telephony networking

Copyright © 2006 Prosoft Learning, a VCampus Company - All rights reserved.

TelephonyNetworking


Lesson 1:Telephony Essentials

Objectives

• Describe the basic components of the telephone service• Describe industry standards and protocols• Identify the purpose and function of the central office• Identify ways to connect to the central office• Identify various types of trunks and signaling methods• Explain various digital signal hierarchy terms and issues• Discuss SONET and SDH• Describe the purpose of the primary reference source• Describe the functions and uses of various types of

telephone cable and wiring plans• List the common call-processing steps

Telephony Basics

• Basic telephone service consists of:– Public switched telephone network (PSTN) – a

system of interconnected lines and switches– Plain old telephone service (POTS) – standard

telephony wires that carry analog data• The last mile – the POTS portion of the PSTN that

connects to a home or business (usually 2.5 miles)• The local loop – the tip and ring wire in the RJ-11

connector that provide a complete circuit to the central office

• On-hook condition – the line is not busy and is ready for a connection

• Off-hook condition – the line is busy

Telephony Basics (cont'd)

• Phone company terminology:– Local exchange carrier (LEC) – the local

telecommunications company– Local access and transport area (LATA) – the

area serviced by a LEC– Incumbent local exchange carrier (ILEC) – a

telco already in business before the Telecommunications Act of 1996

– Competitive local exchange carrier (CLEC) – a company that competes with LECs and ILECs

– Interexchange carrier (IXC) – a company that carries long-distance calls between LECs in different LATAs

Industry Standards and Protocols

• International Telecommunications Union (ITU) – manages worldwide telephony and networking standards– ITU-T series – standards documents labeled

A through Z– Radio Equipment and Telecommunications

Terminal Equipment directive – determines standards for wireless devices in the United Kingdom and Europe

• Internet Engineering Task Force (IETF) – publishes Requests for Comments (RFCs) that provide information about standardized Internet protocols

The Central Office

• Central office (CO) – switching location for local and long-distance calls

• CO uses three types of switches:– Class 3 (also known as an IXC, remote or long-

distance switch)– Class 4 (also known as a tandem switch)– Class 5 (also known as an end-office switch)

• Pulse Code Modulation (PCM) – converts analog voice data to digital format, then back to analog

• PCM uses two compression algorithms:– Mu-Law (used only in North America and Japan)– A-Law (the standard for all international circuits)

CO Connections• Point of presence (POP) – an interexchange carrier

that connects long-distance services to a local connection

• Foreign Exchange Service (FX) – provides telephone services from a CO that is outside the local calling area

• Private Branch Exchange (PBX) – enables an organization to create in internal telephone-numbering system

• Centrex – enables an organization to provide a pool of lines (alternative to PBX)

• Direct Inward Dialing (DID)/Direct Dialing Inward (DDI) – enables multiple telephone numbers to be used on a few lines

Trunks and Signaling

• Trunk – a direct communication line between two switching systems; used to establish end-to-end communications between customers – Ear and mouth (E&M) trunks – carry voice and data on

one series of lines, and signaling on a separate set of lines

– Analog loop-start trunks – use two wires (the tip and the ring) to act as conductors for the connection

– Ground-start trunk lines – require that both ends of a connection detect ground before the tip and ring wires can create a loop

– Digital trunk lines – signaling information and data are sent digitally

• A and B bits – signaling bits that allow a line to determine when connected systems check for dial tone and whether a remote system is in an on-hook or off-hook condition

Digital Trunks and the Digital Signal Hierarchy

• Digital signal hierarchy (DSH) – provides a standard for digital signal levels

• Use DSH to purchase the required amount of network bandwidth to accommodate telephone and network connections

• DSH levels are analogous to the T-carrier system • Digital signals use frames to carry data and

addressing information:– Super frame– Extended super frame (the most common

standard)

SONET and SDH

• Synchronous Optical Network (SONET)– High-speed, fiber optic networks organized in rings

• Synchronous Digital Hierarchy (SDH)– Fiber ring networks used internationally– Essentially the same as SONET

SONET and SDH (cont'd)

The basic measure of SONET speed is the Synchronous Transport Signal level 1 (STS-1) frame, which travels at 51.84 Mbps


The basic unit for SDH is the Synchronous Transport Module (STM)-1 frame, which travels at 155.52 Mbps


Benefits of using SONET/SDH• You can use multiplexors and routers to combine

different data lines and streams onto one line • One heterogeneous network can communicate with

another distant heterogeneous network via one fiber optic ring

The Primary Reference Source

• Primary reference source (PRS) – a network of hyper-accurate clocks used to precisely time digital connections

