Internet, IoT, Search Engines & Messaging
Ultimate CS Exam Guide — RPSC (BCI/SCI), DSSSB, NIELIT, KVS/NVS, UGC NET, REET, IA & State/Central Exams
Internet Core
TCP/IP, Protocols, Ports
IoT
MQTT, CoAP, Zigbee, LoRaWAN
Search Engines
Crawling, Indexing, Ranking
Messaging
Online vs Offline
Contents
1. The Internet & Networking Core
The Internet is a globally distributed system of interconnected computer networks utilizing the TCP/IP protocol suite to transmit data packets via packet switching.
APPLICATION LAYER
│ HTTP/HTTPS · DNS · FTP · SMTP · POP3 · IMAP · SSH
──────────────
TRANSPORT LAYER
│ TCP (Connection-Oriented) · UDP (Connectionless)
──────────────
INTERNET LAYER
│ IPv4 · IPv6 · ICMP · ARP · RARP · IPsec
──────────────
NETWORK ACCESS / LINK LAYER
│ IEEE 802.3 (Ethernet) · IEEE 802.11 (Wi-Fi)
Essential Internet Protocols & Port Numbers
| Protocol | Full Name | Port | Transport | Core Function |
|---|---|---|---|---|
| HTTP | Hypertext Transfer Protocol | 80 | TCP | Unencrypted web communication |
| HTTPS | HTTP Secure | 443 | TCP | Encrypted web (TLS/SSL) |
| DNS | Domain Name System | 53 | UDP/TCP | Domain → IP resolution |
| FTP | File Transfer Protocol | 20, 21 | TCP | File transfer (data + control) |
| SMTP | Simple Mail Transfer Protocol | 25, 587 | TCP | Sends/pushes email |
| POP3 | Post Office Protocol v3 | 110, 995 | TCP | Downloads email locally |
| IMAP | Internet Message Access Protocol | 143, 993 | TCP | Synchronizes email across devices |
| ARP | Address Resolution Protocol | — | Link | IP → MAC address mapping |
| DHCP | Dynamic Host Configuration Protocol | 67, 68 | UDP | Automatically assigns IP addresses |
| Telnet | Teletype Network | 23 | TCP | Remote terminal access (unencrypted) |
| SSH | Secure Shell | 22 | TCP | Secure remote terminal access |
Exam Tip: POP3 downloads and deletes emails from the server by default, whereas IMAP keeps emails on the server and synchronizes state across multiple devices.
2. Internet of Things (IoT) Architecture & Protocols
The Internet of Things (IoT) connects physical devices ("things") embedded with sensors, processing units, and software to network infrastructure, enabling machine-to-machine (M2M) data exchange without human intervention.
[ Layer 4: Application Layer ] → Smart Cities · Healthcare · Agriculture
──────────────
[ Layer 3: Middleware / Cloud ] → Cloud Analytics · Data Processing · Storage
──────────────
[ Layer 2: Network / Gateway ] → LoRaWAN · 6LoWPAN · Wi-Fi · Cellular
──────────────
[ Layer 1: Perception / Sensing ] → Sensors · Actuators · RFID · Cameras
Key IoT Communication Protocols
| Protocol | Model | Transport | Overhead | Typical Use |
|---|---|---|---|---|
| MQTT | Publish/Subscribe | TCP | Very Low | Smart homes, telemetry |
| CoAP | Client/Server (RESTful) | UDP | Low | Constrained smart devices |
| Zigbee | Mesh Topology | IEEE 802.15.4 | Low | Home automation |
| LoRaWAN | Star Topology | RF (Unlicensed) | Low | Smart city sensors (5–15 km) |
| 6LoWPAN | IPv6 Adaptation | IEEE 802.15.4 | Low | Low-power IPv6 networks |
MQTT = Message Queue · CoAP = Compact HTTP · Zigbee = Home Automation · LoRaWAN = Long Distance
3. Search Engine Architecture & Syntax
Search engines systematically index web pages to provide relevant query responses using three core phases:
CRAWLING → INDEXING → RANKING
Web spiders Parsing & Inverted Index PageRank / Relevancy
- Crawling: Automated bots ("spiders" like
Googlebot) parserobots.txtand follow hyperlinks to discover web pages. - Indexing: Extracted text is tokenized and stored in an Inverted Index (mapping words to Document IDs).
