PROGRAMME
MASTER OF COMPUTER APPLICATIONS (MCA)
SEMESTER
II
COURSE CODE & NAME
DCA6206 COMPUTER NETWORKS & PROTOCOLS
Section A
Multiple Choice Questions (2 Marks each)
[Please answer all the questions]
1. Identify the additional layers present in the OSI model that are not part of the TCP/IP model?
a) Application layer
b) Presentation layer
c) Session layer
d) Session and Presentation layer
2. Choose the option that accurately represents the core functionalities handled by the presentation layer.
a) Data compression
b) Data encryption
c) Data description
d) All of the mentioned
3. Select the option that is not typically performed by the network layer?
a) routing
b) inter-networking
c) congestion control
d) error control
4.
Determine which network topology mandates the use of a multipoint connection setup.
a) Star
b) Mesh
c) Ring
d) Bus
5. Recognize the type of switching used in a standard local telephone network.
a) Packet switched
b) Circuit switched
c) Bit switched
d) Line switched
6. Identify the layer of the OSI model where IPSec implements its security measures
a) Transport layer
b) Network layer
c) Application layer
d) Session layer
7. Choose the statement that incorrectly describes characteristics of the User Datagram Protocol (UDP)?
a) Connection-oriented
b) Unreliable
c) Transport layer protocol
d) Low overhead
8. Indicate the condition under which packet retransmission should be avoided
a) Packet is lost
b) Packet is corrupted
c) Packet is needed
d) Packet is error-free
9. Select the challenge associated with Fragmentation that impacts network reliability or efficiency?
a) Complicates routers
b) Open to DOS attack
c) Overlapping of fragments
d) All of the mentioned
10. Identify the specific protocol employed by OSPF to automatically detect neighboring routers?
a) Link state protocol
b) Error-correction protocol
c) Routing information protocol
d) Hello protocol
Section B
SHORT ANSWERS (5 Marks each)
[Please answer Any Four questions in a separate page answer sheet especially provided for this purpose]
1.
2.
3.
4.
Illustrate the structure and advantages of mesh topology within a computer network.
Describe the concept and operational process of virtual circuit switching in a packet-switched environment.
Outline the principal objectives considered during the design of SONET.
Identify various ISDN-compatible devices and elaborate on their specific functions within an ISDN-based
communication system.
5. Using an appropriate diagram, explain the structure and components of the X.25 protocol.
6. Present a concise explanation highlighting the role and mechanism of digital signatures in secure communication.
Section C
LONG ANSWERS (10 Marks each)
[Please answer Any Three questions in a separate page answer sheet especially provided for this purpose]
1. Distinguish between PAN, LAN, MAN, and WAN by describing each network type and illustrating with
relevant examples.
2. Elaborate on the internal working mechanism of the OSPF routing protocol and its significance in
dynamic routing.
3. Explain the feedback-based mechanisms used for preventing congestion in networks, along with the
nature of feedback data exchanged.
4. Define the concept of packet filtering and discuss its merits in the context of network security and
performance.
Section B — Short Answers (5 marks each)
(Paper says “any four”; I’m giving all six so you can choose.)
1) Mesh Topology: Structure & Advantages
Structure: Every node connects to every other node via dedicated links (full mesh) or selected neighbors (partial
mesh).
Advantages:
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High reliability/fault tolerance: Multiple alternative paths; a single link failure rarely isolates nodes.
Excellent performance: Dedicated links reduce collisions/contention.
Security: Point-to-point links limit eavesdropping scope.
Trade-offs: Expensive cabling/ports in full mesh; complex management. Partial mesh balances cost and
resilience.
2) Virtual Circuit Switching (in Packet-Switched Networks)
Establishes a logical path before data transfer. Phases: call setup (path + VC identifiers allocated), data transfer
(packets follow the VC in order), teardown. Each switch keeps state (VCID → outgoing port/VCID).
Pros: Ordered delivery, predictable QoS, simpler per-packet routing. Cons: Setup overhead, less flexible under
failures than pure datagrams. Examples include X.25 and Frame Relay styles.
3) SONET — Design Objectives
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Standardized optical hierarchy for multi-vendor interoperability.
High data rates with synchronous framing (STS/OC levels).
Robust protection switching (e.g., bidirectional line-switched rings with ~50ms recovery).
Network management via overhead bytes for OAM&P.
Flexible multiplexing (add/drop capability) and long-haul reach with low jitter.
4) ISDN Devices & Their Functions
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TE1 (Terminal Equipment 1): ISDN-native devices (ISDN phones, terminals).
TE2: Non-ISDN gear (PCs, analog phones) requiring adaptation.
TA (Terminal Adapter): Adapts TE2 to ISDN interface.
NT1 (Network Termination 1): Physical termination at customer site; line to S/T bus.
NT2: More advanced customer premises equipment (e.g., PBX) handling switching/concentration.
Interfaces: BRI (2B+D) and PRI (23/30B+D) for voice/data integration.
5) X.25: Structure & Components (with verbal diagram)
Layers:
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Physical: X.21/V.24 interfaces.