• PRS strata– Stratum 1 – extremely accurate but very expensive– Stratum 2 – used by long-distance providers– Stratum 3 – used by the CO– Stratum 4 – used by PBXs

• 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

Cabling and Wiring

• Service wire center – 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

• Intermediate distribution frame (IDF) – connects the MDF and a user's telephone handset

• Combined distribution frame (CDF) – same as MDF and IDF but also houses connections from incoming lines and lines from inside equipment

• Minimum point of entry (MPOE) – the point at which phone lines first enter your facility– Network interface device (NID) – terminates the connections

from the central office– Load coil – device that improves voice transmission– Bridge tap – cable used to extend the loop

Call-Processing Steps

• Placing a call– Call setup – the connection is built between the local loop

and the CO– Call connection maintenance – the connection is

established and maintained– Call completion – breaking the connection

• Common analog 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

Describe the basic components of the telephone service Describe industry standards and protocols Identify the purpose and function of the central office Identify ways to connect to the central office Identify various types of trunks and signaling methods Explain various digital signal hierarchy terms and issues Discuss SONET and SDH Describe the purpose of the primary reference source Describe the functions and uses of various types of

telephone cable and wiring plans List the common call-processing steps


Lesson 2:Investigating the Local Loop

Objectives

• Explain the importance of a demarcation point in telephony

• Identify signaling types used in the local loop• Use numbering standards, including the North

American Numbering Plan (NANP) and United Kingdom standards

• Explain how the local loop is wired• Wire RJ-11 and RJ-12 connectors• Wire BT-431A and BT-631A connectors • Wire a wall jack and a line jack unit

Inside the Demarcation Point

• Minimum point of entry (MPOE)– The telco's demarcation point– The point where telco equipment ends and

inside local loop wiring begins• Drop wire – the line from the telephone pole to the

MPOE• Station wire – the line inside the MPOE

Getting to the Local Loop

• Global numbering plans– ITU Recommendation E.164 establishes

standards for numbering plans– Telephone numbers should not exceed 15

characters• North American Numbering Plan (NANP)

– Numbers are 10 digits long

Getting to the Local Loop (cont'd)

• Area code jeopardy and relief– Realignment – move areas from one area code

to another– Split – create a new area code– Three-way split – create two new area codes out

of one area code– Overlay – assign a new area code in the same

geographic area as an existing area code• Specified Numbering Scheme (SNS)

– Enables people in the U.K. to make calls using a uniform formula

Signaling Types

• Three types of signaling:– Rotary/pulse or multi-frequency (MF) – used on

rotary dial phones– Dual tone multi-frequency (DTMF) – generated

by touch-tone pads on all standard phones– Digital – does not process audible tones

RJ-11 Connectors and Wiring

RJ-11 Connectors and Wiring (cont'd)

• Telephone jacks constitute a tip and ring• Tip

– The "transmit" wire– The positive side of the circuit (in relation to the

ring)• Ring

– The "receiving" wire– The negative side of the circuit (in relation to the

tip)

RJ-12 Modular Connector

RJ-11 Wall Connector Wiring

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

Summary

Explain the importance of a demarcation point in telephony

Identify signaling types used in the local loop Use numbering standards, including the North

American Numbering Plan (NANP) and United Kingdom standards

Explain how the local loop is wired Wire RJ-11 and RJ-12 connectors Wire BT-431A and BT-631A connectors Wire a wall jack and a line jack unit


Lesson 3:Infrastructure Issues and Standards

Objectives

• List common telephony connectivity and safety issues

• Identify safety procedures• Explain safety standards• Determine the proper cabling procedures for

specific environments• Identify various cable terminations• Wire an RJ-45 connector• Explain the importance of plenum cabling• Explain the necessity of securing equipment

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

– Return on investment (ROI) – the calculations made to ensure that equipment will result in company profitability

• Telecommunications reliability and safety issues:– Extreme temperatures– Vibration and shock– Humidity– Fire– 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– Line filters– Shielding– Ensuring proper humidity

• Personnel safety concerns and procedures

Network Equipment Building System

• Network Equipment Building System (NEBS)– Protects people and property – Ensures operational continuity in the telephony industry

• NEBS sets standards for the operation of telephony equipment with respect to:– Earthquake zones– Operating conditions and transport conditions– Levels of contaminants

• NEBS standards documents– GR-63-CORE (Physical Protection)– GR-1089-CORE (Electromagnetic Compatibility and

Electrical Safety)

