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Modern Telephony Systems: A Comprehensive Guide

Explore the evolution of telephony systems, from POTS to PBX, covering voice transmission, digitization, signaling, equipment, services, numbering, and more. Learn about modern trends and technologies shaping the future of telecommunications.

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Modern Telephony Systems: A Comprehensive Guide

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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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