(SEM V) THEORY EXAMINATION 2024-25 ELECTRONICS SWITCHING

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Subject Code: BEC055
Maximum Marks: 70
Time: 3 Hours
Paper ID: 310334

Question Paper Overview

SECTION A (2 × 7 = 14 Marks)

(Short-answer questions testing conceptual understanding of switching systems and networks)

a. Examine the significance of distribution frame in the Strowger System.
b. Describe the reed relay system.
c. Explain the graded rectangular switching matrix.
d. Define traffic intensity.
e. Define in-band and out-of-band signaling.
f. Explain the Banyan switch.
g. Describe flow control.

SECTION B (Attempt any three × 7 = 21 Marks)

a. Analyze general trunking with a neat sketch.
b. Analyze folded four-wire switches with their advantages.
c. Analyze mathematical modeling of switching systems.
d. Illustrate inter-register signaling.
e. Examine ATM cells with header format.

SECTION C (Attempt one part from each question × 7 = 35 Marks)

(a) Analyze the crossbar switch and diagonal crosspoint switch with a neat sketch.
OR
(b) Analyze various switching functions.

(a) Examine blocking and non-blocking three-stage networks.
OR
(b) Examine TST (Time-Space-Time) and STS (Space-Time-Space) switching with neat sketches.

(a) Derive the equation for Lost Calls Cleared (LCC) system with infinite sources.
OR
(b) Derive the Birth-Death process with a neat sketch.

(a) Illustrate PCM signaling and FDM in-band signaling.
OR
(b) Illustrate the Reliability, Availability, and Security (RAS) system.

(a) Illustrate the TCP/IP header cell.
OR
(b) Illustrate dynamic routing and fixed path routing protocols.

Key Topics for Revision

1. Strowger System

Early electromechanical switching system using step-by-step selectors.

Distribution frame: Connects subscriber lines to switching equipment, ensuring flexible wiring management and fault isolation.

2. Reed Relay System

Electromechanical switching with magnetic reeds enclosed in glass.

Faster and more reliable than Strowger switches.

Used in crossbar and hybrid digital exchanges.

3. Graded Rectangular Switching Matrix

Used for connecting large networks efficiently.

Graded matrix: Divides switches into smaller groups to minimize blocking probability.

Common in time-division multiplexed (TDM) systems.

4. Traffic Intensity

Definition: Average number of calls or circuits occupied in an hour.

A=λ×hA = \lambda \times hA=λ×h

where λ\lambdaλ = call arrival rate, hhh = average call holding time.

Unit: Erlang.

Represents load on a switching system.

5. In-Band and Out-of-Band Signaling

Type	Description	Example
In-Band	Control info (e.g., dial tones) sent over the same channel as voice data	DTMF tones
Out-of-Band	Separate channel for control info	Common Channel Signaling (CCS), SS7

6. Banyan Switch

Multistage interconnection network (MIN) used in packet-switched systems.

Self-routing property — data follows binary destination tags.

Used in ATM, parallel computing, and broadband ISDN.

7. Flow Control

Regulates data transmission between sender and receiver.

Prevents buffer overflow and congestion.

Methods: Stop-and-wait, Sliding window, Token passing.

8. General Trunking

Connects multiple local exchanges via trunks (high-capacity lines).

Optimizes resource sharing and reduces blocking probability.

9. Folded Four-Wire Switch

Uses four-wire circuits (two for transmit, two for receive).

Offers high-quality duplex transmission with reduced crosstalk.

Common in long-distance telephony and exchanges.

10. Mathematical Modeling of Switching Systems

Models traffic and performance using Markov chains or Poisson processes.

Helps determine blocking probability, queue length, and call setup delay.

11. Crossbar and Diagonal Crosspoint Switch

Crossbar Switch: Matrix of crosspoints connecting inputs and outputs directly.

Diagonal Crosspoint: Reduced complexity design; used in multistage switching networks.

12. Blocking and Non-Blocking Networks

Type	Description	Example
Blocking	Paths may be unavailable during busy conditions	Folded 3-stage network
Non-Blocking	All paths always available	Clos network (logically complete connection matrix)

13. TST & STS Switching

TST (Time-Space-Time): Combines time and space multiplexing to reduce hardware cost.

STS (Space-Time-Space): Used in fully digital systems for efficient switching.

14. Lost Calls Cleared (LCC) System

Assumes blocked calls are lost and cleared from the system.

Used in Erlang B formula:

B=ANN!∑k=0NAkk!B = \frac{\frac{A^N}{N!}}{\sum_{k=0}^N \frac{A^k}{k!}}B=∑k=0Nk!AkN!AN

where B = blocking probability, A = traffic load, N = number of circuits.

15. Birth-Death Process

Used to model call arrivals and departures.

Governed by Poisson arrival rate (λ) and exponential service rate (μ).

Represents system states as transitions between births (arrivals) and deaths (departures).

16. PCM and FDM Signaling

Technique	Function	Example
PCM (Pulse Code Modulation)	Converts analog voice into digital pulses	Digital telephony
FDM (Frequency Division Multiplexing)	Multiple signals transmitted using separate frequency bands	Analog carrier systems