COMSATs Institute of Information Technology
Department of Electrical Engineering
QUIZ #1
Telecommunication System Engineering
Class: BET-6B
Q1: Explain Hybrid Function in telephone set?
5
Q2: Which electrical function are performed by telephone set, explain each step?
5
Q3: Write down the advantages of DTMF?
5
Q4: Write down the names of electronic switch types and what is the Custom Calling Features
of 5 ESS?
5
Q5: Draw PSTN switching hierarchy of North America and Pakistan?
5
SOLUTION OF QUIZ#2
Q1: Explain Hybrid Function in telephone set?
5
ANS: The hybrid circuit permits the interfacing of a 2-wire with a 4- wire system. Normal full-duplexex
Operations can still be maintained.
Windings C and E have their connections reversed from the connection of windings D and F. Therefore, the
voltage induced in winding G is opposite in phase to the voltage induced in winding H and opposes the voltage
in winding H. Since they are equal and opposite, they cancel each other.
The net result is that the signal from the transmitter that appears at terminals 7 and 8 is transmitted to
terminals 1 and 2, but does not appear at terminals 3 and 4 that go to the receiver.
Q2: Which electrical function are performed by telephone set, explain each step?
5
ANS:
1. Requests the use of the telephone system when the handset is lifted.
2. It indicates that the system is ready for use by receiving a tone, called the dial tone.
3. It sends the number of the telephone to be called to the system. This number is initiated by the caller
when the number is pressed (or the dial is rotated in older telephones).
4. It indicates the state of a call in progress by receiving tones indicating the status (ringing, busy, etc.).
5. it indicates an incoming call to the called telephone by ringing bells or other audible tones.
6. It changes speech of a calling party to electrical signals for transmission to a distant party through the
system. It changes electrical signals received from a distant party to speech for the called party.
7. It automatically adjusts for changes in the power supplied to it.
8. It signals the system that a call is finished when a caller “hangs up’’ the handset.
Q3: Write down the advantages of DTMF?
5
1. Decreases dialing time.
2. uses solid-state electronic circuits.
3. Can be used for end-to-end signaling after the call is connected.
4. Reduces local exchange equipment requirements.
5. It is more compatible with electronically (stored program) controlled data transmission), exchanges.
Q4: Write down the names of electronic switch types and what is the Custom Calling
Features of 5 ESS?
5
ANS: Names Of Electronic Switch Types:
1 ESS, 2 ESS, 3 ESS, 4 ESS, 5 ESS,
Custom Calling Features of 5 ESS:
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Call forwarding
Call waiting
Call Within
Speed Call code.
Three Way Calling
Call Trace
Caller ID
Caller ID Block
Q5: Draw PSTN switching hierarchy of North America and Pakistan?
North America:
Pakistan:
1,2,3
International Gateway Exchange
4
Transit Exchange/ Toll centre
5
Local Exchange /End office/ central office
5