Transcript Document

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)
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 analogue setup messages,
safety practises and standards, crosstalk, split, line
imbalance, open, short, earthing issues, echo
cancellation in two-wire-to-four-wire hybrids)
Telephony Networking
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
Telephony Networking
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 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 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)
Telephony Networking
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
Telephony Networking
Elements of Computer-Telephony
Integration (CTI)
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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 centre”
Telephony Networking
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
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 public exchanges,
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 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
Telephony Networking
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
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 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)
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 analogue setup messages, safety
practises and standards, crosstalk, split, line imbalance,
open, short, earthing 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,
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])
Telephony Networking
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
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
BT-431A Connectors
Telephony Networking
BT-631A Connectors
Telephony Networking
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
Telephony Networking
Wall Jack Wiring Diagram
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 earthing them
properly
– Earthing ring
– Earthing lugs
– Steel rod placed roughly 2 metres in the
earth
Telephony Networking
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])
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
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)
Telephony Networking
Troubleshooting Terms
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Short (continuity)
Open (open fault)
Terminator
Cross
Polarity
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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 analogue 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)
• Multimetre
– 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 a BT-431A, RJ-11 or
RJ-45 jack into individual, easily accessible wires
Telephony Networking
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
Telephony Networking
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-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
– Multimetre
– Oscilloscope
– Time domain reflectometre (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
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
Telephony Networking
Summary
 Resolve problems when connecting time
division multiplexing (TDM) networks (e.g., inband 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 twowire-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)
Telephony Networking
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-tofour-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 Analogue Trunk Signaling
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) – 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
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
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
HDLC frame
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 analogue setup
messages, safety practises and standards,
crosstalk, split, line imbalance, open, short,
earthing issues, echo cancellation in two-wire-tofour-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
Analogue and Digital Signaling
Telephony Networking