Standards BodiesStandards bodies provide telephony standards

– Independent Committee for the Supervision of Standards of Telephone Information Services (ICSTIS)

– International Organization for Standardization (ISO)

– Independent Testing Laboratory (ITL) – European Telecommunications Standards

Institute (ETSI) – Federal Communications Commission (FCC) – Telecommunications Industry Association (TIA) – Electronic Industries Alliance (EIA) – British Standards Institute (BSI)

Proper Cabling Procedures

When pulling cable:– Avoid sharp bends in the cable – Take care to eliminate sharp edges in conduits

and other areas where cable might get worn or cut

– Make sure that wiring does not interfere with mechanical equipment

– Avoid passing wire close to fluorescent lights – Ensure that you are using the right type of cable

for a particular job

Choosing the Proper Cable

• American Wire Gauge (AWG) standard

• Standard gauges– 22 AWG – floor or wall cable– 24 AWG – backbone and drop cable– 26 AWG – drop cable and devices that pass data

between similar devices (daisy chaining)• The EIA/TIA 568 standard is the most commonly

used for twisted pair cabling

IBM Cabling Standard

RJ-45 connector – an eight-pin modular cable ending used in Ethernet networks

Crossover cabling – allows two systems to communicate without the use of an intermediary device, such as an Ethernet hub

WO O WG Be WBe G WBr Br

1 2 3 4 5 6 7 8

Serial Cable Termination

• Data terminating equipment (DTE) – a serial device that transmits and receives data digitally

• Data communications equipment (DCE) – a device that is attached to a communications line and is capable of altering a signal in transit

• RS-232 – a standard that enables DTE and DCE devices to communicate

• Universal Asynchronous Receiver-Transmitter (UART) – translates parallel communication into serial

• Additional ITU communication standards– V.24 through V.90

PVC vs. Plenum Cabling

• Plenum – the space above a dropped ceiling or behind a wall

• UTP or STP cables have a polyvinyl chloride (PVC) jacket (emits toxic gas when burned)

• When installing cable in a plenum:– Encase UTP or STP cable in a protective metal

conduit– Use plenum cabling (has a Teflon jacket that

inhibits burning)

Securing Equipment

• Physically secure telephony equipment using brackets

• Isolate power sources by grounding them properly– PBX grounding: a steel rod 6 feet (2 meters)

underground to which you attach the PBX ground lead

Summary

List common telephony connectivity and safety issues

Identify safety procedures Explain safety standards Determine the proper cabling procedures for

specific environments Identify various cable terminations Wire an RJ-45 connector Explain the importance of plenum cabling Explain the necessity of securing equipment


Lesson 4:Troubleshooting

Objectives

• Identify common troubleshooting tools• Use a line test handset (butt set)• Use a tone and probe kit• Use a digital multimeter• Use a line tester• Discuss how to troubleshoot analog lines• Discuss how to troubleshoot digital lines• Discuss telephony power issues

Troubleshooting Terms

• Short (continuity)• Open (open fault)• Terminator• Cross• Polarity

• Split• Line imbalance• 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 analog butt sets 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


• Multimeter– Measures resistance, current and voltage in an

electrical circuit


• Punchdown tool– Inserts wires in 66 and 110 punchdown blocks

• Line tester– Determines if a short exists in a line

• Laptop computer– Connects to a telephony network and uses

packet sniffers to troubleshoot lines• Additional devices

– ABS– DTMF decoder– Acoustic coupler– Modular breakout adapter

Troubleshooting Analog Lines

• PBX and ground-start analog lines– At the PBX, use a butt set to isolate crosstalk to

determine if 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 multimeter to measure for AC voltage

– AC voltage > 1 volt = improper grounding

Troubleshooting Digital Lines

• Improper clocking configuration– Voice and data lines must be precisely

synchronized using the CO's PRS– Use a butt set to check for improper clocking

• Check the Service Profile Identifier (SPID)– No connection will occur if the SPID is missing

or incorrect– SPID = area code + 7-digit phone number +

ISDN number• 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– Multimeter– Oscilloscope– Network analyzers– Time domain reflectometer (TDR)– Service-specific test set

Telephony Power Issues

• Grounding/earthing– When connecting telephony and LAN-based equipment,

ensure that all systems have only one ground path– Use an earth loop tester to avoid grounding problems– Ensure that power is connected properly at the electrical

termination device (circuit breaker)• Physical security

– Place all equipment in a dedicated server or CTI room• Telephones and ring voltage

