(SEM VII) THEORY EXAMINATION 2024-25 OPTICAL NETWORK

OPTICAL NETWORK (KEC073) – COMPLETE SOLVED PAPER

Time: 3 Hours  Max Marks: 100
Instructions: Attempt all Sections

SECTION A (2 × 10 = 20 Marks)

Attempt all questions in brief

a) Stimulated Brillouin Scattering (SBS) vs Stimulated Raman Scattering (SRS)

b) Optical packet switching

Optical packet switching transmits data as packets entirely in the optical domain, enabling high-speed switching without optical–electrical–optical (OEO) conversion.

c) Mach–Zehnder interferometer for WDM

A Mach–Zehnder interferometer splits light into two paths, introduces phase differences, and recombines them to separate or combine wavelengths for WDM systems.

d) Principle of operation of optical couplers

Optical couplers split or combine optical power between waveguides based on evanescent field coupling, conserving total optical energy.

e) ATM Adaptation Layer (AAL) function

AAL converts higher-layer data into ATM cells, handling segmentation, reassembly, and QoS support.

f) QoS management in IP networks               QoS is managed using:

Traffic prioritization                                        Packet scheduling

Bandwidth reservation                                   Congestion control

g) Lightpath topology design in WDM

It determines how optical paths are established between nodes, affecting routing efficiency, wavelength utilization, and blocking probability.

h) Wavelength Division Multiplexing (WDM)

WDM allows multiple optical signals at different wavelengths to be transmitted simultaneously over a single fiber, increasing capacity.

i) Synchronization in OTDM systems

Synchronization is achieved using optical clock recovery and timing alignment to ensure correct demultiplexing of high-speed data streams.

j) Optical vs electronic switching

SECTION B (10 × 3 = 30 Marks)

Attempt any three

a) Second-generation optical networks

Second-generation networks support packet-based transmission and higher bit rates. Optical packet switching reduces latency and improves bandwidth utilization compared to first-generation circuit-switched networks.

b) Optical couplers & energy conservation

Optical couplers distribute power between outputs. Energy is conserved as the sum of output powers equals input power minus losses.

c) SONET/SDH vs ATM

d) Lightpath topology & RWA

Topology design determines available routes, while Routing and Wavelength Assignment (RWA) selects paths and wavelengths, affecting blocking and performance.

e) Synchronization in optical networks

Synchronization ensures accurate timing, essential for OTDM to avoid inter-symbol interference and data loss.

SECTION C (10 × 5 = 50 Marks)

Attempt one from each question

Q3(a) Transmission basics in optical networks

Wavelength (λ): Determines channel identity             Frequency (f): Related to wavelength (f = c/λ)

Channel spacing: Minimum separation to avoid crosstalk
Used in dense WDM systems for high capacity.

Q3(b) Nonlinear effects in optical networks

Self-Phase Modulation (SPM): Signal phase changes due to its own intensity

Cross-Phase Modulation (XPM): Phase change caused by neighboring channels
These effects distort signals and limit system performance.

Q4(a) Optical filters comparison

Fabry–Perot filters                                                       Fiber Bragg gratings

Thin-film filters                                                            They differ in selectivity, bandwidth, and tunability.

Q4(b) Crosstalk impact & minimization

Crosstalk degrades signal quality.
Minimized by:                                                              Proper wavelength spacing

Directional isolation                                                     Improved filtering

Q5(a) ATM in optical networks & QoS

ATM uses fixed-size cells and AALs for segmentation. QoS ensures low delay, low jitter, and guaranteed bandwidth.

Q5(b) IP routing, forwarding & QoS

Routing determines paths; forwarding moves packets. QoS improves performance using traffic shaping and prioritization.

Q6(a) Wavelength assignment challenges

Limited wavelengths                                                     Scalability issues

Dynamic traffic patterns                                                These increase blocking probability.

Q6(b) Cost trade-offs in WDM design

Cost depends on:                                                           Network topology

Wavelength reuse                                                          Switching equipment
Efficient reuse reduces cost while maintaining performance.

Q7(a) Optical burst switching (OBS)

OBS aggregates packets into bursts sent optically.
Challenges: Burst loss, synchronization, control complexity.

Q7(b) OBS in MANs (feasibility)

Benefits: High bandwidth, low latency                        Challenges: Cost, burst contention, lack of buffering
Feasible for high-traffic metro networks with proper control.