Telephony Networking

Lesson 1: Telephony Essentials

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)

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)

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

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

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

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

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

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)

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

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

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”

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

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

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

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

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

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)

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)

Lesson 2: Boundaries, Numbers, Wiring and Safety

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])

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

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

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

RJ-11 Connectors and Wiring

RJ-12 Modular Connector

BT-431A Connectors

BT-631A Connectors

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

Wall Jack Wiring Diagram

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

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

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

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

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

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

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])

Lesson 3: Troubleshooting

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)

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

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"

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

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

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

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

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

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

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

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)

Lesson 4: Analogue and Digital Signaling

Objectives Identify basic ISDN services and protocols, including time slots, channels, ISDN2e/Basic Rate Interface (BRI), ISDN30/Primary Rate Interface (PRI) 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) Define the Q.931, Q.932, I.430 and Q.921/High-level Data Link Control (HDLC) standards, including identifying the typical call progress signals (e.g., alerting, call proceeding, etc.)

Objectives (cont’d) Explain the purpose of network termination equipment (NTE), including timing, conversion of signaling types, troubleshooting interface Define QSIG, H.450 (including supplementary services), Digital Access Signaling System 1 (DASS1), private networking, and Digital Private Network Signaling System (DPNSS) Define Signaling System 7 (SS7)/Common Channel Signaling 7 (C7) functions, including call setup, management and teardown; signaling links; signaling points (e.g., service switching point [SSP], signal transfer point [STP], service control point [SCP])

Signaling Categories Signaling categories: Supervision – detects changes to a particular line Addressing – responsible for routing signals to the correct switch Alerting – audible alert signals Call progress – signals that maintain calls

In-Band and Out-of-Band Signaling In-band signaling The process of allowing the control signal to share the same path as the voice and data Out-of-band signaling The process of using a separate channel for signaling purposes

Loop-Start Analogue Trunk Signaling

Integrated Services Digital Network (ISDN) ISDN can carry voice, fax, imaging or data communications Two types of ISDN: Basic Rate Interface (BRI) – Two 64-Kbps channels for voice or data; one 16-Kbps channel for signaling Primary Rate Interface (PRI) – 32 64-Kbps channels for voice or data; two 16-Kbps channels for signaling B channel (bearer channel) – carries voice or data D channel (delta channel) – carries signaling

ISDN Protocols I.430 – explains how the ISDN interface uses the physical and data link layers of the OSI/RM (Layers 1 and 2, respectively) ISDN interfaces must use reference points between the telco and the end station: U interface S interface T interface Network termination equipment (NTE) Terminal adapter Terminal equipment

ISDN Protocols (cont'd) High-level Data Link Control – Link Access Protocol D channel (HDLC–LAPD) Used in ISDN connections to provide signaling LAPD also known as Q.921 LAPD operates solely in the D channel of an ISDN line LAPD provides flow control and data reliability Q.931 and Q.932 Q.931 manages how a session is begun and ended Q.932 makes it possible to modify connections that are already under way

Private Integrated Services Network (PISN) A private network providing services to a specific set of users (not to the general public) Formed when digital PBXs communicate with one another over private ISDN lines Communications can be private and encrypted A private numbering plan can be implemented A PINX is a piece of equipment (such as a PBX and/or other networking equipment, such as a router) used to create a PISN PINX provides automatic connection-handling functions

PISN Signaling Methods Digital Private Network Signaling Scheme (DPNSS) – a collection of protocols that enable PBX-to-PBX communication over ISDN lines Tromboning – a problem that occurs when a second connection is opened unnecessarily to accommodate a call that is being re-transferred back from one PINX to another QSIG – the de facto standard for PISNs connected by PINX equipment through ISDN lines QSIG basic services – enable PISN elements to establish voice and data calls QSIG supplementary services – help control remote PINXs built by different manufacturers Additional network features (ANF) – signaling enhancements that help handle calls

PISN Signaling Methods (cont'd) QSIG basic call (QSIG BC)

Q and C Reference Points Q reference point – the point at which a logical PINX interface communicates with a remote PINX C reference point – the physical interface between a PINX and a trunk line

Signaling System Seven (SS7) Signaling System Seven (SS7) – a packet-switched network protocol used by telcos in calls that pass between switches SS7 network and protocols are used for: Basic call setup, management and teardown Wireless services such as internetwork roaming Toll-free and toll services Local number portability Enhanced calling features High-level Data Link Control (HDLC) – a protocol that divides signaling data into discrete packets HDLC frame

Signaling System Seven (SS7) (cont'd) SS7 elements: Service Switching Point (SSP) Signaling Transfer Point (STP) Service Control Point (SCP) SS7 signaling links: Access (A) links – connect SSPs to STPs Bridge (B) links – connect STP pairs in the same level of the SS7 hierarchy Cross (C) links – connect each STP in a mated pair to its mate Diagonal (D) links – connect STP pairs on different levels of the SS7 hierarchy Extended (E) links – connect an SSP to an alternative STP pair Fully associated (F) links – connect mobile network SSPs directly to each other

Computer-Telephony Integration (CTI) CTI – the ability for telephony networks and data networks to share data

Summary Identify basic ISDN services and protocols, including time slots, channels, ISDN2e/Basic Rate Interface (BRI), ISDN30/Primary Rate Interface (PRI) 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) Define the Q.931, Q.932, I.430 and Q.921/High-level Data Link Control (HDLC) standards, including identifying the typical call progress signals (e.g., alerting, call proceeding, etc.)

Summary (cont’d) Explain the purpose of network termination equipment (NTE), including timing, conversion of signaling types, troubleshooting interface Define QSIG, H.450 (including supplementary services), Digital Access Signaling System 1 (DASS1), private networking, and Digital Private Network Signaling System (DPNSS) Define Signaling System 7 (SS7)/Common Channel Signaling 7 (C7) functions, including call setup, management and teardown; signaling links; signaling points (e.g., service switching point [SSP], signal transfer point [STP], service control point [SCP])

Telephony Networking Telephony Essentials Boundaries, Numbers, Wiring and Safety Troubleshooting Analogue and Digital Signaling