Chapter 5 Voice Communications Agenda Telephone

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 • Dialing – Rotary dial – Dual-tone-multifrequency (DTMF) or touch tone • Ringing – Call setup time

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

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

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

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

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

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 - 4 k. Hz) Supergroup (5) master group (10) Jumbo group

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

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 (SS 7) – Use separate lines to set up telephone calls – Optimizing the digital networks – Offer enhanced services

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

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

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

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 (busy hour) 1 -5% (Blocking) grade service level

Internet Telephone Calls • • • Voice over IP (Vo. IP) Benefits Problems Impacts Future

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

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)

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

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

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

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

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

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

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)

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

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

Discussion • Design a voice communication system for an airline