Network types
| Type | Full form | Coverage / example |
|---|---|---|
| PAN | Personal Area Network | A few metres – Bluetooth earbuds, phone to laptop |
| LAN | Local Area Network | Office, branch or building; Ethernet, Wi-Fi |
| MAN | Metropolitan Area Network | A city; cable TV network |
| WAN | Wide Area Network | Countries / world; the Internet is the largest WAN |
Intranet = private network for employees only; Extranet = intranet partly opened to partners, suppliers or customers; VPN = encrypted tunnel over a public network.
Topologies
| Topology | Layout | Point to remember |
|---|---|---|
| Bus | All nodes on one backbone cable | Backbone failure stops the network; terminators at ends |
| Star | All nodes to a central hub/switch | Most common in LANs; hub failure stops the network |
| Ring | Each node connected to two neighbours in a loop | Data travels in one direction; token passing |
| Mesh | Every node connected to every other | Links = n(n−1)/2; most reliable, most expensive |
| Tree | Hierarchy of star networks | Root node at the top |
| Hybrid | Mix of two or more | Large organisations |
OSI model (7 layers)
| No. | Layer | Function | Data unit / devices / protocols |
|---|---|---|---|
| 7 | Application | Network services to the user | HTTP, FTP, SMTP, DNS, Telnet |
| 6 | Presentation | Translation, encryption, compression | JPEG, ASCII, SSL/TLS (textbook) |
| 5 | Session | Establishes, manages, ends sessions | NetBIOS, RPC |
| 4 | Transport | End-to-end delivery, segmentation, error and flow control | Segment; TCP, UDP |
| 3 | Network | Logical (IP) addressing and routing | Packet; router; IP, ICMP |
| 2 | Data Link | Framing, MAC addressing, error detection | Frame; switch, bridge |
| 1 | Physical | Transmits raw bits over the medium | Bits; hub, repeater, cables |
Mnemonic (7 to 1): All People Seem To Need Data Processing. The OSI model was published by ISO.
TCP/IP model (4 layers)
Application (OSI 5–7) → Transport (OSI 4) → Internet (OSI 3, IP addressing and routing) → Network Access / Link (OSI 1–2). TCP/IP was developed by Vint Cerf and Bob Kahn.
TCP is connection-oriented and reliable (acknowledgements, retransmission). UDP is connectionless, faster, with no delivery guarantee (video streaming, online games, DNS queries).
Protocols and port numbers
| Protocol | Full form / use | Port |
|---|---|---|
| FTP | File Transfer Protocol | 20 (data), 21 (control) |
| SSH | Secure Shell – encrypted remote login | 22 |
| Telnet | Unencrypted remote login | 23 |
| SMTP | Simple Mail Transfer Protocol – sending mail | 25 (587 for client submission) |
| DNS | Domain Name System – names to IP addresses | 53 |
| DHCP | Dynamic Host Configuration Protocol – assigns IP automatically | 67 (server), 68 (client) |
| HTTP | HyperText Transfer Protocol | 80 |
| POP3 | Post Office Protocol v3 – download mail | 110 |
| IMAP | Internet Message Access Protocol – mail synced on server | 143 |
| SNMP | Simple Network Management Protocol | 161 |
| HTTPS | HTTP secured with TLS | 443 |
| RDP | Remote Desktop Protocol | 3389 |
ARP finds the MAC address for a known IP address; ICMP carries error messages and is used by ping.
IPv4 vs IPv6
| Feature | IPv4 | IPv6 |
|---|---|---|
| Length | 32 bits | 128 bits |
| Format | 4 decimal numbers (0–255) separated by dots, e.g. 192.168.1.10 | 8 groups of 4 hex digits separated by colons, e.g. 2001:0db8::1 |
| Address space | About 4.3 billion (2^32) | 2^128 |
| Broadcast | Yes | No (uses multicast and anycast) |
| Security | IPsec optional | IPsec support built in |
Loopback: 127.0.0.1 (IPv4), ::1 (IPv6). Private IPv4 ranges: 10.x.x.x, 172.16–31.x.x, 192.168.x.x. A MAC address is 48 bits, written as six pairs of hex digits.
Network devices
- Hub – broadcasts to all ports (Layer 1).
- Repeater – regenerates weak signals (Layer 1).
- Switch – sends frames only to the destination port using MAC addresses (Layer 2).
- Bridge – joins two LAN segments (Layer 2).
- Router – connects different networks using IP addresses (Layer 3).
- Gateway – connects networks with different protocols (protocol converter).
- Modem – modulator-demodulator; converts digital to analog and back.
- NIC – network interface card; holds the MAC address.
Transmission modes and media
Simplex (one way only – TV broadcast, keyboard to CPU), half-duplex (both ways, one at a time – walkie-talkie), full-duplex (both ways together – telephone). Media: twisted pair (RJ-45), coaxial, optical fibre (light pulses, highest bandwidth), radio, microwave, satellite. Bandwidth is measured in bits per second (bps, Mbps, Gbps). Wi-Fi = IEEE 802.11; Ethernet = IEEE 802.3; Bluetooth = originally IEEE 802.15.1.
Internet basics
- ARPANET (1969, US Department of Defense) – forerunner of the Internet.
- WWW – invented by Tim Berners-Lee at CERN in 1989; uses HTML, HTTP and URLs.
- URL – Uniform Resource Locator:
https://www.example.co.in/page= protocol + domain + path..inis India's country-code top-level domain;.com,.org,.govare generic/sponsored TLDs. - ISP – Internet Service Provider. Browser – Chrome, Edge, Firefox. Search engine – Google, Bing.
- Cookies – small text files saved by websites in the browser.
- E-mail – CC (copy, visible to all), BCC (blind copy, hidden from other recipients). Ray Tomlinson sent the first network e-mail using @.
- VoIP – voice calls over the Internet.