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Chapter 2

Chapter 2. Voice Communications Concepts and Technology. Objectives. Investigate PSTN Study and understand digital voice communication and digitization Understand PBXs Understand CTI and voice services Introduce Digital voice transmission services. GOAL. Study the business behind

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Chapter 2

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  1. Chapter 2 Voice Communications Concepts and Technology

  2. Objectives • Investigate PSTN • Study and understand digital voice communication and digitization • Understand PBXs • Understand CTI and voice services • Introduce Digital voice transmission services

  3. GOAL Study the business behind voice communication

  4. Basic Concepts • Voice consists of sound waves of varying frequency and amplitude. • The transmitter part of phone handset converts voice into electrical signals to be transmitted onto the analog network. • The receiver part of a handset works the opposite of the transmitter.

  5. Getting Voice Onto and Off the Network

  6. Basic Concepts • POTS (Plain Old Telephone Service) employs analog transmissions to deliver voice signals from source to destination. • The bandwidth is 4000 Hz, but guardbands limit the useable range to 300-3300 Hz. • Today, the local loop is still analog, but high-capacity digital circuits typically link the exchanges or Central Offices.

  7. Voice Bandwidth

  8. Voice Network Concepts • PSTN • Network hierarchy • Signaling and dial tone • Control and management:

  9. Figure 1-3 Basic Telecommunications Infrastructure

  10. Representative Voice Network Hierarchy

  11. Signaling and dial tone • Requested destinations are presented to the CO by dialing a series of numbers. • Numbers tell whether the call is local, intra-LATA, or inter-LATA. Subsequently, concerned circuits are solicited. • Numbers are generated: • Rotary phones: pulses • Dual-tone multi-frequency tones. • Tones are used to enable specialized services from PBX’s, carriers, banks, information services, and retail information.

  12. Tone Dialing with DTMF

  13. Voice Digitization • Principle: • To convert voice signal from analog to digital • The voice conversation must be sampled frequently enough so that the resulting conversations resembles the voice of the call initiator • Codec (coder/decoder): • device used to transform analog transmissions into a stream of binary digits.

  14. Voice Digitization • Pulse Amplitude Modulation: (PAM) • Varies the amplitude of the electrical pulses • Used in earlier PBX’s. • Pulse Duration Modulation: (PDM/PWM) • Varies the duration of electrical pulses • Pulse Position Modulation: (PPM) • Varies the duration between electrical pulses

  15. Voice Digitization: PAM PDM PPM

  16. Pulse Code Modulation • The most common method used to digitize voice is Pulse Code Modulation (PCM). • PCM uses: • 8000 samples/sec • 8 bits/sample • therefore, 1 digital voice channel requires 64 Kbps • known as a DS-0 circuit.

  17. Voice Digitization: Pulse Code Modulation (PCM)

  18. Adaptive Differential PCM (ADPCM) • Each voice channel uses 4 bits. • ADPCM supports 48 simultaneous conversations over aT1 circuit. • The standard for 32-Kbps is known G.721. • The G.721 is used as a quality reference point for voice transmissions (Toll Quality).

  19. ADPCM • ADPCM is used to send sound on fiber-optic long-distance lines as well as to store sound along with text, images, and code on a CD-ROM

  20. Voice Compression • ADPCM is also known as voice compression. • Advanced techniques employ DSP’s. • DSP’s are able to compress voice in as little as 4800 bps. • Efficiency: 13 times more than PCM. • Voice compression may be accomplished by stand alone units, or by integral modules within multiplexers.

  21. Private Branch Exchanges • A PBX is similar in function to a public exchange. • A PBX is exclusively used by the organization and physically located on the organization’s premises. • Provides an interface between users and the shared network (PSTN). • Additional services offered by a PBX allow users to use their phones more efficiently and effectively. • Medium to large organizations can save a lot of money by using a PBX

  22. Popular vendors of PBX equipment • Nortel, Lucent (25% of the market) • Siemens, Rolm • NEC, Mitel

  23. PBX Architecture • PBX overall functionality and added features are controlled by software programs. • Those programs are executed by specialized computers. • Programs reside in: CPU, stored program control or common control area. • User phones are connected to line cards. • Trunk cards allow connection of the PBX to outside world.

  24. PBX Physical Architecture

  25. PBX Technology Analysis • PBX features and services end to fall into three categories: • features and services: • that provide users with flexible usage of PBX resources. • that provide for data/ voice integration • that control and monitor the use of those PBX resources.

  26. Voice Based Features and Services • Common features: • Conference calling, Call forwarding, Call transfer, Speed dialing, Redialing, Call hold. • Least Cost Routing (Selecting lowest price LD provider). • Automatic Call distribution • Call pickup • Night Mode

  27. Data/Voice Integration Features and Services • Data is transmitted either: • through the PBX via a dedicated connection or • a hybrid voice/data phone is used to transmit both voice and data simultaneously over a single connection. • Features: • ISDN support, T-1 support, Data interfaces, PBX to host interfaces.

