Telephony Networking

1. TelephonyNetworking

2. Lesson 1:Telephony Essentials

3. Objectives • Define codec, and describe the G.711 protocol • Define Pulse Code Modulation (PCM), and distinguish between the μ-Law and A-Law companding algorithms • Explain common feature sets for voice calls, including call waiting, call blocking, call forwarding, call monitoring, callback, and additional private network features • Explain Direct Inward Dialing (DID) • Define hunt groups • Identify elements of a call centre or contact centre, including call routing, caller ID, automatic call distributors, pop-ups, instant messaging/chat, e-mail, real-time voice and data recording/storage, hosted solutions, and elements of Computer Telephony Integration (CTI)

4. Objectives (cont’d) • Explain the purpose of network termination equipment (NTE), including timing, conversion of signaling types, troubleshooting interface • Identify symptoms of improper clocking configuration (e.g., problems with synchronization) • Resolve problems when connecting time division multiplexing (TDM) networks (e.g., in-band and out-of-band signaling, digital and analogue setup messages, safety practises and standards, crosstalk, split, line imbalance, open, short, earthing issues, echo cancellation in two-wire-to-four-wire hybrids)

5. Analogue to Digital Pulse Code Modulation (PCM) – converts analogue voice data to digital format, then back to analogue • PCM uses two compression algorithms: • Mu-Law (used only in North America and Japan) • A-Law (the standard for all international circuits) • G.711 – international standard for encoding voice on a 64-Kbps channel

6. Exchange Connections • Point of presence (POP) – an interexchange carrier that connects long-distance services to a local connection • Private Branch Exchange (PBX) – enables an organisation to create an internal telephone-numbering system • Direct Inward Dialing (DID) / Direct Dialing Inward (DDI) – enables multiple telephone numbers to be used on a few lines

7. Common Voice Call Features • Call waiting– suspends current call to pick up another incoming call • Call blocking– prevents calls from ringing through based on point of origination; also, restricting a station from making outbound or long-distance calls • Call forwarding– redirects calls from one phone number to a second phone number • Callback– monitors a busy phone and completes a call to that number when the busy phone goes back on-hook

8. Additional Private Features • Call monitoring– keeps detailed records of phone transactions • Traffic reporting– reports that detail usage on incoming and outgoing trunk groups • Ringing preferences– programs certain lines to ring only on particular stations • Automated attendant– answers call, collects station number of desired party, then transfers the call • Voice mail systems– integrated voice mail • Outward restrictions– restricts stations to making only intercom or local calls • Private numbering plans– allow users to call internal extensions without using an outside line • Unified messaging– stores all forms of messaging, e-mail, voice mail and fax, in a centralized server

9. Hunt Groups • Allow incoming calls to be routed to available alternate numbers • Most-idle line hunting– used to distribute the load over all trunks • Sequential hunting– hunts in a sequence from the dialed number through to the end of the hunt group • Circular hunting– hunts all lines in the hunt group before returning a busy signal

10. Call / Contact Centres • Centralized office used for processing a large volume of calls • Companies use call centres to interact with their customers • Calls are automatically distributed among agents • Predictive dialers automatically dial batches of phone numbers for connection to agents • Calls are recorded for quality assurance and legal purposes • Contact centres allow for interaction with agents via phone, e-mail, chat or instant messaging, and Web (click-to-talk)

11. Call / Contact Centre Software • Automatic call distribution (ACD)– used to distribute the load over all trunks • Interactive voice response (IVR)– allows a caller to interact with a database • Customer relationship management (CRM)– integrates with ACD software, allowing the software to query the database and display customer information on an agent’s screen • Metrics– enable supervisors to analyze performance

12. Elements of Computer-Telephony Integration (CTI) • Calling line information display • Authentication of callers • Interactive voice response to callers • Live voice or touchtone input • On-screen pop-ups • On-screen dialing and phone control • Receiving and routing fax messages • Logging on • Agent instruction • State control • Multi-channel blending • Managing voice or video conferences • Call routing and reporting

13. Hosted Solution Benefits • Relatively short and simple start-up cycles • Eliminates the need for specialized staff • Tech support and maintenance handled by hosting company • Allows for maximum flexibility in agent placement and routing of incoming calls to agents • Enables a “virtual call centre”

14. Trunks and Signaling • Analogue loop-start trunks used in most standard home phones • Earth-start trunk lines often used to connect a PBX to an exchange

15. The Primary Reference Source • Primary reference source (PRS) – a hierarchical system wherein a super-accurate time source is defined as stratum-0; used to time and synchronize digital connections • PRS strata • Stratum 1 – extremely accurate; usually provided by a GPS-enabled device • Stratum 2 – at one time used by long-distance providers, but now largely out of use • Stratum 3/3E – used by public exchanges, gatekeepers and gateways • Stratum 4 – used by PBXs and telco channel banks

