all 22 MOST IMPORTANT & REPEATED QUESTIONS written in very simple, exam-oriented ESSAY answers.

 

⭐ UNIT 1 – Networking Basics

1. CIDR – Concept & Advantages

Concept

CIDR (Classless Inter-Domain Routing) is a method of IP addressing that removes the old Class A/B/C system.
It represents addresses as IP/prefix, for example:
192.168.1.0/24
Here, /24 means first 24 bits are network bits.

CIDR groups many IP networks into a single bigger block to reduce routing entries.

Advantages

  • Saves IP address space

  • Reduces routing table size

  • Supports flexible subnetting

  • Better Internet scalability

  • Allows variable-length subnet masks (VLSM)

  • Efficient address allocation

2. Subnetting & Supernetting – Simple Explanation

Subnetting

Subnetting divides one large network into many smaller networks.
Example: Dividing 192.168.1.0/24 into four /26 subnets.

Advantages:

  • Better security

  • Reduces broadcast traffic

  • Efficient IP usage

Supernetting

Supernetting combines multiple small networks into one larger network.
Example: Combine 4 networks:
200.1.0.0
200.1.1.0
200.1.2.0
200.1.3.0 → becomes 200.1.0.0/22

Advantages:

  • Reduces routing table entries

  • Useful for ISPs

  • Easier route summarization

3. IPv4 vs IPv6 – Differences

IPv4

  • 32-bit address

  • About 4.3 billion addresses

  • Dot decimal format

  • No built-in security

  • Manual or DHCP configuration

  • Example: 192.168.1.1

IPv6

  • 128-bit address

  • Almost unlimited addresses

  • Hexadecimal format

  • Built-in IPsec security

  • Auto configuration supported

  • Example: 2001:db8::1

4. Routers vs Bridges + Internet Explanation

Routers

  • Operate at Layer 3

  • Use IP addresses

  • Connect different networks

  • Support routing & forwarding

  • Main device used in the Internet

Bridges

  • Operate at Layer 2

  • Use MAC addresses

  • Connect two LAN segments

  • Reduce collision domains

Internet

Internet is a global network of networks where millions of devices use TCP/IP protocol to communicate.
It provides services like email, web, file transfer, video, cloud etc.

⭐ UNIT 2 – Routing + Transport Layer

5. OSPF – Working + Messages

Working

OSPF is a link-state routing protocol.
Each router discovers its neighbors and sends Link-State Advertisements (LSAs).
All routers build the same network map and use Dijkstra's Shortest Path First algorithm to compute the best path.

OSPF Messages

  1. Hello – Neighbor discovery

  2. DBD – Summary of database

  3. LSR – Request missing LSAs

  4. LSU – Send LSAs

  5. LSAck – Acknowledge LSUs

6. BGP – Characteristics

  • Path Vector protocol

  • Works between Autonomous Systems (AS)

  • Uses attributes like: AS-PATH, NEXT-HOP, LOCAL-PREF

  • Highly scalable – used by all ISPs

  • Supports policy-based routing

  • Ensures loop-free routing

  • Convergence is slow

  • Backbone protocol of the Internet

7. Silly Window Syndrome – Cause + Solutions

Cause

  • Receiver reads data very slowly

  • Sends very small window sizes

  • Sender transmits many tiny packets

  • Waste of bandwidth & overhead

Solutions

  • Nagle’s Algorithm (Sender)
    Combines small packets and sends them together.

  • Clark’s Solution (Receiver)
    Sends window updates only when its buffer is half-empty.

8. TCP vs UDP – Format + Features

TCP

  • Connection-oriented

  • Reliable, ordered delivery

  • Provides error control, congestion control

  • Packet called: Segment

  • Header contains: Seq no, Ack no, ports, flags, window size

UDP

  • Connectionless

  • No reliability

  • Very fast

  • Used in gaming, VoIP, video streaming

  • Packet called: Datagram

  • Header contains: ports, length, checksum

9. TCP Window Size Problem

If RTT = 300 ms and link is 2 Mbps, sender must increase window size to fully use network capacity.

Formula:
Window Size = Bandwidth × RTT

Used in numerical questions.

⭐ UNIT 3 – WLAN + Mobile IP + Ad-hoc

10. Hidden, Exposed, Near–Far Terminal Problems

Hidden Terminal

A & C can’t hear each other → both send to B → collision.

Exposed Terminal

C hears B → assumes medium busy → but can send to D → unnecessary delay.

Near–Far Problem

Near node’s strong signal hides far node’s weak signal.

11. Issues in Designing MAC Protocol for Ad-hoc Networks

  • No central controller

  • Dynamic topology

  • Energy constraints

  • Hidden & exposed node problems

  • Limited bandwidth

  • Security issues

  • Node mobility

12. Mobile IP – Key Definitions

  • Mobile Node (MN): Device that moves

  • Home Network: Original network of MN

  • Home Agent (HA): Keeps MN’s location

  • Foreign Network: New network MN visits

  • Foreign Agent (FA): Helps MN in foreign network

  • Care-of Address (CoA): Temporary IP in foreign network

  • Correspondent Node (CN): Communicating device

13. Ad-hoc Routing Protocols (AODV, DSDV, DSR, ZRP)

AODV

  • On-demand

  • Uses RREQ, RREP, RERR

  • Uses sequence numbers

DSDV

  • Table-driven

  • Uses sequence numbers

  • Avoids loops

DSR

  • On-demand

  • Source routing → full path in packet

ZRP

  • Hybrid

  • Proactive inside zone

  • Reactive outside zone

14. WLAN / IEEE 802.11 Architecture

  • BSS: One AP + stations

  • ESS: Multiple BSS connected

  • Supports roaming

  • MAC layer handles RTS/CTS, fragmentation, security

  • PHY layer uses DSSS/OFDM

⭐ UNIT 4 – Mobile Transport + GSM

15. I-TCP, S-TCP, M-TCP

I-TCP

Split connection into two parts at FA.
Wireless errors hidden from fixed network.

S-TCP

FA snoops packets and performs local retransmission.

M-TCP

Freezes TCP window during disconnection.

16. Handover / Handoff + Types

Types

  • Intra-BTS – frequency change within same cell

  • Inter-BTS (intra-BSC) – tower change

  • Inter-BSC (intra-MSC) – controller change

  • Inter-MSC – between different MSCs

17. GSM Architecture

  • MS: Mobile device

  • BSS: BTS & BSC

  • NSS: MSC, HLR, VLR, AUC, EIR

  • OSS: Network management

18. Cellular Network Architecture

Includes:
Cells → BTS → BSC → MSC → PSTN/Internet
Supports frequency reuse, handover, roaming.

⭐ UNIT 5 – Mobile OS + M-Commerce

19. Mobile Operating System (Android / iOS)

Android

  • Linux-based, open source

  • Java/Kotlin

  • Customizable UI

  • Google Play Store

iOS

  • Closed-source

  • Very secure

  • Swift/Obj-C

  • Used in iPhone/iPad

20. Software Development Kit (SDK)

SDK includes:

  • Tools

  • Libraries

  • Emulator

  • Debugger

  • Documentation

Android → Android Studio
iOS → Xcode

21. M-Commerce – Structure + Pros + Cons

Structure

Mobile device → Wireless network → App server → Database → Payment gateway

Pros

  • Convenient

  • Fast

  • Global reach

  • Lower cost

Cons

  • Security issues

  • Network dependence

  • Compatibility issues

22. Special Constraints of Mobile OS

  • Small screen

  • Low RAM/CPU

  • Limited battery

  • Unstable network

  • Security threats

  • Simple UI needed

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