5. Concept of Computer Network and Network Security System (ACtE05)

Computer Engineering (Nepal Engineering Council) – Engineering Licence Exam

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MCQ Questions

Comprehensive Study Guide for NEC License Exam - Computer Engineering

5. Concept of Computer Network and Network Security System (ACtE05)

Introduction

The Nepal Engineering Council (NEC) License Exam is a mandatory requirement for Computer Engineering graduates in Nepal to register as professional engineers. The section 5. Concept of Computer Network and Network Security System (ACtE05) tests knowledge of computer networking principles, protocols, architectures, and security mechanisms. These topics are critical for designing, managing, and securing modern network systems. This comprehensive note covers all subtopics (5.1 to 5.6) with detailed explanations, code examples (where applicable), diagram names, and exam-focused strategies to ensure students can rely on it for thorough preparation. The exam consists of 100 multiple-choice questions (MCQs), with 10 marks allocated to this section, requiring a 50% passing threshold and no negative marking.

The syllabus includes:

  • 5.1 Introduction to computer networks and physical layer (ACtE0501)
  • 5.2 Data link layer (ACtE0502)
  • 5.3 Network layer (ACtE0503)
  • 5.4 Transport layer (ACtE0504)
  • 5.5 Application layer (ACtE0505)
  • 5.6 Network security (ACtE0506)

5.1 Introduction to Computer Networks and Physical Layer (ACtE0501)

Key Concepts

Networking Model: Framework for communication (e.g., layered architectures).

Protocols and Standards: Rules for data exchange (e.g., IEEE, IETF standards).

OSI Model: Seven layers—Physical, Data Link, Network, Transport, Session, Presentation, Application.

TCP/IP Model: Four layers—Link, Internet, Transport, Application; maps to OSI.

Networking Devices:

  • Hubs: Layer 1, broadcast data to all ports.
  • Bridges: Layer 2, connect LAN segments using MAC addresses.
  • Switches: Layer 2, forward frames based on MAC tables.
  • Routers: Layer 3, route packets using IP addresses.

Transmission Media:

  • Wired: Twisted pair (e.g., Cat5e), coaxial, fiber optic.
  • Wireless: Radio waves, microwaves, infrared.

Diagram Names

  • OSI Model Layer Diagram
  • TCP/IP Model Diagram
  • Network Device Topology Diagram

Common MCQ Areas

  • Functions of OSI and TCP/IP layers.
  • Differences between hubs, switches, and routers.
  • Characteristics of transmission media.

Practice Tips

  • Study “Computer Networking: A Top-Down Approach” by Kurose and Ross for networking basics.
  • Memorize OSI and TCP/IP layer functions and protocols.
  • Compare wired and wireless media (e.g., speed, cost, reliability).
  • Draw network topologies with hubs, switches, and routers.

Sample MCQs

  1. Which OSI layer handles physical transmission of bits?

    • a) Data Link
    • b) Network
    • c) Physical
    • d) Transport
    • Answer: c) Physical.

  2. A switch operates at which OSI layer?

    • a) Layer 1
    • b) Layer 2
    • c) Layer 3
    • d) Layer 4
    • Answer: b) Layer 2.

5.2 Data Link Layer (ACtE0502)

Key Concepts

Services: Framing, error control, flow control, access control.

Error Detection and Correction: Parity bit, CRC, Hamming code.

Flow Control: Stop-and-Wait, Sliding Window (Go-Back-N, Selective Repeat).

Data Link Protocols: HDLC, PPP.

Multiple Access Protocols: ALOHA, CSMA/CD, CSMA/CA, Token Passing.

LAN Addressing and ARP: MAC addresses (48-bit), ARP maps IP to MAC.

Ethernet: IEEE 802.3, frame format (preamble, destination/source MAC, payload, CRC).

IEEE Standards:

  • 802.3: Ethernet, CSMA/CD.
  • 802.4: Token Bus.
  • 802.5: Token Ring.

CSMA/CD: Carrier Sense Multiple Access with Collision Detection, used in Ethernet.

Wireless LANs: IEEE 802.11 (Wi-Fi), uses CSMA/CA.

PPP: Point-to-Point Protocol for direct links (e.g., ISP connections).

Wide Area Protocols: Frame Relay, ATM.

Diagram Names

  • Ethernet Frame Format Diagram
  • Sliding Window Protocol Diagram
  • ARP Operation Diagram

Common MCQ Areas

  • Error detection methods (e.g., CRC calculation).
  • Flow control protocols (e.g., Go-Back-N vs. Selective Repeat).
  • MAC addressing and ARP resolution process.

