocol format to another. |
Difference: Hub vs Switch
| Hub | Switch |
|---|---|
| Sends data to all connected nodes. | Sends data only to the destination node. |
| Not intelligent; causes unnecessary traffic. | Intelligent device; reduces traffic and is faster. |
Topic 4 of 12
4. Types of Networks (Based on Geographical Area)
| Type | Full Form | Coverage / Speed | Example |
|---|---|---|---|
| PAN | Personal Area Network | Around one person, up to 10 metres; wired or wireless. | Bluetooth between phone and PC |
| LAN | Local Area Network | Private network up to 1 km (building/campus); speed 10 Mbps to 1 Gbps. | School computer lab, office network |
| MAN | Metropolitan Area Network | Within a city, radius up to 50 km; connects many LANs. | Cable TV network of a city |
| WAN | Wide Area Network | About 1000 km; connects countries/continents; joins many LANs and MANs. | The Internet |
Topic 5 of 12
5. Network Topology
The arrangement (layout) of nodes in a network is called network topology. It is of two broad kinds: Broadcast (all nodes share one link – Bus, Ring) and Point-to-Point (every pair of nodes has a dedicated link – Star, Mesh).
| Topology | Structure | Advantages | Disadvantages |
|---|---|---|---|
| Bus | All nodes are connected to one long backbone cable through connectors called taps. | Less cabling; easy to install and extend. | Fault detection and isolation is difficult. |
| Ring | All devices are connected in the shape of a ring; data moves in one direction. | Easy to add/remove devices; easy fault detection. | Failure of one node disrupts the whole network; data takes more time to reach. |
| Star | All devices are connected to a central controller called a hub. | Easy to install and configure; easy fault detection. | Needs more cable; if the hub fails, the whole network fails. |
| Mesh | Every node is connected to every other node by a dedicated link. | Very secure data transfer; no traffic problem. | Very large number of cables/connections; difficult and costly to install. |
| Tree | Hybrid of Star + Bus. The backbone cable is the stem; star networks are attached like branches. | Damage to one segment does not affect other segments. | Difficult to install and configure; if the backbone cable fails, the whole network stops. |
Topic 6 of 12
6. Identification of Computers on a Network
- MAC Address: A unique, permanent address assigned to every NIC by its manufacturer.
- It is a 12-digit hexadecimal (48-bit) number written as MM:MM:MM:SS:SS:SS. Example: 00:A0:C9:14:C8:35.
- IP Address: A unique number that identifies every machine on a network.
- It is a group of 4 bytes (32 bits); each byte can be 0 to 255. Example: 59.177.134.72.
- It is assigned by the network administrator or the ISP, so it can change when the computer joins a different network.
Difference: MAC Address vs IP Address
| MAC Address | IP Address |
|---|---|
| Assigned by the manufacturer of the NIC. | Assigned by the network administrator or ISP. |
| Permanent – never changes. | Changes when the computer joins another network. |
| 12-digit hexadecimal (48-bit) number. | 4-byte (32-bit) dotted decimal number. |
| Cannot be used to trace location. | Approximate location can be traced from it. |
Important Notes
- Domain names are easy-to-remember names of web servers, e.g., cbse.nic.in.
- Generic domains: .com, .edu, .gov, .mil, .net, .org. Country domains: .in, .au, .jp, .us.
- Domain Name Resolution is the process of finding the IP address of a domain name using DNS.
Topic 7 of 12
7. Internet Services
| Service | Description |
|---|---|
| Electronic mail that may contain text with attachments. Webmail examples: Gmail, Yahoo. Desktop clients: Outlook, Thunderbird. Protocols: SMTP and POP3. | |
| FTP | Used to upload and download files between a client and a remote server over a TCP network. |
| TELNET | Allows a user to log in to and work on a remote computer after authentication. |
| WWW | A huge collection of linked documents (web pages) stored on machines across the Internet. It works on the HTTP protocol using client–server architecture. |
| Digital Literacy | Knowledge and awareness of using computers, smartphones, software and the Internet effectively. |
Topic 8 of 12
8. Internet Protocol Suite (TCP/IP Model)
Sending data over a network involves many sub-tasks such as addressing, dividing the message, and error control. These tasks are performed by four layers of the TCP/IP model.