16. PRS (cont’d) • Timing types • Asynchronous – no timing information is shared • Synchronous – a common system clock is used for all trunk lines and networks involved • Plesiosynchronous – a number of PRS clocks are used for all networks involved • Symptoms of improper clocking • Audible pops and clicks • Loss of data

17. Cabling and Wiring • Service wire centre – houses one or more local switching systems • Main distribution frame (MDF) – the main interface between the telco's lines and all internal lines • Patch panel – interconnects voice and data lines with RJ-11 and/or RJ-45 connectors

18. Call-Processing Steps • Placing a call • Call setup – the connection is built between the local loop and the exchange • Call connection maintenance – the connection is established and maintained • Call completion – breaking the connection • Common analogue transmission impairments • Loss – parts of the transmission are dropped • Echo – parts of the conversation are repeated • Noise – unwanted energy that interferes with the signal • Crosstalk – parts of another conversation are heard • Echo cancellation in hybrid networks • When two-wire and four-wire networks are connected, a hybrid network is created, which can result in echo • An echo canceller balances the ohm levels between the lines, thereby eliminating the echo

19. Summary • Define codec, and describe the G.711 protocol • Define Pulse Code Modulation (PCM), and distinguish between the μ-Law and A-Law companding algorithms • Explain common feature sets for voice calls, including call waiting, call blocking, call forwarding, call monitoring, callback, and additional private network features • Explain Direct Inward Dialing (DID) • Define hunt groups • Identify elements of a call centre or contact centre, including call routing, caller ID, automatic call distributors, pop-ups, instant messaging/chat, e-mail, real-time voice and data recording/storage, hosted solutions, and elements of Computer Telephony Integration (CTI)

20. Summary (cont’d) • Explain the purpose of network termination equipment (NTE), including timing, conversion of signaling types, troubleshooting interface • Identify symptoms of improper clocking configuration (e.g., problems with synchronization) • Resolve problems when connecting time division multiplexing (TDM) networks (e.g., in-band and out-of-band signaling, digital and analogue setup messages, safety practises and standards, crosstalk, split, line imbalance, open, short, earthing issues, echo cancellation in two-wire-to-four-wire hybrids)

21. Lesson 2:Boundaries, Numbers, Wiring and Safety

22. Objectives • Identify and use appropriate troubleshooting tools (e.g., four-pair tester, tone-and-probe kit, analogue and/or digital butt set, volt metre, time domain reflectometre) • Identify safety procedures for working with convergent network equipment (e.g., power, proper earthing, electrostatic discharge [ESD], radio frequency interference [RFI], electromagnetic interference [EMI])

23. Network Termination and Test Point (NTTP) • Network termination and test point (NTTP) • The point at which the telco’s network ends and connects with the wiring of the customer premises • Operational control or ownership of services changes here • Minimum point of entry (MPOE) – the point where telco equipment ends and inside local-loop wiring begins

24. Telephone Numbers • Global numbering plans • ITU Recommendation E.164 establishes standards for numbering plans • Telephone numbers should not exceed 15 characters • National numbering plans • Define the numbering structure for a specific country or group of countries • Regional numbering plans • Define the numbering structure for a specific geographic region • Private numbering plans • Allow companies to create their own numbering systems

25. Signaling Types • Three types of signaling: • Rotary / pulse or multifrequency (MF) – used on rotary dial phones • Dual-Tone Multifrequency (DTMF) – generated by touch-tone pads on all standard phones • Digital – does not process audible tones

26. RJ-11 Connectors and Wiring

27. RJ-12 Modular Connector

28. BT-431A Connectors

29. BT-631A Connectors

30. Line Jack Units • Three types of line jack units: • Master • PBX master • Secondary • Master line jack units contain: • A 26-amp surge protector • A 1.8 uf, 250-volt capacitor • A 470-ohm service resistor • Six terminals designed to accept wiring from the wall

31. Wall Jack Wiring Diagram

32. Common Telephony Issues • Quality assurance and business continuity • Uptime – the length of time a device has remained operational • Mean time between failure (MTBF) – the predicted amount of time a device will function before it requires maintenance or replacement • Mean time to repair (MTTR) – the time it will take to discover the failure and repair or restore service • Availability – the length of time a device or system is able to provide service • Availability = MTBF / MTBF + MTTR • Return on investment (ROI) – the calculations made to ensure that equipment will result in company profitability

33. Common Telephony Issues (cont’d) Telecommunications reliability issues: • Extreme temperatures • Lightning • Power requirements and heat • Electrical safety • Vibration and shock • Earthquake • Humidity • Contaminants • Fire • EMI immunity • Noise • Altitude

34. Common Telephony Issues (cont’d) • Electromagnetic compatibility • Electrostatic discharge (ESD) – An uncontrolled buildup of electrical current • Radio frequency interference (RFI) – A signal that causes another device to operate improperly • Electromagnetic interference (EMI) – interference produced by electromechanical devices • Solutions for electrical issues: • EMI suppression filters • Capacitors • Inductors • Shielding • Ensuring proper humidity