Practice Tips

  • Study “Computer Networking: A Top-Down Approach” by Kurose and Ross for data link layer concepts.
  • Practice CRC calculations for error detection.
  • Simulate ARP using Packet Tracer or Wireshark.
  • Compare CSMA/CD and CSMA/CA mechanisms.

Sample MCQs

  1. Which protocol uses CSMA/CD?

    • a) Token Ring
    • b) Ethernet
    • c) PPP
    • d) Wi-Fi
    • Answer: b) Ethernet.

  2. ARP is used to resolve:

    • a) IP to MAC
    • b) MAC to IP
    • c) IP to port
    • d) MAC to port
    • Answer: a) IP to MAC.

5.3 Network Layer (ACtE0503)

Key Concepts

Addressing: IPv4 (32-bit, e.g., 192.168.1.1), classful addressing (A, B, C, D, E).

Subnetting: Divides network into smaller subnetworks (e.g., 192.168.1.0/24 → two /25 subnets).

Routing Protocols:

  • RIP: Distance vector, hop count metric.
  • OSPF: Link-state, shortest path first.
  • BGP: Path vector, used for inter-AS routing.
  • Unicast/Multicast: One-to-one vs. one-to-many routing.

Routing Algorithms:

  • Shortest Path: Dijkstra’s algorithm.
  • Flooding: Sends packets to all neighbors.
  • Distance Vector: Bellman-Ford, based on hop count.
  • Link State: OSPF, builds topology map.

Protocols: ARP, RARP, IP (fragmentation, TTL), ICMP (ping, traceroute).

IPv6: 128-bit addresses, packet format (fixed header, extension headers), transition (tunneling, dual-stack), multicasting.

Diagram Names

  • IPv4 Packet Format Diagram
  • Subnetting Example Diagram
  • OSPF Routing Process Diagram

Common MCQ Areas

  • Subnetting calculations (e.g., number of hosts, subnet masks).
  • Differences between RIP, OSPF, and BGP.
  • IPv6 features and transition mechanisms.

Practice Tips

  • Study “Computer Networking: A Top-Down Approach” by Kurose and Ross for network layer concepts.
  • Practice subnetting (e.g., divide 192.168.1.0/24 into 4 subnets).
  • Trace routing paths using Dijkstra’s algorithm manually.
  • Compare IPv4 and IPv6 packet formats.

Sample MCQs

  1. A Class C network has a default subnet mask of:

    • a) 255.0.0.0
    • b) 255.255.0.0
    • c) 255.255.255.0
    • d) 255.255.255.255
    • Answer: c) 255.255.255.0.

  2. Which protocol uses link-state routing?

    • a) RIP
    • b) OSPF
    • c) BGP
    • d) ICMP
    • Answer: b) OSPF.

5.4 Transport Layer (ACtE0504)

Key Concepts

Transport Service: Reliable data delivery, end-to-end communication.

Transport Protocols: TCP (connection-oriented, reliable), UDP (connectionless, best-effort).

Port and Socket: Ports (16-bit, e.g., 80 for HTTP), sockets (IP:port pair).

Connection Establishment/Release: TCP 3-way handshake (SYN, SYN-ACK, ACK), 4-way termination (FIN, ACK).

Flow Control & Buffering: TCP uses sliding window to manage data flow.

Multiplexing & Demultiplexing: Multiple applications share transport layer (e.g., port-based).

Congestion Control: TCP algorithms (slow start, congestion avoidance, fast retransmit).

Diagram Names

  • TCP 3-Way Handshake Diagram
  • Sliding Window Flow Control Diagram
  • Congestion Control Phases Diagram

Common MCQ Areas

  • TCP vs. UDP characteristics.
  • Steps in TCP connection establishment and termination.
  • Congestion control mechanisms.

Practice Tips

  • Study “Computer Networking: A Top-Down Approach” by Kurose and Ross for transport layer concepts.
  • Draw TCP handshake and termination sequences.
  • Analyze Wireshark captures for TCP/UDP packets.
  • Study congestion control phases (e.g., slow start vs. congestion avoidance).

Sample MCQs

  1. TCP establishes a connection using:

    • a) 2-way handshake
    • b) 3-way handshake
    • c) 4-way handshake
    • d) No handshake
    • Answer: b) 3-way handshake.

  2. Which protocol is connectionless?

    • a) TCP
    • b) UDP
    • c) HTTP
    • d) FTP
    • Answer: b) UDP.

5.5 Application Layer (ACtE0505)

Key Concepts

Web: HTTP (port 80, request-response), HTTPS (port 443, secure).

File Transfer: FTP (port 21, control/data), PuTTY (SSH client), WinSCP (secure file transfer).

Electronic Mail: SMTP (port 25, send), POP3/IMAP (retrieve), MIME (attachments).

DNS: Resolves domain names to IP (e.g., www.example.com → 93.184.216.34).

