Chapter 5 Voice Communications

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

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

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

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 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)

Analog Signals - II Amplitude Frequency Phase Loudness Vibration speed 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 - 4kHz) 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 (SS7) 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 Usage pattern (busy hour) 1-5% (Blocking) grade service level

Internet Telephone Calls Voice over IP (VoIP) 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 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