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Chapter 5

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Chapter 5. Voice Communications. Agenda. Telephone Central office Public Switched Telephone Network Lines Signals Numbering Services Private telephone system Wireless communication. Telephone Set. Transmitter Analog signal Receiver Sidetone Switchhook On-hook and off-hook

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Chapter 5

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  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, 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 CriteriaBetween 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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