telephony networking

TelephonyNetworking

Lesson 1:Telephony Essentials

Telephony Networking

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)

• 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



• 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



• 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


• 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



• Multimetre– Measures resistance, current and voltage in

an electrical circuit



• 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


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)


• 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 andOut-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

Router

E1 TrunkConnection to

Exchange32 DS0

channels

ISDN-PRITrunk

(30B+2D)to Exchange

E1 TrunkConnectionto Exchange

Non-channelized

Ground(6 feet)

Server

Database

Ethernet

Line Adapter Card

Line Adapter Card

Line Adapter Card

Line Adapter Card

Line Adapter Card

RJ-45 Line Adapter Card

OperatingSystem CPUAutomatic RouteSelection (ARS)

Least Cost Routing(LCR)

Trunk AdapterCard

Trunk AdapterCard

Trunk AdapterCard

PBX

Analog Phone

Analog Phone

Digital Phone

Digital Phone

Analog Modem


Summary

Identify basic ISDN services and protocols, including time slots, channels, ISDN2e/Basic Rate Interface (BRI), ISDN30/Primary Rate Interface (PRI)


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

telephony networking

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