About this previous year paper
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)
| SBS | SRS |
|---|---|
| Occurs due to acoustic phonons | Occurs due to optical phonons |
| Narrow bandwidth | Wide bandwidth |
| Limits power in single-channel systems | Enables optical amplification |
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
| Optical Switching | Electronic Switching |
|---|---|
| Very high speed | Limited speed |
| Low latency | Higher latency |
| Expensive | Mature and cheaper |
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
| SONET/SDH | ATM |
|---|---|
| Synchronous | Asynchronous |
| Fixed bandwidth | Variable bandwidth |
| Used for transport | Used for data & multimedia |
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.