P2P Applications: BitTorrent, peer-to-peer file sharing.

Socket Programming: Client-server communication using sockets (e.g., TCP/UDP sockets in C).

Application Server Concept: Hosts services (e.g., Apache, Nginx).

Traffic Analyzers: MRTG (traffic graphs), PRTG (monitoring), SNMP (network management), Packet Tracer (simulation), Wireshark (packet analysis).

Code Example

#include 
#include 
#include 
int main() {
    int sockfd = socket(AF_INET, SOCK_STREAM, 0); // TCP socket
    printf("Socket created: %d\n", sockfd);
    return 0;
}

Diagram Names

  • HTTP Request-Response Diagram
  • DNS Resolution Process Diagram
  • Client-Server Socket Communication Diagram

Common MCQ Areas

  • Port numbers for HTTP, FTP, SMTP, etc.
  • DNS query types and resolution steps.
  • Socket programming concepts.

Practice Tips

  • Study “Computer Networking: A Top-Down Approach” by Kurose and Ross for application layer protocols.
  • Write a simple TCP client-server program in C or Python.
  • Trace DNS resolution using nslookup or dig.
  • Analyze packets with Wireshark for HTTP and FTP.

Sample MCQs

  1. HTTPS uses port:

    • a) 80
    • b) 443
    • c) 25
    • d) 21
    • Answer: b) 443.

  2. DNS primarily resolves:

    • a) MAC to IP
    • b) Domain to IP
    • c) IP to MAC
    • d) Port to IP
    • Answer: b) Domain to IP.

5.6 Network Security (ACtE0506)

Key Concepts

Types of Computer Security: Confidentiality, integrity, availability (CIA triad).

Security Attacks: Passive (eavesdropping), active (DoS, MITM, spoofing).

Principles of Cryptography: Symmetric (e.g., AES, DES), asymmetric (e.g., RSA).

RSA Algorithm: Public/private key pair, based on prime factorization (e.g., C = M^e mod n).

Digital Signatures: Ensures authenticity using private key signing, public key verification.

Securing E-mail: PGP (Pretty Good Privacy) for encryption and signing.

Securing TCP Connections: SSL/TLS (handshake, encryption, e.g., HTTPS).

Network Layer Security: IPsec (AH, ESP), VPN (tunneling).

Securing Wireless LANs: WEP (weak, deprecated), WPA/WPA2 (secure).

Firewalls: Packet filtering, stateful inspection, application-layer gateways.

Code Example

# Simple RSA encryption (Python pseudocode)
def rsa_encrypt(message, e, n):
    return pow(message, e, n)  # C = M^e mod n
print(rsa_encrypt(5, 7, 143))  # Example: M=5, e=7, n=143

Diagram Names

  • RSA Encryption/Decryption Diagram
  • SSL/TLS Handshake Diagram
  • Firewall Architecture Diagram

Common MCQ Areas

  • Symmetric vs. asymmetric cryptography.
  • RSA algorithm steps and applications.
  • Firewall types and security protocols (e.g., IPsec, SSL).

Practice Tips

  • Study “Cryptography and Network Security” by William Stallings for security concepts.
  • Practice RSA encryption/decryption with small numbers (e.g., p=11, q=13).
  • Configure a simple VPN or firewall rule in a lab environment.
  • Compare WEP, WPA, and WPA2 security features.

Sample MCQs

  1. RSA is an example of:

    • a) Symmetric cryptography
    • b) Asymmetric cryptography
    • c) Hashing
    • d) Compression
    • Answer: b) Asymmetric cryptography.

  2. Which protocol secures wireless LANs?

    • a) WEP
    • b) WPA2
    • c) IPsec
    • d) SSL
    • Answer: b) WPA2.

General Preparation Strategies

  • Syllabus Review: Study the official NEC syllabus to focus on key networking and security topics.
  • Textbooks: Use “Computer Networking: A Top-Down Approach” by Kurose and Ross for networking, and “Cryptography and Network Security” by William Stallings for security.
  • Practice: Solve 20–30 MCQs per subtopic, focusing on subnetting, routing, and cryptography calculations.
  • Simulations: Use Packet Tracer for network design, Wireshark for packet analysis, and OpenSSL for cryptography experiments.
  • Time Management: Practice 10–15 MCQs in 12–15 minutes to match exam pace.

Conclusion

This comprehensive study guide covers all subtopics under 5. Concept of Computer Network and Network Security System (ACtE05) for the NEC License Exam, providing detailed explanations, code examples, diagram names, and practice strategies. Designed as a reliable resource for students, it ensures thorough preparation for networking principles, protocols, and security mechanisms. By mastering these topics and practicing MCQs, candidates can confidently excel in the exam.

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