Mode of Communication - Voice and Data
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This document summarizes key components and processes involved in basic telephone communication systems. It discusses the basic components of a telephone system including the subscriber loop, local exchange, telephone set, and transmission medium. It then describes the essential components of a standard telephone set and basic call procedures. Finally, it outlines common call progress tones and signals that facilitate telephone calls, such as dial tones, ringing, and busy signals.
Mode of Communication - Voice and Data
- 1. Prepared by: Nikhil Kumar Electronics & Communication Department 5th Semester NRI Institute of Research & Technology Bhopal
- 2. INTRODUCTION Communication • The process of conveying information from one place to another Components • Source of information • Transmitter • Receiver • Destination • Transmission medium
- 3. Telecommunication • A long distance communications • ‘tele’ Greek word for distant or afar Telephone • One of the most remarkable devices ever invented
- 4. 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)
- 5. Local Loop • Most fundamental component of a telephone circuit • Unshielded twisted pair(UTP) transmission line • Cable pair – 2 insulated conductors twisted together 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
- 6. Standard Telephone Set • Simple analog transceiver designed for converting speech of acoustical signals to electrical signals • Added features: multiple line selection, hold, caller ID Basic telephone set
- 7. 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
- 8. Essential Components Ringer Circuit • Electronic oscillator • 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)
- 9. Essential Components Equalizer circuit • 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
- 10. Essential Components •Transmitter •Converts acoustical signals in the form of sound pressure waves from the caller to electrical signals Microphone •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 Hybrid network •Enables the subscriber to output signals representing digits •Rotary dialer/Electronic dial pulsing circuit/touch tone keypad Dialing circuit
- 11. 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 #
- 12. Basic telephone call procedures • If off hook, busy signal sends to the calling station • If on hook, ringing signal and ring back signal will be sent Step 6: Switch check the destination for the DC current Step 7: When destination answers the call, it completes the loop causing DC current to flow. Step 8: Removes the ringing and ring back signal • The switch machine detects an open circuit, then drops the connection through the switch Step 9: When either end goes on hook
- 13. 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 • Interoffice signaling – exchange of signaling message bet. switching machines
- 14. 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)
- 15. 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 Essential Call Progress signals
- 17. DTMF Keypad Frequencies 700 + 900 1 700 + 1100 2 700 + 1300 3 700 + 1500 4 900 + 1100 5 900 + 1300 6 900 + 1500 7 1100 + 1300 8 1100 + 1500 9 1100 + 1700 Key pulse (KP) 1300 + 1500 0 1500 + 1700 Start (ST) 2600 IDLE