Providing detailed answers to all 75 theory questions at once would result in an extremely long

response. To ensure clarity and readability, I will deliver the answers in structured batches (e.g.,
10–15 questions at a time), and compile them into a complete, organized document at the end if
needed.

Let's start with Theory Questions 1–10:

Q1: Explain different multiple access technologies in mobile

generation.

Answer: Multiple access technologies enable multiple users to share the same communication
channel:

 FDMA (Frequency Division Multiple Access): Divides spectrum

into distinct frequency bands for users.
 TDMA (Time Division Multiple Access): Assigns users separate
time slots within the same frequency.
 CDMA (Code Division Multiple Access): Assigns unique codes to
users, allowing simultaneous transmission.
 OFDMA (Orthogonal Frequency Division Multiple Access): Used
in LTE/4G, splits the channel into subcarriers for user allocation.
 SC-FDMA (Single Carrier-FDMA): A variant of FDMA used in LTE
uplink to reduce power consumption.

Q2: Classify and explain in brief the significance of different

logical channels for GSM.

Answer: Logical channels in GSM are classified into:

 Traffic Channels (TCH): Carry user data (voice or data).

 Control Channels (CCH):
o Broadcast Channels (BCH): Transmit system information (FCCH,
SCH, BCCH).
o Common Control Channels (CCCH): Manage call setup (RACH,
PCH, AGCH).
o Dedicated Control Channels (DCCH): Assigned to individual
mobiles (SDCCH, SACCH, FACCH).
Q3: Describe in brief the working of different Hard Handoff
mechanisms in GSM.

Answer: Hard handoff in GSM is a "break-before-make" process:

 Intra-cell Handoff: Switches frequency or time slot within the same

cell.
 Inter-cell, Intra-BSC: Transfers control to another cell under the
same BSC.
 Inter-BSC, Intra-MSC: Handoff between cells under different BSCs
but same MSC.
 Inter-MSC: Involves different MSCs, requiring coordination over
backbone networks.

Q4: Differentiate the following:

 Dedicated vs Associated Control Channels:

o Dedicated: Used only for a single user (e.g., SDCCH).
o Associated: Temporarily linked to a traffic channel (e.g., FACCH,
SACCH).

 Channel Allocation in GSM vs GPRS:

o GSM: Allocates fixed resources.
o GPRS: Uses dynamic resource allocation based on demand.

Q5: Draw GSM frame structure in detail and comment on each

frame.

Answer: GSM frame structure hierarchy:

 1 frame = 8 time slots (TDMA frame)

 26 TDMA frames = 1 multiframe (for traffic)
 51 TDMA frames = 1 control multiframe
 2048 multiframes = 1 hyperframe

Each frame carries specific types of channels and is synchronized using SCH and FCCH.
Q6: Explain step-by-step call setup process in GSM.

Answer:

1. MS sends RACH request.

2. BTS responds via AGCH.
3. SDCCH allocated for authentication, IMEI check.
4. TMSI assignment and ciphering.
5. BTS requests TCH from BSC.
6. Call established through MSC to PSTN/mobile.

Q7: What are different data services in GSM?

Answer:

 Circuit Switched Data (CSD)

 High-Speed Circuit Switched Data (HSCSD)
 Short Message Service (SMS)
 General Packet Radio Service (GPRS)
 Unstructured Supplementary Service Data (USSD)

Q8: With neat diagram explain transmission of short messages.

Answer: SMS path: MS → BTS → BSC → MSC → SMSC → Recipient MSC → Recipient
MS

The SMS is stored in the SMSC if the receiver is unavailable and sent when available.
Acknowledgment is also part of the process.

Q9: Describe the role of network blocks in the SMS service.

Answer:

 MS: Creates the message.

 BTS/BSC/MSC: Handle radio and switching.
 SMSC: Stores and forwards the message.
 HLR/VLR: Helps locate recipient MS.
Q10: Draw the architecture to explain HSCSD service.

