1. Chapter 4 Voice Communications
Public Switched Telephone Network or Plain Old Telephone Service (POTS)
Private Telephone Systems
Computer Telephone Integration
Wireless Communication
Voice Transmission alternatives

2. Public Switched Telephone Network
Central office
Lines
Voice digitization
Numbering
Services

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 Equipment Functions Manual switching
Electromechanical switching
Electronic switching
Reliable
One total failure in 40 years
Quite & efficient
Less Labor costs with higher skill levels
Functions
AT & T dynamic non hierarchical routing (DNHR)
direct, redundancy, and alternate routing
Maximum 4 toll office

5. Central Office Hierarchy
Class 5: local central office
Tandem office
Class 4: toll center
Class 3: primary center
Class 2: sectional center
Class 1 regional center

6. Inter Office Signaling
Special network between central offices to set up telephone calls
Common channel interoffice signaling system (CCIS) by CCITT
Signaling system No.7 (SS7) By CCITT
Advanced intelligent network (AIN)
Software-defined network (SDN)
Calling number identification

7. Lines 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

8. Voice Digitization
Analog signals to digital signals (8000 samples/ sec)
Equipment
coder/decoder or codec (signal conversion)
Channel (signal conversion & loading into T-1)
Methods
Pulse amplitude modulation (PAM)
Pulse duration modulation (PDM) or pulse width modulaiton (PWM)
Pulse position modulation (PPM)
Pulse code modulation (PCM): most used with 256 possible amplitudes (2 to 8)
Adaptive differential pulse code modulation (ADPCM)

9. Pulse Code Modulation Sample amplitude of analog signal (4)
Present measured amplitude in binary notation
Transmit coded digital pulses representing measured amplitude ( )

10. Voice Digitization Bandwidth
DS-0 with 64,000 bits/sec
T-1 with 24 Ds-0
Adaptive differential pulse code modulation (ADPCM)
Need half of bandwidth for PCM
Used for voice compression with less quality

11. Telephone Numbering 9 geographic zones in the entire world Composition
Access code, carrier’s code,
Zone and country code
Area/city code
Exchange code
Subscriber code

12. Telephone Services - I Types of calls Local calling
Long distance calls
International calls
Operator services

13. Telephone Services - II
Calling card calls
Discounted calls
800 or 888 service
Geographic: interstate, intrastate, international (Universal International Freephone Numbering -UIFN)
Call direction: in, out, or both
900 service

14. 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

15. Private Telephone Systems
Key systems: 3 to 50 telephones
Private branch exchange (PBX) / private automatic branch exchange (PABX) / computer branch exchange (CBX): 50 to 10,000 or more
Centrex

16. PBX System Feature Automatic Call Distribution (ACD)
Data communication
Direct inward dialing (DID)
Hunt group (alternative trunks)
Least cost routing
Paging
Pick-up group
Prioritization
Night mode
Station message detail recording/call detail recording (SMDR)/(CDR)
Voice messaging

17. PBX Station Feature Automatic redial Automatic reminder Call forward
Call transfer
Call waiting
Camp on (call back)
Conference calls
Distinctive ringing
Do not disturb
Speed dialing

18. PBX Data/Voice Integration
ISDN support
T-1 support
Data Interfaces
PBX-to-host interfaces

19. PBX Auxiliary Service Automated attendant Voice mail
Voice response units (VRUs) or interactive voice response
Voice processor same as VRU
Voice server
Music/ads on hold

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. PBX Trends Multivendor interoperability standards
PBX integration with wireless phones
Mini-PBXs for home and small business

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

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

25. Computer Telephone Integration (CTI)
Architectures
Functions
Application standard

26. CTI Architectures PBX-to-host interfaces Desktop to CTI
Client/server CTI

27. CTI Functions Call control (on- line directory, conference calls)
Automated attendant
Automated call distribution
Audiotex
Fax-on-demand
Interactive voice response (IVR)
Outbound dialing
Unified messaging or universal in-box for voice mail, , faxes and paper messages

28. CTI LAN-based Application Standards & Tools
TSAPI (telephony services application program interface) by AT&T and Novell
TAPI (telephony application program interface) by Intel and Microsoft
Development tools
Visual Basic or Visual C++
Graphical code generator, debugging tool, interfaces to other applications (fax, sound)

29. Wireless Communication - I
Cordless telephone
Cellular telephone service
Transmitting voice & data
Security
Eavesdropping
Spread spectrum
Accident

30. Wireless Communication - II
Personal communication service
personal communication network (PCN) / personal handyphone system (PHS) / personal communication service (PCS)
Communication levels
Macrocells - car
Microcells -walking
Picells - building
Marine and aeronautical telephone services
Radio communication

31. Voice Transmission Alternatives
Internet - IP
Frame relay
Asynchronous transfer mode
Others

32. Internet Telephone Calls
Facilities
Hardware
Software
Benefits
Problems
Impacts (industry & regulation)
Future

33. Frame Relay Problems Frame relay access device (FRAD)
Variable-length frames
Delay
Frame relay access device (FRAD)
Voice prioritization
Data frame size limitation
Separate voice and data queues

34. Asynchronous Transfer Mode
Fixed-length frames (53 bytes cells)
Constant bit rate (not efficient)
Optimal methods
Voice compression
Silence compression
Variable bit rate (max: peak voice bit rate, min: guaranteed voice bit rate)

35. Others Voice/data multiplexers via T-1 Voice/data modem
Analog simultaneous voice and data: use switches
Digital simultaneous voice and data: digitize voice using analog line
ISDN BRI (basic rate interface) with two 64-kbps channels

36. Assignment
Review chapters 1-4
Read chapter 5
Prepare exam 1