- Ranking: Algorithms like Google's PageRank and BM25 rank documents based on relevance, backlinks, and freshness.
High-Yield Search Operators
| Operator | Syntax Example | Function |
|---|---|---|
| Exact Match | "data structures notes" | Forces exact phrase matching |
| Site Filter | site:gov.in "syllabus" | Restricts search to a domain |
| Filetype | filetype:pdf computer networks | Returns files of specific extension |
| In-Title | intitle:"DBMS exam" | Matches pages with phrase in title |
| Exclusion | python -snake | Excludes pages containing the term |
4. Online vs Offline Messaging Architectures
ONLINE MESSAGING (Real-time)
Client ←— TCP / WebSocket —→ Server (Low Latency <100ms)
OFFLINE MESSAGING (Store & Forward)
Client → Save Local → Local DB → Sync on Net → Server
| Feature | Online Messaging | Offline Messaging |
|---|---|---|
| Network Link | Requires persistent connection | No connection needed while composing |
| Protocols | WebSockets, XMPP, MQTT | SMS (GSM MAP), SMTP, Outbox Queues |
| Delivery Model | Real-time push | Local storage → Background sync |
| Fault Tolerance | Breaks on network disconnect | Extremely high; buffers messages |
| Examples | WhatsApp, Telegram, Messenger | SMS Outbox, Draft emails, Offline queue |
5-Minute Quick Revision
5 Min
Internet & Protocols
- HTTP — Port 80 (Unencrypted)
- HTTPS — Port 443 (Encrypted)
- DNS — Port 53 (Domain → IP)
- FTP — Ports 20 (Data) & 21 (Control)
- SMTP — Port 25/587 (Send Email)
- POP3 — Port 110 (Download & Delete)
- IMAP — Port 143 (Sync across devices)
- ARP — IP → MAC | RARP — MAC → IP
- DHCP — Ports 67/68 (Auto IP assignment)
- SSH — Port 22 (Secure remote access)
5 Min
IoT & Messaging
- MQTT — Publish/Subscribe over TCP
- CoAP — RESTful over UDP
- Zigbee — IEEE 802.15.4, Home Automation
- LoRaWAN — Long Range (5–15 km)
- 6LoWPAN — IPv6 over low-power networks
- Online Messaging — Real-time, needs Internet
- Offline Messaging — Store & Forward, works offline
5 Min
Search Engines & Devices
- Crawling — Bots discover pages
- Indexing — Inverted Index (word → documents)
- Ranking — PageRank, BM25, Relevance
- Hub — Broadcasts to all devices
- Switch — Sends only to destination
- Router — Connects different networks
- Gateway — Connects different protocols
1-Minute Rapid Fire Revision
HTTP → 80
HTTPS → 443
DNS → 53
FTP → 20, 21
SMTP → 25, 587
POP3 → 110, 995
IMAP → 143, 993
ARP → IP→MAC
RARP → MAC→IP
DHCP → 67, 68
SSH → 22
Telnet → 23
MQTT → Pub/Sub, TCP
CoAP → REST, UDP
Zigbee → 802.15.4
LoRaWAN → Long Range
6LoWPAN → IPv6 + Low Power
Crawling → Discover
Indexing → Inverted Index
Ranking → PageRank
site: → Domain filter
filetype: → Extension filter
intitle: → Title filter
Hub → Broadcast
Switch → Destination only
Router → Different networks
Interactive MCQ Practice 50 Questions
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Quick Revision Checklist
- ✅ HTTP/HTTPS Ports: 80 (HTTP) vs 443 (HTTPS)
- ✅ Mail Protocols: SMTP (Send), POP3 (Download & Delete), IMAP (Sync)
- ✅ IoT Protocols: MQTT (Pub/Sub, TCP), CoAP (REST, UDP), 6LoWPAN (IPv6 on 802.15.4)
- ✅ Search Engine Stages: Crawling → Indexing (Inverted Index) → Ranking
- ✅ Network Layers: ARP at Link Layer; DNS at Application Layer
- ✅ Online vs Offline: Online needs active connection; Offline stores locally and syncs later
- ✅ Network Devices: Hub (broadcast), Switch (destination), Router (inter-network)
Master these concepts to score 8–15 marks in your exam. Good luck!