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 center or contact center,
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)
Telephony Networking
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-ofband signaling, digital and analog setup messages,
safety practices and standards, crosstalk, split, line
imbalance, open, short, grounding issues, echo
cancellation in two-wire-to-four-wire hybrids)
Telephony Networking
Analog to Digital
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)
• G.711 – international standard for encoding
voice on a 64-Kbps channel
Telephony Networking
CO Connections
• Point of presence (POP) – an interexchange
carrier that connects long-distance services to
a local connection
• Private Branch Exchange (PBX) – enables an
organization to create an internal telephonenumbering system
• Direct Inward Dialing (DID) / Direct Dialing
Inward (DDI) – enables multiple telephone
numbers to be used on a few lines
Telephony Networking
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
Telephony Networking
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
Telephony Networking
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
Telephony Networking
Call / Contact Centers
• Centralized office used for processing a large
volume of calls
• Companies use call centers 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 centers allow for interaction with
agents via phone, e-mail, chat or instant
messaging, and Web (click-to-talk)
Telephony Networking
Call / Contact Center 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
Telephony Networking
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
Telephony Networking
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 center”
Telephony Networking
Trunks and Signaling
• Analog loop-start trunks used in most
standard home phones
• Ground-start trunk lines often used to
connect a PBX to a CO
Telephony Networking
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 longdistance providers, but now largely out of
use
– Stratum 3/3E – used by local switches,
gatekeepers and gateways
– Stratum 4 – used by PBXs and telco
channel banks
Telephony Networking
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
Telephony Networking
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
Telephony Networking
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
Telephony Networking
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 center or contact center,
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)
Telephony Networking
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 analog setup messages, safety
practices and standards, crosstalk, split, line imbalance,
open, short, grounding issues, echo cancellation in two-wireto-four-wire hybrids)
Telephony Networking
Lesson 2:
Boundaries, Numbers, Wiring
and Safety
Objectives
• Identify and use appropriate troubleshooting tools
(e.g., four-pair tester, tone-and-probe kit, analog
and/or digital butt set, volt meter, time domain
reflectometer)
• Identify safety procedures for working with
convergent network equipment (e.g., power,
proper grounding, electrostatic discharge [ESD],
radio frequency interference [RFI],
electromagnetic interference [EMI])
Telephony Networking
Demarcation Point
• Demarcation point (“demarc”)
– 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
Telephony Networking
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
Telephony Networking
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
Telephony Networking
RJ-11 Connectors and Wiring
Telephony Networking
RJ-12 Modular Connector
Telephony Networking
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
Telephony Networking
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
Telephony Networking
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
Telephony Networking
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
Telephony Networking
Testing Laboratories
• Testing laboratory rooms and equipment
– Fire, heat, humidity and moisture
– Airborne contaminant
– Electromagnetic
– Shakers
– Wind and rain
– Pressure
– Sound
Telephony Networking
Securing Equipment
• Physically secure telephony equipment using
brackets
• Isolate power sources by grounding them
properly
– Grounding lugs
– Steel rod placed roughly 6 feet in the
ground
– Earthing ring
Telephony Networking
Summary
 Identify and use appropriate troubleshooting
tools (e.g., four-pair tester, tone-and-probe kit,
analog and/or digital butt set, volt meter, time
domain reflectometer)
 Identify safety procedures for working with
convergent network equipment (e.g., power,
proper grounding, electrostatic discharge
[ESD], radio frequency interference [RFI],
electromagnetic interference [EMI])
Telephony Networking
Lesson 3:
Troubleshooting
Objectives
• Resolve problems when connecting time
division multiplexing (TDM) networks (e.g., inband and out-of-band signaling, digital and
analog setup messages, safety practices and
standards, crosstalk, split, line imbalance, open,
short, grounding 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,
analog and/or digital butt set, volt meter, time
domain reflectometer)
• Identify symptoms of improper clocking
configuration (e.g., problems with
synchronization)
Telephony Networking
Troubleshooting Terms
•
•
•
•
•
Short (continuity)
Open (open fault)
Terminator
Cross
Polarity
•
