1. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
מבנה רשת הטלפונים
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

2. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
מושגים בסיסיים
PSTN : Public Switched Telephone Network.
T1/E1 : Protocol Of Carrying Voice In Frames.
POTS : Plane Old Telephone Services.
PRI/BRI : Primary/Basic Rate Interface - ISDN.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

3. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
מושגים בסיסיים
Off Hook : When Telephone Handset is up.(open)
On Hook : When Telephone Handset is down.(closed)
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

4. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
PULSE DIALING
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

5. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
TONE DIALING
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

6. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
Tone Dialing
Tone dials operate by sending a combination of frequencies that are translate into digits by the central office switch.
It uses 3 x 4 matrix to transmit pairs of frequencies to a tone receiver in the switch.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

7. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
Tone Dialing
Each of 12 buttons generates a unique pair of frequencies that are detected and translated into the called number.
For instance : dialing a ‘1’ produces the combined tone of 697 Hertz and 1.2 khertz.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

8. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
Tone Dialing
The choice of the frequencies is international, designed to prevent the creation of harmonics or overtones that misinterpreted by detection circuitry.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

9. Voice Channel Bandwidth
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

10. TDM : Time Division Multiplexing
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

11. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
TDM
TDM is a scheme in which numerous signals are combined for transmission on a single communications line or channel.
Each signal is broken up into many segments, each having very short duration.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

12. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
TDM
The circuit that combines signals at the source end of a communications link is known as a multiplexer.
It accept the input from each individual end user, break each signal into segments, and assigns the segments to the composite signal in a rotating, repeating sequence.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

13. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
TDM
At the other end of the long-distance cable, the individual signals are separated out by means of a circuit called a demultiplexer, and routed to the proper end users.
T users using TDM.
E users using TDM.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

14. Digitizing Voice : PCM Waveform Encoding
Nyquist Theorem : sample at twice the highest frequency.
Vice frequency range: kh.
Sampling frequency at 8 kHz - every s.
each sample is 8 bit.
8000hz x 8 bit = 64 KBPS.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

15. PCM - Pulse Code Modulation
Designed to carry digitized voice, based on AT&T FDM hierarchy.
STEP 1 : Sample analog signal at 8 kHz.
Results: Pulse Amplification Modulation (PAM).
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

16. PCM - Pulse Code Modulation
STEP 2 : Digitize PAM samples to 13 bits and compress to 8 bits using A-law or -law.
Result : Pulse Code Modulation (PCM).
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

17. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
-Law and A -Law
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

18. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
-Law and A -Law
In North America: -Law
y=ln(1+ x)/ln(1+ ), =255
in Europe : A-Law
y=(1+ln Ax)/(1+ln A), A=87.6
Linear for small values of x and logarithmic for larger values.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

19. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
-Law and A -Law
For example :
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

20. Voice Compression Technologies
Objective : reduce bandwidth consumption.
Compression algorithms are optimized for voice.
Unlike data compression : these are “loose”.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

21. Differential PCM-DPCM
Based on the relatively slow changes between successive samples.
Fewer bits are required to describe the differential from one sample to the next, than to describe the absolute signal level.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

22. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
Adaptive DPCM-ADPCM
To improve the resolution, DPCM contains a predictor that “guesses” the next sample.
The encoder quantizes the difference between the new sample and the predicted new sample.
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

23. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN
NEXT LESSON
Voice compression(3 Algorithm)
CELP
CS-ACELP
LD-CELP
INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN