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