| Layer | Function |
|---|---|
| 1. Application Layer | The message is created at the sender's end and processed at the receiver's end; a header is added. Protocols: HTTP, POP3. |
| 2. Transport Layer | Divides the message into segments, adds source and destination port numbers and sequence numbers. Protocols: TCP and UDP. |
| 3. Internet Layer | Adds the source and destination IP addresses. The IP protocol works here and defines the packet format. |
| 4. Link Layer | Adds the physical (MAC) addresses of the sender and receiver to the packet. |
Difference: TCP vs UDP
| TCP | UDP |
|---|---|
| Reliable, connection-oriented protocol. | Unreliable, connectionless protocol. |
| Used when timely, error-free delivery is important (e.g., email, file transfer). | Used for short messages where a fast response matters more than guaranteed delivery (e.g., video streaming). |
Topic 9 of 12
9. Cyber Threats
| Malware | Description |
|---|---|
| Virus | A code that harms the system by overwriting or corrupting files. It copies itself into programs, files or the boot sector. |
| Worm | Comes through the network and automatically creates many copies of itself, flooding the hard disk and congesting the network. |
| Trojan Horse | Appears useful but harms the system. It creates a backdoor through which a hacker can monitor and control the computer. |
Common Cyber Crimes
| Cyber Crime | Meaning |
|---|---|
| Cyber Bullying | Harassing or threatening someone using electronic devices. |
| Cyber Stalking | Repeatedly following/contacting a person online even after clear refusal. |
| Online Job Fraud | Cheating people with false promises of jobs and high salaries. |
| Vishing | Asking for OTP, ATM PIN, CVV, passwords etc. through a phone call. |
| SMSing (Smishing) | Fraud SMS that makes victims call fake numbers or open fake websites. |
| SIM Swap Scam | Fraudulently obtaining a new SIM card of someone's registered number. |
| Credit/Debit Card Fraud | Unauthorised use of another person's card to purchase or withdraw money. |
| Identity Theft | Dishonestly using another person's password, e-signature or unique ID. |
| Spamming | Sending bulk unwanted emails/SMS. |
| Ransomware | Locking the victim's data/device and demanding ransom money to unlock it. |
Important Notes
- Other threats: Eavesdropping, Denial of Service (DoS), and Phishing.
Topic 10 of 12
10. Network Security Tools and Cyber Law
- Firewall: Protects the internal network from malicious traffic coming from external networks. A hardware firewall protects the whole network; a software firewall protects an individual computer.
- Antivirus: Software that detects and removes malicious programs using an updated database of malware definitions.
- Password Manager: Stores all passwords in encrypted form; the user needs only one strong master password.
- SSL (Secure Sockets Layer): A security protocol that secures TCP/IP communication using cryptographic methods.
- Cyber Law: In India, the IT Act 2000 (amended as the IT Amendment Act 2008) defines cyber offences and their penalties.
Important Notes
- Protective Measures: Never click on suspicious links. Use strong passwords. Keep browser, antivirus and firewall updated.
- Do not accept friend requests from unknown people; never post offensive content or spread rumours.
- If someone harasses you online, take a screenshot, block the person and report to the site administrator.
- Check the spelling of website addresses carefully to avoid phishing websites.
- Delete cookies and temporary files periodically.
Topic 11 of 12
11. Important Full Forms (Frequently Asked)
| Term | Full Form |
|---|---|
| NIC | Network Interface Card |
| MAC | Media Access Control |
| IP | Internet Protocol |
| TCP | Transmission Control Protocol |
| UDP | User Datagram Protocol |
| HTTP | HyperText Transfer Protocol |
| FTP | File Transfer Protocol |
| SMTP | Simple Mail Transfer Protocol |
| POP3 | Post Office Protocol version 3 |
| TELNET | TErminaL NETwork |
| WWW | World Wide Web |
| URL | Uniform Resource Locator |
| DNS | Domain Name Server / System |
| ISP | Internet Service Provider |
| LAN / MAN / WAN / PAN | Local / Metropolitan / Wide / Personal Area Network |
| DoS | Denial of Service |
| SSL | Secure Sockets Layer |
Topic 12 of 12
12. Word Meanings (Simple English)
| Word | Simple Meaning |
|---|---|
| Node / Station | Any device connected to a network (computer, printer, phone). |
| Channel / Medium | The path through which data travels. |
| Protocol | A set of rules for communication. |
| Bandwidth | The maximum data-carrying capacity (speed) of a network. |
| Packet | A small piece of a message sent over a network. |
| Server | A powerful computer that provides services to other computers. |
| Client | A computer that requests and uses services from a server. |
| Hyperlink | A link that takes you from one web page to another. |
| Malicious | Harmful; intended to cause damage. |
| Unauthorised | Without permission. |
| Intrusion | Entering a system without permission. |
| Encrypt / Decrypt | To convert data into secret code / to convert it back to normal. |
| Authenticate | To verify identity (e.g., with a username and password). |
| Backdoor | A hidden entry into a system used by hackers. |
| Ransom | Money demanded to release locked data or a device. |
Important Notes
- All the Best for Your Examination!
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