1. TELEPHONE INSTRUMENTS & SIGNALS
Copy of the original phone of Graham Bell at the Musée des Arts et Métiers in Paris
1896 Telephone (Sweden)

2. INTRODUCTION Communication Components
The process of conveying information from one place to another
Components
Source of information
Transmitter
Receiver
Destination
Transmission medium

3. Telecommunication Telephone A long distance communications
‘tele’ Greek word for distant or afar
Telephone
One of the most remarkable devices ever invented

4. Originally developed for conveying human speech information (voice)
Now extensively used to transport data using data modems
PTN
Public telephone network
Global communications network

5. Rapid Development of Telephone System
Alexander Graham Bell & Thomas A Watson invented the telephone
1877 – there are only 6 telephones in the world
1881 – 3,000 telephones
1883 – 133,000 (in US)

6. Telecommunication Giant Evolution
AT&T –American Telephone & Telegraph Company
Referred to as the Bell Telephone System
In $155 billion assets, 1M employees, 100,000 vehicles
Comparison with Microsoft assets in 1988
$10 billion
1.5 billion telephone sets are operating in the world today

7. The Subscriber Loop POTS – Plain Old Telephone Service
Simplest and most straightforward form of telephone service
Involves subscribers accessing the PTN through a pair of wires called the local subscriber loop (or simply local loop)

8. The Subscriber Loop Local Loop
Most fundamental component of a telephone circuit
Unshielded twisted pair(UTP) transmission line
Cable pair – 2 insulated conductors twisted together

9. The Subscriber Loop
Comprised of several lengths of copper wire interconnected at the junction & cross connect boxes located in manholes.
Provides the means to connect telephone set of the subscriber’s location to the closest telephone office
A telephone office – end office/local exchange/central office
Connected to an electronic switching system (ESS)
Enables the subscriber to access the PTN (will be discussed later)

10. Standard Telephone Set
Telephone – ‘tele’ – from afar, phone – sound/ voice
An apparatus for reproducing sound, especially that of the human voice (speech) at a great distance by means of electricity; consisting of transmitting & receiving instruments connected by a line or wire which conveys the electric current

11. Standard Telephone Set
Basic telephone set
Simple analog transceiver designed for converting speech of acoustical signals to electrical signals
Added features: multiple line selection, hold, caller ID

12. Standard Telephone Set
Butterstamp telephone(1878)
First telephone set that combined a transmitter and receiver into single handheld unit
Rotary Dial Telephone
Introduced by western electric company also called the bell system
Touch-Tone Telephone

14. Quality of Transmission
Depends on
the received volume
Frequency response of the telephone circuit
Degree of the interference

15. Functions of the Telephone Sets
Notify the subscriber when there is an incoming call with an audible signal – bell or visible signal – flashing light
Provide a signal to a telephone network verifying when the incoming call has been acknowledged & answered
Receiver is lifted off hook
Convert speech energy to electrical energy (Tx) and vice versa (Rx)
Microphone, Speaker

16. Functions of the Telephone Sets
Incorporate some method of inputting and sending destination telephone numbers
From tel. Sets to central office
‘pulses’ rotary dialer
‘frequency tones’ touch tone
Regulate the amplitude of the speech signal
To avoid crosstalk
Notify the tel. Office when a subscriber wishes to place an outgoing call (handset lifted off hook)
Dial tone

17. Functions of the Telephone Sets
Ensure that a small amount of the transmit signal is fed back to the speaker
Feedback signal- sidetone/talkback
Provide an open circuit (idle condition) to the local loop when the telephone is not in use (on hook)
Closed ckt – busy (off hook)
Provide a means of transmitting & receiving call progress signals between the central office switch & the subscriber
On & off hook signal, busy, ringing, dial tone

18. Components of a Telephone Sets
Transmitter
Receiver
Electrical network for equalization
Associated circuitry
to control sidetone level
to regulate signal power
Signaling circuitry

19. Essential Components Ringer Circuit On/Off Hook Circuit
Electronic oscilllator
To alert the destination party of the incoming calls
On/Off Hook Circuit
Simple single throw-double-pole STDP switch
Placed across the ‘tip’ and ‘ring’
On hook (idle, open switch), off-hook (in use, closed switch)

20. Essential Components Equalizer circuit Speaker/receiver
Combination of passive components (resistors & capacitors)
To regulate the amplitude & frequency response of the voice signals
Speaker/receiver
Converts electrical signals received from the local loop to acoustical signals (sound waves)
Enclosed in the handset of the telephone along with a microphone