Answer: HSCSD architecture includes:

 Multiple TCHs per user.

 Enhanced MSC and BSC for channel handling.
 Data terminal equipment (DTE) and Data circuit terminating
equipment (DCE) support higher data rates.

Would you like me to continue with Questions 11–20 now?

Here are the detailed answers for Theory Questions 11–20 from your mobile communication
question bank:

Q11: Draw the architecture to explain SMSCB service.

Answer: SMSCB (Short Message Service – Cell Broadcast) sends messages to multiple users
in a specific area.

Architecture:

 Cell Broadcast Entity (CBE): Creates message content.

 Cell Broadcast Center (CBC): Manages message scheduling and
distribution.
 BSC → BTS → MS: Delivers broadcast messages to all mobiles in a
cell.

Unlike SMS, it's one-to-many and doesn't depend on MS identity.

Q12: Draw and explain GSM GPRS service with network

architecture.

Answer: GPRS (General Packet Radio Service) adds packet-switched capabilities to GSM.

Architecture includes:

 MS (Mobile Station)
 BTS/BSC (Shared with GSM)
 SGSN (Serving GPRS Support Node): Manages session, mobility.
  GGSN (Gateway GPRS Support Node): Connects to external packet
networks (e.g., Internet).
 HLR/VLR: User profile and location info.

Data flows from MS → SGSN → GGSN → Internet.

Q13: Draw and explain GSM GPRS service with system

architecture.

Answer: The system architecture is similar to Q12 but highlights:

 GPRS core network elements (SGSN, GGSN)

 Interfaces: Gb (BSC to SGSN), Gn (SGSN to GGSN), Gi (GGSN to
Internet)
 Packet control units (PCUs) integrated into BSCs.

Q13 (alt): Classify and explain role of 3 radio channels added in

GPRS / Classify logical channels in GPRS

Answer: GPRS adds three radio channels:

 Packet Data Traffic Channel (PDTCH): For user data.

 Packet Associated Control Channel (PACCH): For control signaling
associated with PDTCH.
 Packet Timing Advance Control Channel (PTCCH): Adjusts timing
advance.

Logical Channels in GPRS:

 Packet Broadcast Control Channel (PBCCH)

 Packet Common Control Channel (PCCCH)
 Packet Data Channels (PDCHs)

Q14: Classify and explain GPRS coding schemes CS-1, CS-2, CS-3
and CS-4.

Answer: These schemes offer trade-off between data rate and reliability:

 CS-1: 9.05 kbps – Highest error protection.

  CS-2: 13.4 kbps – Medium protection.
 CS-3: 15.6 kbps – Less protection.
 CS-4: 21.4 kbps – Maximum speed, minimal protection.

Network chooses coding scheme based on signal conditions.

Q15: Explain in brief point-to-point & point-to-multipoint GPRS

services.

Answer:

 Point-to-Point (PTP): Between two devices, like mobile internet or

private messaging.
 Point-to-Multipoint (PTM): One sender, many recipients (e.g., group
alerts, news feeds).

PTM is used for multicast/broadcast services.

Q16: Explain with neat block diagram: TDMA, CDMA, OFDMA

Answer:

 TDMA: Time slots assigned to users. Efficient for moderate traffic.

 CDMA: Spreads signal over a wide frequency band using unique codes.
High capacity, secure.
 OFDMA: Subdivides bandwidth into subcarriers. Users assigned
subsets. Efficient for LTE/4G.

Each has a block diagram showing signal segmentation method.

Q17: Numericals on TDMA/CDMA/OFDMA

Answer: Numericals may include:

 TDMA: Time slot duration, number of users, bandwidth.

 CDMA: Processing gain, capacity, interference.
 OFDMA: Subcarrier spacing, data rate, spectral efficiency.

Note: Let me know if you want specific solved problems.

Q18: Write a brief note on GSM security mechanism.

Answer: GSM security provides:

 Authentication: Confirms user identity via A3 algorithm.