Link: LAPB (error/flow control, framing).
Network: Virtual circuits (PVC/SVC), call setup (CALL REQUEST/ACCEPT), sequencing, congestion
control.
Path: DTE ↔ DCE (PSE nodes) over a chain of packet switches using VC identifiers.
6) Digital Signatures: Role & Mechanism
Provide authentication, integrity, non-repudiation. Sender computes a hash of the message and signs it with
their private key; receiver verifies using the public key (often via a certificate/PKI). Protects against tampering
and impersonation; widely used in TLS handshakes, code signing, and secure email.
Section C — Long Answers (10 marks each)
(Paper says “any three”; I’m giving all four so you can pick.)
1) PAN vs LAN vs MAN vs WAN — Definitions & Examples
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PAN (Personal Area Network): ~1–10 m scope around a person; Bluetooth between a phone, earbuds,
smartwatch. Prioritizes low power and simplicity.
LAN (Local Area Network): Building/campus scope; Ethernet/Wi-Fi connecting PCs, printers, servers
via switches and APs. High bandwidth, low latency, private administration.
MAN (Metropolitan Area Network): City-scale backbones; metro Ethernet, DOCSIS access networks,
city-wide fiber rings. Aggregates many LANs with carrier-grade switching and protection.
WAN (Wide Area Network): National/global; MPLS, IP over SDH/SONET, long-haul fiber, satellite.
Connects distant sites, uses provider infrastructure and routing (e.g., BGP).
Key differences: geographic span, ownership (private vs carrier), technologies (Ethernet/Wi-Fi vs
optical/MPLS), and QoS/latency expectations. Example mapping: A company’s office LAN, city fiber
MAN to ISP PoP, and global WAN VPN between branches; an individual’s PAN links phone to
wearables.
2) How OSPF Works & Why It Matters
OSPF (Open Shortest Path First) is a link-state IGP for IP networks.
Mechanism:
1. Neighbor discovery: Routers send Hello packets on interfaces; matching parameters form adjacencies
and elect DR/BDR on multiaccess nets.
2. LSA flooding: Each router advertises Link-State Advertisements (router LSAs, network LSAs,
summary, external, etc.). Reliable flooding ensures a consistent Link-State Database (LSDB) per area.
3. Areas & hierarchy: Backbone Area 0 connects other areas; reduces LSDB size and limits SPF scope.
ABRs summarize routes between areas; ASBRs inject externals (E1/E2).
4. SPF calculation: Each router runs Dijkstra on its LSDB to compute shortest paths and populate the
routing table.
5. Convergence & metrics: Uses cost (often 10^8/bandwidth) and fast detection of changes (Hello/Dead
timers), yielding quick convergence.
Significance: Scales well via areas, supports VLSM, equal-cost multipath, authentication, and policy via
summarization—making it a staple dynamic IGP in enterprises and service providers.
3) Feedback-Based Congestion Control — Mechanisms & Feedback
Nature
Goal: Prevent persistent overload where demand exceeds network capacity.
End-to-end (implicit feedback): TCP congestion control infers congestion from packet loss, ECN marks, or
rising RTT. Algorithms (AIMD, Tahoe/Reno, CUBIC, BBR variants) adjust cwnd: slow start, congestion
avoidance, fast retransmit/recovery. Feedback is implicit (loss/delay) or explicit with ECN bits set by routers.
Network-assisted (explicit feedback): Routers signal senders:
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DECbit/ECN: Mark packets when queue exceeds thresholds; receivers echo marks to senders.
RED/CoDel: Active queue management drops/marks early to signal impending congestion.
Hop-by-hop flow control (e.g., credit-based in some L2 fabrics) provides precise backpressure.
Key ideas: Keep queues short (low latency), avoid global synchronization, ensure fairness (per-flow
management), and stabilize with control-theory-tuned parameters. Feedback data can be binary marks,
drop events, or quantitative credits/queue measures.
4) Packet Filtering — Concept & Merits
Concept: Examine packet headers (IP src/dst, ports, protocol, flags, interfaces) at routers/firewalls and apply
rules to permit/deny traffic. Implemented as stateless ACLs, stateful inspection (tracking connections), or nextgen policies with app awareness.
Merits:
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Security baseline: Blocks unwanted or spoofed traffic at the perimeter; enforces least exposure.
Performance: Lightweight compared to deep inspection; can be accelerated in hardware (TCAM/NPU).
Policy control: Enforces segmentation, ingress/egress controls, and compliance requirements.
Composability: Forms part of layered defense with NAT, IPS, proxies, and zero-trust segmentation.
Considerations: Stateless filters can’t validate session context; stateful filters require memory/CPU.
Good practice includes default-deny, explicit allows, logging, and periodic rule hygiene.
Section A — MCQs (2 marks each)
(All attempted.)
1. Session and Presentation layer
2. All of the mentioned
3. error control
4. Bus
5. Circuit switched
6. Network layer
7. Connection-oriented
8. Packet is needed (i.e., don’t retransmit if it’s already received/usable)
9. All of the mentioned
10. Hello protocol