21. Essential Components Microphone Hybrid network Transmitter
Converts acoustical signals in the form of sound pressure waves from the caller to electrical signals
Hybrid network
Hybrid coil/duplex coil
Special balanced transformer used to convert 2-wire (local loop) circuit into 4-wire (telephone set) circuit
Outgoing signal –1 to 2V, incoming – half of outgoing signal

22. Essential Components Dialing circuit
Enables the subscriber to output signals representing digits
Rotary dialer/Electronic dial pulsing circuit/touch tone keypad

23. Basic telephone call procedures
Step 1: Calling station goes off hook
Step 2: Switching machine returns an audible dial tone to the calling station
Step 3: Caller dials the destination #
Step 4: Switching machine removes the dial tone from the loop
Step 5: Switch interprets the # and locates the local loop for the destination #

24. Basic telephone call procedures
Step 6: Switch check the destination for the DC current
If off hook, busy signal sends to the calling station
If on hook, ringing signal and ring back signal will be sent
Step 7: When destination answers the call, it completes the loop causing DC current to flow.

25. Basic telephone call procedures
Step 8: Removes the ringing and ring back signal
Step 9: When either end goes on hook
The switch machine detects an open circuit, then drops the connection through the switch

26. Call Progress Tones & Signals
Acknowledgement & status signals that ensure the processes necessary to set-up and terminate a telephone call are completed in an orderly & timely manner
Signaling
Station signaling –exchange of signaling message over local loops between stations & tel. company switching machines
Intraoffice signaling – exchange of signaling message bet. switching machines

27. Categories of Signaling
Alerting signals
Indicate request for service
Ex. Going off hook, ringing the destination
Supervising signals
Provide call status information
Ex. Busy, ring back signal
Controlling signals
Provide information in the form of announcement
Ex. Change of number, number no longer in service
Addressing signals
Provide routing information (calling & called numbers)

28. Essential Call Progress Signals
Dial tone
Dual tone multifrequency tones
Multifrequency tones
Dial pulses
Station busy – slow busy
Equipment busy - fast busy
Congestion tone
Ringing
Ring back
Receiver on hook
Receiver off hook

29. Essential Call Progress Signals
Dial tone
2 frequencies – 350 & 440Hz
Dual tone multifrequency tones (touch tones)
Introduced in 1963 with 10 buttons
Each digit is represented by the linear addition of two frequencies
Used to transfer digits & control signals between telephone sets & local switching machines

30. DTMF Keypad Frequencies
1209 Hz
1336 Hz
1477 Hz
1633 Hz
697 Hz 1 2
ABC 3
DEF A
770 Hz 4
GHI 5
JKL 6
MNO B
852 Hz 7
PRS 8
TUV 9
WXY C
941 Hz * # D

31. Essential Call Progress Signals
Multifrequency tones
Combination of two frequencies that fall within the same speech BW so that they can be propagated over the same circuits as voice (in-band signaling)
Used to transfer digits and control signals between switching machines
Transmit the calling & called numbers from originating tel. office to the dest. tel. office

32. Multifrequency Codes Frequencies (Hz) Digit or Command 700 + 900 1 2 3 4 5 6 7 8 9
Key pulse (KP)
Start (ST)
2600
IDLE

33. Multifrequency Rate of transmission – 7 digits per second
KP - Used to indicate the beginning of a sequence of MF digits
ST – used to indicate the end sequence of dialed digits
Indicates the beginning of the processing of the signal (telephone circuit perspective)

34. Dial Pulses Rotary dial pulsing
The process begins when the telephone set is lifted off hook
When a digit is dialed
The loop circuit alternately opens (breaks) & closes (makes) a prescribe number of times
Rate – 10 make/break cycle per second
100 ms per pulse cycle
Break time 61 ms, make time 39 ms
Interdigit time – 300 ms

35. DTMF Subscriber Min. digit duration 50 ms Min interdigit duration
Max interdigit duration
3 s

36. Essential Call Progress Signals
Station busy
Sent from the switching machine back to the calling station whenever the called tel # is off hook
2 tone signal, 480 Hz and 620 Hz,
0.5 s on/off
60 pulse-per-min
Equipment busy
Congestion tone or no circuit available tone
Blocking condition
0.2 s on, 0.3 s off
120 pulse-per-min

37. Essential Call Progress Signals
Ringing signal
20 Hz, 90 Vrms
‘on’ for 2 sec
‘off’ for 4 sec
Ring back
440 Hz & 480 Hz
Receiver on/off hook
On hook
used to terminate a call
Off-hook
Causes DC current (20-80mA)to flow on the loop
Request for service

38. Non-Essential Signaling & Call Progress Tones
Call waiting tones
Hold
Stutter dial tone (for voice mail)
Calling card service tone
Intrusion tones