 Encryption: Voice/data encrypted using A5.
 Temporary identifiers: TMSI protects subscriber identity.

SIM stores key (Ki), used for authentication with network.

Q19: Explain A3, A5 and A8 algorithm for GSM security

mechanism.

Answer:

 A3: Authentication; uses Ki and RAND to generate SRES.

 A5: Encryption; uses Kc to cipher traffic between MS and BTS.
 A8: Key generation; derives ciphering key (Kc) from Ki and RAND.

These ensure authentication and secure communication.

Q20: Compare Voice and Data Traffic

Answer: | Aspect | Voice Traffic | Data Traffic | |--------|----------------|----------------| | Nature |

Real-time | Non-real-time | | Delay Tolerance | Low | High | | Bandwidth | Constant | Variable | |
Transmission | Continuous | Bursty | | QoS Sensitivity | High | Medium |

Voice requires low latency; data can tolerate delays but needs higher throughput.

Would you like me to proceed with Questions 21–30 next?

Here are the detailed answers for Theory Questions 21–30 from your mobile communication
question bank:
Q21: What are the advantages and disadvantages of Cellular
system?

Advantages:

 Efficient frequency reuse increases capacity.

 High coverage with low-power transmitters.
 Mobility support for users.
 Scalable architecture.
 Better spectrum utilization.

Disadvantages:

 Handoff complexity with mobility.

 Interference (co-channel, adjacent-channel).
 Cost of infrastructure for BTSs and MSCs.
 Limited coverage in remote areas.

Q22: State and explain different applications of mobile

communications.

Applications:

 Voice Communication: Calls via mobile networks.

 SMS/MMS: Text and multimedia messaging.
 Internet Access: Browsing, streaming, etc.
 Mobile Banking & Payments.
 Location-based Services (GPS).
 Healthcare: Telemedicine, patient tracking.
 IoT and Smart Cities.

Q23: Data transfer while roaming from GPRS network B to A

Answer:

1. MS is connected to SGSN_B and GGSN_A.

2. While roaming, tunneling is maintained via GGSN_A.
3. On returning to Network A:
o Old PDP context is updated.
o SGSN_A re-establishes session with GGSN_A.
o HLR updates the current SGSN.
 o Data transfer resumes seamlessly.

Q24: Find number of simultaneous communications per cell

Given:

 Uplink: 825–845 MHz = 20 MHz

 Downlink: 870–890 MHz = 20 MHz
 Duplex pair = 30 kHz/channel → 666 channels
 Reuse factors: 4, 7, 12, 19

Channels per cell = Total channels / Reuse factor

 For N=4 → 666/4 ≈ 166

 For N=7 → 95
 For N=12 → 55
 For N=19 → 35

Q25: Total communications with 16 cluster replications

Total capacity = Channels per cell × number of cells (in all clusters)

For each reuse factor (N):

 Cells = N × 16
 Total comms = (666/N) × (16 × N) = 666 × 16 = 10,656 (for all)

Conclusion: Capacity is same for all reuse factors, but interference differs.

Q26: Estimate number of users per system

Given:

 6 calls/day, 6 min/call → 36 mins/day = 0.025 Erlangs/user

 Total capacity = 666 × 16 = 10,656 Erlangs

Max users = 10,656 / 0.025 = 426,240 users

Q27: Area covered by each system (in cells)

Each cluster has N cells:

 N=4 → Area = 4
 N=7 → Area = 7
 N=12 → Area = 12
 N=19 → Area = 19

Q28: If 100 cells total, how many communications supported?

Channels per cell = 666/N Total channels = (100 × 666) / N

 N=4 → 16,650
 N=7 → 9,514
 N=12 → 5,550
 N=19 → 3,505

Q29: What happens if load increases in a cell?

Effects:

 Increased call blocking.

 Dropped calls due to failed handoffs.
 Interference increases, lowering signal quality.
 Network congestion causes slower data speeds.