35. Common Telephony Issues (cont’d) • Personnel safety concerns and procedures • Tools • Loose clothing • Metal • Safety glasses • EMI, ESD and tools • Never work alone • Dust • Other problems

36. Testing Laboratories • Testing laboratory rooms and equipment • Fire, heat, humidity and moisture • Airborne contaminant • Electromagnetic • Shakers • Wind and rain • Pressure • Sound

37. Securing Equipment • Physically secure telephony equipment using brackets • Isolate power sources by earthing them properly • Earthing ring • Earthing lugs • Steel rod placed roughly 2 metres in the earth

38. Summary • Identify and use appropriate troubleshooting tools (e.g., four-pair tester, tone-and-probe kit, analogue and/or digital butt set, volt metre, time domain reflectometre) • Identify safety procedures for working with convergent network equipment (e.g., power, proper earthing, electrostatic discharge [ESD], radio frequency interference [RFI], electromagnetic interference [EMI])

39. Lesson 3:Troubleshooting

40. Objectives • Resolve problems when connecting time division multiplexing (TDM) networks (e.g., in-band and out-of-band signaling, digital and analogue setup messages, safety practises and standards, crosstalk, split, line imbalance, open, short, earthing issues, echo cancellation in two-wire-to-four-wire hybrids) • Identify and use appropriate troubleshooting tools (e.g., four-pair tester, tone-and-probe kit, analogue and/or digital butt set, volt metre, time domain reflectometre) • Identify symptoms of improper clocking configuration (e.g., problems with synchronization)

41. Short (continuity) Open (open fault) Terminator Cross Polarity Split Line imbalance Crosstalk Loopback testing End-to-end testing Troubleshooting Terms

42. Troubleshooting Tools • Telephone line-test set • Also called a butt set or handset • Used to test line quality • Used to check line polarity • Used to determine loss of current • End-to-end and loopback testing • A butt set is used to generate tones and frequencies to test lines • Can use analogue butt set to listen to digital communications by going into "data safe mode"

43. Troubleshooting Tools (cont'd) • Tone-and-probe kit • A tone generator emits tones across a wire • A probe listens on the other end of the wire for tones emitted by the tone generator • Uses • Identify open circuits • Locate short circuits • Identify breaks in a cable • Test polarity of a line • Determine line voltage • Identify lines that are causing crosstalk • Find a single conducting wire in a bundle of wires • Provide talk battery power to test a line with no dial tone

44. Troubleshooting Tools (cont'd) • Multimetre • Measures resistance, current and voltage in an electrical circuit

45. Troubleshooting Tools (cont'd) • Punchdown tool • Inserts wires in 66 and 110 punchdown blocks • Line tester • Determines whether a short exists in a line • DTMF decoder • Can capture, convert and play back DTMF signals • Modular breakout adapter • Breaks out all wires in a BT-431A, RJ-11 or RJ-45 jack into individual, easily accessible wires

46. Troubleshooting Analogue Lines • PBX and earth-start analogue lines • At the PBX, use a butt set to isolate crosstalk to determine whether the problem is within or outside the building • Securing connections with a punchdown tool • Poorly closed connections or improperly set lines can cause line noise • Checking for line noise • Use a digital multimetre to measure for AC voltage • AC voltage > 1 volt = improper earthing

47. Troubleshooting Digital Lines • Improper clocking configuration • Voice and data lines must be precisely synchronized using the exchange’s PRS • Use a butt set to check for improper clocking • Crossed signaling methods • Lines that use in-band signaling should not be directly connected to lines that use out-of-band signaling • Failed transmissions or garbled data can result • Check for proper termination • Be aware of different ISDN voice-encoding standards

48. Troubleshooting Digital Lines (cont'd) • Consider signal-to-noise ratio • Test equipment for digital networks • Signal/spectrum analyzer • Multimetre • Oscilloscope • Time domain reflectometre (TDR) • Service-specific test set

49. Troubleshooting Digital Lines (cont'd) • Telephones and ring voltage • REN value determines the ringing voltage • -90 v AC charge needed to ring a standard analogue telephone • Telco will not guarantee a phone to ring if a line has to service a number of devices that together constitute more than 4 REN in the UK (5 REN in North America) • Safety • Ensure that power is connected properly at the electrical termination device. • Use a residual current device (RCD) to guard against electrical shocks

50. Summary • Resolve problems when connecting time division multiplexing (TDM) networks (e.g., in-band and out-of-band signaling, digital and analogue setup messages, safety practises and standards, crosstalk, split, line imbalance, open, short, earthing issues, echo cancellation in two-wire-to-four-wire hybrids) • Identify and use appropriate troubleshooting tools (e.g., four-pair tester, tone-and-probe kit, analogue and/or digital butt set, volt metre, time domain reflectometre) • Identify symptoms of improper clocking configuration (e.g., problems with synchronization)