•
•
•
•
Split
Line imbalance
Crosstalk
Loopback testing
End-to-end testing
Telephony Networking
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 set to listen to digital
communications by going into "data safe mode"
Telephony Networking
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
Telephony Networking
Troubleshooting Tools (cont'd)
• Multimeter
– Measures resistance, current and voltage in an
electrical circuit
Telephony Networking
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 an RJ-11 or RJ-45 jack into
individual, easily accessible wires
Telephony Networking
Troubleshooting Analog Lines
• PBX and ground-start analog 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 multimeter to measure for AC
voltage
– AC voltage > 1 volt = improper grounding
Telephony Networking
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
• Crossed signaling methods
– Lines that use in-band signaling should not be
directly connected to lines that use out-ofband signaling
– Failed transmissions or garbled data can result
• Check for proper termination
• Be aware of different ISDN voice-encoding
standards
Telephony Networking
Troubleshooting Digital Lines (cont'd)
• Consider signal-to-noise ratio
• Test equipment for digital networks
– Signal/spectrum analyzer
– Multimeter
– Oscilloscope
– Time domain reflectometer (TDR)
– Service-specific test set
Telephony Networking
Troubleshooting Digital Lines (cont'd)
• Telephones and ring voltage
– REN value determines the ringing voltage
– -90 v AC charge needed to ring a standard
analog telephone
– Telco will not guarantee a phone to ring if a line
has to service a number of devices that
together constitute more than 5 REN in North
America (4 REN in the UK)
• Safety
– Ensure that power is connected properly at the
electrical termination device.
– Use a circuit breaker to guard against electrical
shocks
Telephony Networking
Summary
 Resolve problems when connecting time
division multiplexing (TDM) networks (e.g., inband and out-of-band signaling, digital and
analog setup messages, safety practices and
standards, crosstalk, split, line imbalance, open,
short, grounding 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,
analog and/or digital butt set, volt meter, time
domain reflectometer)
 Identify symptoms of improper clocking
configuration (e.g., problems with
synchronization)
Telephony Networking
Lesson 4:
Analog 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 analog setup
messages, safety practices and standards,
crosstalk, split, line imbalance, open, short,
grounding issues, echo cancellation in two-wireto-four-wire hybrids)
• Define the Q.931, Q.932, I.430 and Q.921/Highlevel Data Link Control (HDLC) standards,
including identifying the typical call progress
signals (e.g., alerting, call proceeding, etc.)
Telephony Networking
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])
Telephony Networking
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
Telephony Networking
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
Telephony Networking
Loop-Start Analog Trunk Signaling
Standard
phone/PBX
CO
Tip (green)
Ring
generator
Ground
Battery
-48 v DC
Idle
condition
Ring (red)
Standard
phone/PBX
CO
Tip (green)
Ring
generator
Ground
Battery
-48 v DC
Ring (red)
Making
a call
from a
standard
phone
Telephony Networking
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) – 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
Telephony Networking
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
Telephony Networking
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
Telephony Networking
ISDN Protocols (cont'd)
Q.931 message types
Message Type
Description
Setup (SETUP)
Begins data transmission
Connect (CONNECT)
Allows terminal adapters and switches to signal
each other for the call to proceed
Call proceeding
(CALL PROC)
Sent by the switch to the terminal that initiated
the call
Alert (ALERTING)
Used to send a signal to the calling system
Connect acknowledgement
(CONNECT ACK)
Sent by the terminal being called to
acknowledge that the call has been established
Telephony Networking
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
Telephony Networking
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
Telephony Networking
PISN Signaling Methods (cont'd)
• QSIG basic call (QSIG BC)
Telephony Networking
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
Telephony Networking
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
Telephony Networking
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
Telephony Networking
Computer-Telephony
Integration (CTI)
CTI – the ability
for telephony
networks and
data networks
to share data
Telephony Networking
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 analog setup
messages, safety practices and standards,
crosstalk, split, line imbalance, open, short,
grounding issues, echo cancellation in two-wireto-four-wire hybrids)
 Define the Q.931, Q.932, I.430 and Q.921/Highlevel Data Link Control (HDLC) standards,
including identifying the typical call progress
signals (e.g., alerting, call proceeding, etc.)
Telephony Networking
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 Networking


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Telephony Essentials
Boundaries, Numbers, Wiring and Safety
Troubleshooting
Analog and Digital Signaling
Telephony Networking