Q30: Is it possible to have soft handoffs in GSM?

Answer: No, GSM uses hard handoff ("break-before-make") due to TDMA structure. Soft
handoff is used in CDMA, where a mobile can connect to multiple BTSs simultaneously.

Would you like me to continue with Questions 31–40 next?

Here are the detailed answers for Theory Questions 31–40:

Q31: Why do urban areas tend to have smaller cell sizes? How
does reuse ratio vary with rectangular cells?

Answer:

 Urban areas have:

o Higher user density → more traffic.
o More obstacles → weaker signal propagation.
o Therefore, smaller cells are needed to maintain capacity and
coverage.

Reuse Ratio with Rectangular Cells:

 In hexagonal cells: reuse ratio is .

 Rectangular cells are less efficient in coverage and create more
interference, reducing reuse flexibility.

Q32: Compare the generations of wireless communication.

Q33: Explain Co-channel and Adjacent channel interference and

how to reduce it?

Co-channel Interference:

 Occurs when same frequency is reused too close.

 Reduction: Increase reuse distance (D), use directional antennas.

Adjacent-channel Interference:

 From nearby frequency bands.

 Reduction: Use guard bands, proper filtering.

Q34: Describe Cell splitting and Cell sectoring techniques.

 Cell Splitting:
o Divides large cells into smaller ones to increase capacity.
o Requires more BTS installations.

 Cell Sectoring:
 o Uses directional antennas to split a cell into sectors (e.g.,
3×120°).
o Reduces interference, improves frequency reuse.

Q35: List out factors influencing small scale fading.

 Multipath propagation
 Speed of mobile
 Surrounding environment
 Carrier frequency
 Relative motion between transmitter and receiver

Q36: Explain small scale fading based on:

 Multipath Time Delay Spread:

o Delay between arrival of multipath components causes
intersymbol interference.

 Doppler Spread:
o Caused by relative motion.
o Leads to frequency shift → rapid signal fluctuations.

Q37: Explain Vocoder and its types.

Vocoder: Voice coder that compresses speech for transmission.

Types:

 Linear Predictive Coding (LPC)

 Code Excited Linear Prediction (CELP)
 Regular Pulse Excitation-Long Term Prediction (RPE-LTP) – used
in GSM
 Adaptive Multi-Rate (AMR) – used in 3G/4G

Q38: List criteria for selection of speech codecs for GSM.

 Low bit-rate
 High speech quality
  Low complexity
 Error resilience
 Compatibility with mobile channels
 Low processing delay

Q39: Write a brief note on Cell structure.

Answer: Cell structure refers to how coverage is divided:

 Hexagonal cells are idealized for frequency reuse.

 Each cell has a BTS and covers a region.
 Cells are arranged in clusters with reuse factor N.

Q40: Explain steps involved in call setup and call termination:

By Mobile:

1. Initiates call via RACH.

2. Receives AGCH.
3. Authentication and ciphering.
4. BSC allocates TCH.
5. Call established.

By Network:

1. Network locates MS via HLR/VLR.

2. Paging through BTS.
3. MS responds.
4. Call connected through MSC and TCH.

Would you like me to continue with Questions 41–50 next?

Here are the detailed answers for Theory Questions 41–50:

Q41: Explain Frequency Reuse concept in cellular networks and
state formula for N (Cells per cluster).

Answer: Frequency reuse allows the same frequency channels to be reused in different cells
separated by a certain distance to avoid interference.

 Reuse Factor (N): Number of cells in a cluster.

 Formula:

N = i^2 + ij + j^2

 Helps maximize capacity while minimizing interference.

Q42: Discuss Reflection and Diffraction propagation mechanisms.

 Reflection: Occurs when waves bounce off surfaces like buildings or

walls; dominant in urban environments.
 Diffraction: Bending of waves around obstacles like corners or sharp
edges; allows signal to reach beyond LOS.

Both are critical for non-line-of-sight communication.

Q43: Explain free space propagation model with formula.