  28. Control and Monitoring Features and Services • Basic: (e.g.) • Limiting access to outside lines from certain extensions. • Advanced: • Call accounting system: program run on a separate PC directly connected to the PBX. • Process within the PBX known as station message detail recording (SMDR) where an individual detail record is generated for each call. • Used for spotting abuse and allocating phone usage on a departmental basis.

  29. Call Accounting Systems Installation

  30. Auxiliary Voice Related Services • Auxiliary add-on device that provides the following services: • Automated attendant • Voice mail • Voice response units (VRU): Interactive voice response (IVR). • Voice processor: e.g. speech recognition • Voice server: a LAN based server that stores, and delivers digitized voice messages. Used with voice mail system. • Music / ads on hold

  31. PBX Architecture Trends • PBX user demands: • Better connectivity between phones and desktop PCs. • Better connectivity between PBXs and LANs • More open PBX architecture for easier access to PBX features and services from a variety of computing platforms. • Better integration of PBX management programs with enterprise network management packages.

  32. Open PBX Architecture • Logical separation between the call processing functionality and the underlying switching fabric. • Allow to introduce newer and faster switching technology without redesigning entire PBX. • Support of industry standard API: TAPI and TSAPI for telephony applications. • New services can be designed and interfaced to a variety of PBXs and computers.

  33. Open PBX Architecture

  34. PBX Trends • Architectural Trends • Multi-vendor Interoperability standards: • International standard: Q.Sig (allows interoperability between PBX’s and ISDN). • PBX integration with wireless phones support: • Cordless Telephone generation 2 (CT2). • Common air Interface (CAI) global standard for low power wireless transmission. • Mini PBX’s for the Small Office Home Office Market (SOHO).

  35. Mini PBX’s for the Small Office Home Office Market • Mini PBX’s known as multifunction telephony boards or PC expansion boards: • Multiple workers share a small number of phone lines with features such as: • Auto attendant software • Integration with cell phones, pagers, and voice mail systems. • ISDN Support

  36. Computer Telephony Integration (C T I) • CTI attempts to integrate the phone and the computer to increase productivity. • Examples of the integration: • Call control: allows users to control their telephone functions through their computer. • Fax on demand: users can dial-in using a telephone and request fax documents.

  37. C T I • Unified messaging: • keeps voice-mail, e-mail, and faxes together in one place (universal in-box). • Audiotex: • Deliver audio information to users based on responses on the touch-tone keypad to prerecorded questions (hotline questions). • Interactive Voice Response (IVR): • Support online transaction processing. Used in banks to allow users to transfer funds between accounts.

  38. C T I Architecture1 - PBX to host interfaces • In PBX-to-host interface CTI was achieved by linking mainframes to PBXs via PBX-to-host-interface. • Applications were compatible with computer and PBX. • Systems linked to an automatic call distribution unit (ACD) • All phones are controlled by CTI application running on mainframe computer. • Expensive systems.

  39. C T I Architecture2 - Desktop C T I • First party call control • Less expensive alternative to PBX-host architecture. • PC’s are equipped with telephony boards and associated control software. • Each PC controls only the telephone to which it is attached. • No overall automatic call distribution across multiple agents and their phones. • No sharing of call related data among the desktop CTI PC’s.

  40. C T I Architecture3 - Client/Server C T I • CTI server computer interfaces to the PBX or ACD to provide overall system management. • Individual client based CTI applications execute on multiple client PCs. • Multiple CTI applications on multiple client PCs can share the information supplied by the single CTI Server. • Offers overall shared control of the PBX-to-host CTI architecture at a cost closer to that of the desktop architecture.

  41. CTI Architectures

  42. Figure 2-20 Technology Required to Develop and Implement CTI Applications

  43. Alternatives to PSTN • Voice over the Internet • using a sound card, microphone, and speakers • can call others using the same product • gateways are being established to allow Internet voice callers to reach regular telephone users as well.

  44. Voice over the Internet • Underlying transport protocols (IP and UDP) deliver voice conversation. • IP = internet protocol • UDP = User datagram protocol • IP and UDP can be used in any of the following: • Modem based point-to-point connections • Local area networks • Private Internets (Intranets)

  45. VOIP Transmission Technology and Topologies

  46. Alternatives to PSTN (cont’d) • Example of products: • CoolTalk • Internet Phone • Intel Internet Phone • Microsoft NetMeeting • Webtalk • TeleVox

  47. Voice over Frame relay • Variable-length delay introduced by variable-length frames is unacceptable for voice. • Frame relay access device (FRAD) accommodates both voice and data: • Voice prioritization: priority given to voice • Data frame size limitation: to limit delays • Separate voice and data queues.

  48. Voice over Frame relay • Voice conversations require 4 – 16 Kbps of bandwidth. • Permanent Virtual Circuit (PVC): maintained end to end connection throughout the voice conversation. • Voice conversation can take place between locations directly connected to a frame relay network. • No current standards defined between frame- relay networks and the voice based PSTN.

  49. Voice Transmission over a Frame Relay Network

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