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

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

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

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

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

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

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

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

Voice Channel Bandwidth INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

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

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

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

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. T1 - 24 users using TDM. E1 - 30 users using TDM. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

Digitizing Voice : PCM Waveform Encoding Nyquist Theorem : sample at twice the highest frequency. Vice frequency range: 0.3-3.4kh. Sampling frequency at 8 kHz - every 125 s. each sample is 8 bit. 8000hz x 8 bit = 64 KBPS. INTRODUCTION TO TELEPHONY BY : ITZIK CHOEN

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

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

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

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

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

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

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

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

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