Free Space Model describes how signal strength decreases over distance.

Formula:

P_r = \frac{P_t G_t G_r \lambda^2}{(4\pi d)^2 L}

 : Received power
 : Transmitted power
 : Gains of transmitter and receiver antennas
 : Wavelength
 : Distance between antennas
 : System loss
Q44: Classify small scale fading and explain Flat fading.

Types of Fading:

1. Flat fading: All frequencies of the signal fade equally.

2. Frequency selective fading: Only parts of the signal bandwidth fade.
3. Fast fading: Rapid signal changes due to Doppler effect.
4. Slow fading: Due to shadowing by large objects.

Flat fading occurs when signal bandwidth is less than the coherence bandwidth of the channel.

Q45: Received power and RMS voltage calculation

Given:

 Distance = 10 km, Power = 50 W

 Frequency = 900 MHz, , ,

Using Free Space Path Loss model:

P_r = \frac{P_t G_t G_r \lambda^2}{(4\pi d)^2}

Then use:

V_{rms} = \sqrt{P_r \times R}

A detailed numeric solution can be provided if needed.

Q46: Explain 2-ray model and one digital modulation technique.

2-Ray Model:

 Includes direct LOS path and ground-reflected path.

 Causes constructive and destructive interference.
 More accurate for medium to large distances.

Digital Modulation Example – QPSK:

 Quadrature Phase Shift Keying encodes 2 bits per symbol.

 Uses 4 phase shifts: 0°, 90°, 180°, 270°.
  Efficient for bandwidth and power.

Q47: What is the need for signaling? Classify them in detail.

Need:

 Control call setup, routing, billing, location update, handoff, etc.

Types of Signaling:

1. In-band: Shares the same path as voice.

2. Out-of-band: Separate path (e.g., SS7).
3. Line signaling: For line status.
4. Register signaling: For call-related data.

Q48: Brief note on signaling system in telecommunication.

Signaling System No. 7 (SS7):

 Out-of-band signaling protocol.

 Handles call setup, routing, SMS, roaming.
 Uses MTP, SCCP, TCAP layers.
 Enables fast and secure control signaling.

Q49: Draw and explain Time Slot hierarchy of GSM system.

Hierarchy:

 1 TDMA Frame = 8 time slots

 26 TDMA Frames = 1 Multiframe (Traffic)
 51 TDMA Frames = 1 Multiframe (Control)
 2048 multiframes = 1 Hyperframe

Used for scheduling, synchronization, encryption cycles.

Q50: Classify Handover. Explain Intra-cell and Intra-BSC Handover.

Types of Handover:
 1. Intra-cell: Change of channel within same cell.
2. Intra-BSC Inter-cell: Between different cells under the same BSC.
3. Inter-BSC Intra-MSC
4. Inter-MSC

Intra-cell: Used for quality improvement. Intra-BSC: Managed internally by BSC for load
balancing or coverage.

Would you like me to continue with Questions 51–60 next?

Here are the detailed answers for Theory Questions 51–60:

Q51: With neat diagram, explain the working of GSM full rate
speech encoder

Answer: The GSM Full Rate (FR) speech encoder uses RPE-LTP (Regular Pulse Excited –
Long Term Prediction) coding:

Components:

1. Pre-processing: Filters the speech signal.

2. LPC Analysis: Linear prediction coefficients are extracted.
3. Short-term analysis filter: Removes redundancies.
4. Long-Term Prediction (LTP): Exploits pitch periodicity.
5. RPE Encoding: Encodes residual signal.
6. Quantization: Converts to digital bits.

Output: 13 kbps compressed bitstream for transmission.

Q52: Compare Message switching, Packet switching and Circuit

switching techniques.

Q53: List out the requirements for 4G and 5G.

4G Requirements:

 All-IP network
 Min 100 Mbps (mobile), up to 1 Gbps (stationary)
  Low latency (~100 ms)
 OFDMA and MIMO support

5G Requirements:

 Data rates >10 Gbps

 Latency <1 ms
 Support for massive IoT
 Energy-efficient and ultra-reliable
 mmWave and beamforming technologies

Q54: Assumptions in Traffic Engineering

1. Pure-Chance Traffic: Call arrivals/terminations are random.

2. Statistical Equilibrium: Probabilities don’t change with time.
3. Full Availability: Any call can access any free trunk.
4. Lost Calls: Blocked calls are cleared immediately.

These simplify analysis of network performance.

Q55: Busy hour probability calculation

Given:

 3 calls made and 3 received/day

 Call duration = 2 mins
 Total usage = 6 calls × 2 = 12 mins = 0.2 Erlang

Using Erlang-B formula, probability depends on number of lines and offered load. If only 1
line:

P_{block} = \frac{A^1/1!}{\sum_{k=0}^{1} A^k/k!} = \frac{0.2}{1 + 0.2} = 0.167

So, ~16.7% chance of finding the line engaged.

Q56: Explain Blockage, Lost Calls, and Grade of Service (GoS)

 Blockage: When all trunks are busy, new calls can’t be connected.
 Lost Calls: Calls blocked and not retried.
  GoS: Measure of service quality.

GoS = \frac{\text{Blocked Calls}}{\text{Total Call Attempts}}

Q57: Queuing Systems – Erlang Distribution

 Erlang B: No waiting – blocked calls cleared.

 Erlang C: Calls wait in queue if all channels are busy.
 Erlang Distribution: Models call arrival and holding time as
exponential distributions.

Used to design and analyze telecom traffic.

Q58: Explain with neat diagram, Inter BSC and Inter MSC
Handover mechanism

Inter-BSC Handover:

 MS reports signal drop.

 Source BSC informs MSC.
 MSC coordinates with target BSC.
 Call control is transferred via MSC.

Inter-MSC Handover:

 Similar, but involves two MSCs.

 Requires exchange of signaling between MSCs.
 More complex due to different databases.

Q59: What is Doppler effect and explain 3 propagation

mechanisms.

Doppler Effect: Frequency shift due to relative motion between transmitter and receiver.

Propagation Mechanisms:

1. Reflection: Signal bounces off surfaces.

2. Diffraction: Signal bends around edges.
3. Scattering: Signal deflected by small objects → leads to fading.
Q60: Explain coherence bandwidth and small scale fading
methods.

 Coherence Bandwidth (Bc): Frequency range over which the

channel response is flat.

B_c \approx \frac{1}{2\pi \cdot \text{Delay Spread}}

 Diversity techniques (spatial, time, frequency)

 Equalization
 RAKE receiver
 Interleaving and coding

Shall I continue with Questions 61–70 next?

Here are the detailed answers for Theory Questions 61–70:

Q61: Explain in detail with neat diagram the working principles of

Time Division Switching.

Answer: Time Division Switching (TDS) connects calls by assigning time slots on a shared
medium.

Working:

 Input lines are sampled and digitized using PCM.

 Time Slot Interchange (TSI) rearranges time slots in memory.
 Output lines are formed by reading from memory in a new order.
 Efficient for digital traffic; used in digital exchanges.

Diagram includes:

 PCM Encoders/Decoders
 TSI Buffer
 Control Logic
Q62: Describe the significance of Grading.

Answer: Grading is the arrangement of switching paths to balance load and reduce blocking.

 Used when full availability is expensive.

 Two-stage or three-stage switches can be graded to ensure a
balance between cost and performance.
 Reduces the number of switches needed.

Q63: List and explore various Call Processing functions in

switching system.

Call Processing Functions:

1. Call setup: Dial tone, digit collection.

2. Routing: Choosing optimal path.
3. Charging: Duration and billing.
4. Call supervision: Monitoring status.
5. Call release: Clearing resources.
6. Traffic recording: Usage logs.

Q64: What is the need for synchronization in switching

techniques?

Answer:

 Prevents bit errors due to timing mismatch.

