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Chapter 5 Voice Communications.

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Presentation on theme: "Chapter 5 Voice Communications."— 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 Receiver Switchhook Dialing Ringing
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 Design considerations
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 Bandwidth 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 Frequency Phase Loudness Vibration speed
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, carrier’s 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
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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