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Chapter 4 Voice Communications

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. Public Switched Telephone Network. Central office Lines

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Chapter 4 Voice Communications

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  1. Chapter 4Voice 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 • 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 • 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 • 7 5 6 4 3 2 1 0 • 128 64 32 16 8 4 2 1 • 0 0 0 0 0 1 0 0 • Transmit coded digital pulses representing measured amplitude (00000100)

  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 CriteriaBetween 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, e-mail, faxes and paper messages

  28. CTI LAN-based Application Standards & Tools • Standards • 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 • 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

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