 Ensures frame alignment in TDM.
 Required for handover timing in mobile systems.
 Maintains network integrity during signal routing.

Q65: Explain Electronic Switching technique for voice traffic.

Answer:

 Uses digital techniques to route voice as PCM streams.

 Components include:
o Switching matrix
o Control unit
 o TSI buffer
 Supports multiplexing, signaling, and fault detection.
 Examples: SPC (Stored Program Control) and digital switches like
EWSD.

Q66: Write a short note on Common Channel Signaling (CCS).

Answer:

 CCS separates signaling from voice channels.

 Uses a dedicated signaling link (e.g., SS7).
 Enables fast call setup, authentication, SMS, roaming.
 More efficient than in-band signaling.

Q67: Explain with neat diagram LTE frame structure.

Answer: LTE Frame Structure:

 1 frame = 10 ms
 Divided into 10 subframes (1 ms each)
 Each subframe = 2 slots (0.5 ms)
 OFDM symbols per slot (7 normal, 6 extended CP)
 Carriers divided into Resource Blocks

Used for: Downlink scheduling, HARQ, reference signals.

Q68: List out opportunities and requirements of 5G technology.

Opportunities:

 Massive IoT
 Autonomous vehicles
 Smart cities
 Industrial automation
 AR/VR, ultra-HD streaming

Requirements:

 10 Gbps data rates

 <1 ms latency
  1 million devices/km²
 100× energy efficiency
 Support for mmWave bands

Q69: Draw open wireless architecture of 5G network.

Answer: Open Wireless Architecture includes:

 User Equipment (UE)

 NextGen RAN (gNBs)
 Core Network Functions (AMF, SMF, UPF)
 Network Slicing Layer
 Service-Based Interfaces
 MEC (Mobile Edge Computing)

Designed for flexibility and multi-vendor support.

Q70: What are different Radio transmission parameters in GSM

network?

Key Parameters:

 Frequency band: GSM-900, GSM-1800

 Channel spacing: 200 kHz
 Modulation: GMSK
 TDMA Frame: 8 time slots
 TCH bit rate: 13 kbps
 Transmission power levels: 0.8–20W

Used for planning and optimizing network performance.

Would you like me to proceed with the final set, Questions 71–75?

Here are the detailed answers for the final set — Theory Questions 71–75:
Q71: What is the significance of various interfaces in GSM
system?

Answer: Interfaces connect GSM subsystems for communication and control:

 Um: Between MS and BTS – radio interface.

 Abis: Between BTS and BSC – controls BTS and traffic.
 A: Between BSC and MSC – for signaling and voice/data.
 B: MSC to VLR – user location.
 C: HLR to VLR – user authentication and updates.
 D: MSC to HLR – call routing, location updates.
 E: MSC to MSC – inter-MSC handovers.
 F: MSC to EIR – equipment identity check.
 G: MSC to SMSC – SMS transfer.

Each ensures modular, scalable GSM network communication.

Q72: List various characteristics/standards of GSM 900 and GSM

1800

Q73: Describe with one block diagram, one GSM application.

Example Application: SMS Transmission

Block Diagram Includes:

 MS (Mobile Station)
 BTS → BSC → MSC
 SMSC (Short Message Service Center)
 HLR/VLR for routing and authentication
 Destination MS

Application Flow: SMS from user MS is routed via BTS/BSC/MSC to SMSC, which stores and
forwards it to the destination MS.

Q74: Compare Lost Call and Queuing Systems

Q75: Draw and calculate switching elements required for 2-stage
and 3-stage networks.

2-Stage Network:

 Input-stage and output-stage switches

 Total elements = , where N = inputs, M = outputs

3-Stage Network:

 Input (N), Middle (K), Output (N)

 Total elements =

Design Goals:

 Balance between cost and non-blocking performance

 Optimize K for given N

A diagram includes input/output lines and interconnecting switches.

All 75 theory questions have now been answered.

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