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Chapter 5 Voice Communications. Agenda Telephone Central office Public Switched Telephone Network –Lines –Signals –Numbering –Services Private telephone.

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Presentation on theme: "Chapter 5 Voice Communications. Agenda Telephone Central office Public Switched Telephone Network –Lines –Signals –Numbering –Services Private telephone."— Presentation transcript:

1 Chapter 5 Voice Communications

2 Agenda Telephone Central office Public Switched Telephone Network –Lines –Signals –Numbering –Services Private telephone system Wireless communication

3 Telephone Set Transmitter –Analog signal Receiver –Sidetone Switchhook –On-hook and off-hook Dialing –Rotary dial –Dual-tone-multifrequency (DTMF) or touch tone Ringing –Call setup time

4 Central Office - I Switching equipment –Manual switching –Electromechanical switching Step-by-step switches Crossbar switches –Electronic switching Reliable One total failure in 40 years Quite & efficient Less Labor costs with higher skill levels Design considerations –Forecasting demand (time, duration, distance, culture) –Grade of service or blocking

5 Central Office - II End office or serving central office Toll office or switching office Central hub

6 Public Switched Telephone Network Line types –Local loop (pair of copper wires: tip and ring) –Drop wire –Distribution cable –Feeder cable –Trunk Copper wire Coaxial cable Microwave radio Fiber optic cable Internet line usage problem

7 Analog Signals - I Signal frequency –Sine wave –Cycle –Hertz (Hz): frequency per second Kilohertz (kHz) Megahertz (MHz) Gigahertz (gHz) Bandwidth –0 to 4,000 Hz (between 300 and 3,000 Hz) –Guard channel or guard band (buffer)

8 Analog Signals - II Amplitude –Loudness Frequency –Vibration speed Phase –Relative position of wave measured in degree

9 Analog Signals - III Modulation & demodulation (voice &carrier wave Three methods Amplitude modulation (AM) Frequency modulation (FM) Phase modulation (PM) Multiplexers –Base group, channel group or just group (12 - 4kHz) –Supergroup (5) –master group (10) –Jumbo group

10 Time Assignment Speech Interpolation (TASI) Pack multiple voice conversations onto a single telephone line Eliminate 10% of quite time in conversation

11 Inter Office Signaling Direct current (DC) signals –Dial tone signal Tone signals –Ringing, busy, and congestion signals Common channel signals –Common channel interoffice signaling system (CCIS) by ITU-T –Signaling system No.7 (SS7) –Use separate lines to set up telephone calls –Optimizing the digital networks –Offer enhanced services

12 Telephone Numbering 9 geographic zones by ITU-T Composition –Access code, carriers code, –Zone and country code –Area/city code –Exchange code –Subscriber code

13 Telephone Services - I Types of calls –Local calling –Long distance calls –International calls –Operator services

14 Telephone Services - II Calling card calls Discounted calls 800 service –Geographic: interstate, intrastate, international (Universal International Freephone Numbering -UIFN) –Call direction: in, out, or both 900 service

15 Telephone Services - III Software defined network (SDN) Foreign exchange (FX) lines Integrated Services Digital Network (ISDN) Selection criteria for telephone service –Time –Duration –Number –Location Usage pattern –Usage pattern (busy hour) –1-5% (Blocking) grade service level

16 Internet Telephone Calls Voice over IP (VoIP) Benefits Problems Impacts Future

17 Private Telephone Systems Key systems: 3 to 50 telephones Private branch exchange (PBX) / private automatic branch exchange (PABX) / computer branch exchange (CBX): over 50 Tie line or tie trunk for lease line Centrex Communication server

18 PBX System Features Data communication Direct inward dialing (DID) Hunt group Least cost routing Pickup group Station message detail recording/call detail recording (SMDR)/(CDR)

19 PBX Station Features Automatic reminder Call forward Call transfer Call waiting Camp on (call back) Distinctive ringing Do not disturb Speed dialing

20 PBX Security Block remote access Change access code and password Block outgoing calls during off-hours

21 Selection Criteria of PBX Maintenance Training Other support Price System feature Station feature Security feature

22 Centrex Service Regulated by public utilities commission PBX equipment in central office

23 Selection Criteria Between PBX and Centrex Regulation Maintenance Reliability Growth Control Capital investment

24 Audio Teleconferencing & Voice Mail Audio Teleconferencing Voice mail –Automated attendant –Audiotex –Interactive voice response

25 Wireless Communication - I Cordless telephone Cellular telephone service –Transmitting voice & data –Security Eavesdropping Spread spectrum Accident –Second generation systems Time division multiple access (TDMA) Global system for mobile communication (GSM) Code division multiple access (CDMA)

26 Wireless Communication - II Cellular telephone service –Third generation systems Japan: I-mode European: Wireless application protocol (WAP) Bluetooth: 33-foot radius Marine and aeronautical telephone services –Radio communication

27 Points to Remember Telephone Central office Public Switched Telephone Network –Lines –Signals –Numbering –Services Private telephone system Wireless communication

28 Discussion Design a voice communication system for an airline


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