– REN value determines the ringing voltage– -90 v AC charge needed to ring a standard analog

telephone

Summary

Identify common troubleshooting tools Use a line test handset (butt set) Use a tone and probe kit Use a digital multimeter Use a line tester Discuss how to troubleshoot analog lines Discuss how to troubleshoot digital lines Discuss telephony power issues


Lesson 5:Analog and Digital Signaling

Objectives

• Describe signaling categories and audible progress tones

• Compare and contrast in-band and out-of-band signaling

• Describe analog signaling in regard to E&M,loop-start and ground-start trunks

• Describe digital signaling, including T1 and ISDN lines

• Describe the nature and functions of Private Integrated Services Networks (PISNs)

• Discuss Signaling System Seven (SS7)• Describe Computer-Telephone Integration

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

• Audible call progress tones:– Dial tone– Busy signal– Receiver off hook too long– Nonexistent number

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

Analog Signaling

• Ear and mouth (E&M) signaling– Separate signaling wires for voice and data

Analog Signaling (cont'd)

• Grounding on E&M lines– Immediate start– Wink start– Delay-dial start

• Reducing E&M trunk glare with wink starting

Loop-Start Analog Trunk Signaling

Ground-Start Analog Trunk Signaling(Idle and Outgoing Calls)

Ground-Start Analog Trunk Signaling(Incoming Calls)

Digital Signaling

• T1 lines and in-band signaling– Channelized T1 – 24 channels of 56 Kbps for

voice and data– Unchannelized T1 – 1.536 Mbps for voice and

data• Bit robbing

– The practice of using the least significant portions, or bits, of a data or voice channel for signaling

– The T1 Superframe (SF) robs the A and B bits for signaling

– The Extended Superframe (ESF) has four bits (A, B, C and D), though only A and B are used

Digital E&M Signaling

A and B bit settings for sending and receiving switches:– Idle – A and B bits

are set to 0 for both switches

– Call initiation – switch A sets bits A and B to 1; switch B sets bits A and B to 0

– Call completion – both switches have the A and B bits set to 1

Digital Ground and Loop Starts

• When an FXS is idle:– The CO's A and B bits = 1– The PBX's A bit = 0; the B bit = 1

• When a digital loop-start line is in an idle state:– The A bits for the CO/FXO and PBX/FXS = 0– The B bits for the CO/FXO and PBX/FXS = 1

• When an FXS or PBX makes an outgoing call:– The CO/FXO's A bit = 0; the B bit = 1– The PBX/FXS's A bit = 1; the B bit = 1

Integrated Services Digital Network (ISDN)

• ISDN can carry voice, FAX, imaging or data communications

• Two types of ISDN:– ISDN Basic Rate Interface (BRI) – Two 64-Kbps

channels for voice or data; one 16-Kbps channel for signaling

– ISDN Primary Rate Interface (PRI) – 23 64-Kbps channels for voice or data; one 16-Kbps channel for signaling

• B channel (bearer channel) – carries voice or data• D channel (delta channel) – carries signaling• H channel – combined B channels

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 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)

PISN, showing connections via two different PINX types

Private Integrated Services Network (PISN)

(cont'd)

• A PISN consists of the following:

– End nodes – provide specific services, including voice and data

– Transit (transport) nodes – provide routing services to ensure that calls and network requests arrive at the proper destination

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

• High Level Data Link Control (HDLC) – a protocol that divides signaling data into discrete packets– HDLC allows three categories of stations (entities) to

communicate:• Primary – initiates and controls communication• Secondary – responds to communication• Combined – controls and responds to communication

HDLC frame

Signaling System Seven (SS7) (cont'd)

• SS7 elements:– Service Switching Point (SSP)– Signaling Transfer Point (STP)– Service Control Point (SCP)

• SS7 message types:– Initial Address Message (IAM)– Address Complete Message (ACM)– Answer Message (AM or ANM)– Release Message (REL)– Release Complete (RLC)

Computer-Telephone Integration (CTI)

CTI – the ability for telephony networks and data networks to share data

Summary

Describe signaling categories and audible progress tones

Compare and contrast in-band and out-of-band signaling

Describe analog signaling in regard to E&M, loop-start and ground-start trunks

Describe digital signaling, including T1 and ISDN lines

Describe the nature and functions of Private Integrated Services Networks (PISNs)

Discuss Signaling System Seven (SS7) Describe Computer-Telephone Integration

Telephony Networking

Telephony Essentials Investigating the Local Loop Infrastructure Issues and Standards Troubleshooting Analog and Digital Signaling

telephony networking

Documents

telephone services

local exchange carrier

milesthe local loop

multiple telephone numbers

longdistance calls

longdistance services

longdistance switchclass

ilecsinterexchange carrier