About this previous year paper
Section A – Short answer type questions (2 marks each)
Section B – Long answer type questions (5 marks each)
Section C – Very long answer type questions (10 marks each)
Let’s begin with Section A first — detailed yet clear long explanations for each short question.
Then I’ll cover Section B and Section C one by one.
SECTION A — Short Answer Type Questions (Long Explanation Style)
Q1. What is a switching system?
A switching system is a network arrangement that establishes a communication path between two or more users. It automatically connects a call between subscribers by selecting a path through multiple switching elements.
There are two main types of switching systems:
Circuit Switching: A dedicated path is set up for the entire duration of communication (e.g., telephone networks).
Packet Switching: Data is divided into packets and sent through different routes (e.g., internet).
The switching system reduces the number of direct connections and enables efficient utilization of network resources.
Q2. Define traffic intensity.
Traffic intensity measures the load on a switching system and is defined as the average number of calls occupying resources (like trunks or servers) during a specific time.
A=λ×hA = \lambda \times hA=λ×h
Where:
λ\lambdaλ = average number of calls per unit time
hhh = average holding time per call
Traffic intensity is expressed in Erlangs (E).
1 Erlang = 1 circuit continuously occupied for 1 hour.
Q3. What is signaling?
Signaling refers to the exchange of information between switching centers or between subscribers and the network to establish, control, and release connections.
Types:
Subscriber Signaling: Between user and exchange (e.g., dial tone).
Inter-exchange Signaling: Between two exchanges (e.g., routing info).
Supervisory Signaling: Indicates call status (off-hook, on-hook).
Modern systems use Common Channel Signaling (CCS) like SS7 for fast and reliable message exchange.
Q4. Differentiate between analog and digital switching.
| Feature | Analog Switching | Digital Switching |
|---|---|---|
| Signal Type | Continuous | Discrete binary |
| Example | Crossbar, Strowger | PCM, TST, Time Switch |
| Noise | High | Low |
| Flexibility | Less | High |
| Transmission | Uses analog circuits | Uses digital time slots |
Digital switching is preferred today due to its high speed, reliability, and integration with data networks.
Q5. What is PCM and its importance?
PCM (Pulse Code Modulation) converts analog signals (like voice) into digital form for transmission.
Steps:
Sampling – converts continuous signal into discrete samples.
Quantization – approximates each sample to the nearest level.
Encoding – represents quantized levels as binary codes.
Importance:
High noise immunity Efficient multiplexing (TDM)
Easy digital processing Compatible with digital switching
Q6. What is the function of a concentrator?
A concentrator connects many subscriber lines to fewer trunks by exploiting the fact that not all users call simultaneously.
Functions:
Reduces hardware cost and wiring complexity.
Temporarily connects subscribers with available switching paths.
Used in local exchanges to improve efficiency.
Q7. What is meant by grade of service (GoS)?
Grade of Service is a measure of the quality of service of a telephone network, defined as:
GoS=Number of lost callsTotal offered calls\text{GoS} = \frac{\text{Number of lost calls}}{\text{Total offered calls}}GoS=Total offered callsNumber of lost calls
It indicates the probability that a call will be blocked due to lack of resources.
Typical acceptable GoS = 0.01 to 0.02 (1–2% blocking).
Q8. What is meant by space and time switching?
Space Switching: Physical connection is made through crosspoints between input and output lines (used in analog systems).
Time Switching: Uses time slots to interconnect signals digitally using TDM (Time Division Multiplexing).
Hybrid Switch = Time-Space-Time (TST) configuration for large digital exchanges.
Q9. Define Echo and its effects.
Echo is the reflection of transmitted voice signals caused by impedance mismatch in the circuit.
Effects:
Causes speech distortion.
Leads to delay and poor quality in long-distance calls.
Solution: Use echo suppressors or echo cancellers in digital systems.
Q10. What is an Intelligent Network (IN)?
An Intelligent Network (IN) is a telecommunications architecture that separates service logic from the switching function.
It allows operators to introduce new services (like prepaid, toll-free numbers, call forwarding) without changing switch hardware.
Key Components:
Service Switching Point (SSP) Service Control Point (SCP) Service Management System (SMS)