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The “ABCs” of ADSL Service Installation
With the right tools and a bit of know-how, virtually
any technician can perform an asymmetric digital subscriber
line (ADSL) service installation. This document is designed
next level solutions
to simplify the job, providing an introduction to DSL
technology, a step-by-step overview of the installation
process, as well as valuable guidelines for
troubleshooting. Since each carrier is likely to have
different deployment strategies and procedures,
the purpose is to provide background
information and review conventional
installation practices. The illustrations and
explanations are intended to serve only as
a supplement to established methods
and procedures, and to enhance
the skills and abilities of
installation technicians.
Table of Contents
DSL Background ............................................................ 3
ADSL Installation ...........................................................7
DSL Limitations.............................................................. 3
Loop Prequalification ..................................................... 7
Propagation Loss............................................................. 3
Step-by-Step Provisioning To The NID .......................... 7
Crosstalk or Metallic Noise ............................................ 3
Customer Site Installation ............................................. 10
Bridged Taps ................................................................... 4
ADSL Modem Installation ............................................ 10
Load Coils ....................................................................... 4
End-To-End Testing (Final Step) ...................................11
External Electromagnetic Interference ........................... 4
Troubleshooting ............................................................ 11
ADSL Service Overview .................................................. 5
Information Gathering ................................................... 11
Why ADSL? .................................................................... 5
Potential Failures at the Customer Premises ..................11
Network and Outside Plant Infrastructure ...................... 5
Potential Failure Sources in the Copper Loop .............. 12
ADSL Installation From the NID
(a.k.a., ONI or SID) to the Customer Premises .............. 6
Poor POTS Performance on an ADSL Line.................. 13
Acronyms
ADSL ..................................................... asymmetric DSL
ANSI ..................American National Standards Institute
ATM ....................................asynchronous transfer mode
CAP ................. carrierless amplitude/phase modulation
CLEC ...................... competitive local exchange carriers
CO................................................................ central office
COLO ............................................................. collocation
CPE ..................................customer premises equipment
DLC .................................................... digital loop carrier
DLC-COT ..... digital loop carrier central office terminal
DLC-RT .................. digital loop carrier remote terminal
DSL................................................ digital subscriber line
DSLAM ..........digital subscriber line access multiplexer
DMT ................................ discrete multitone modulation
G.DMT ............ ITU standard for ADSL encoding based
on discrete multi-tone modulation (DMT)
G.Lite .............. an ADSL standard that doesn’t require a
permanent data/voice splitter
HDSL, HDSL-2 ... high bit-rate symmetric DSL services
IDSL ..................................................... ISDN-based DSL
ISDN ....................... Integrated Services Digital Network
ISP ............................................ Internet service provider
ITU ............... International Telecommunications Union
IW ................................................................ inside wiring
MDF .......................................... main distribution frame
Microfilter ............. low-pass line filter required on each
telephone set with G.Lite service
NEXT ................................................. near-end crosstalk
NID (a.k.a., ONI or SID) ......... network interface device
NOC ....................................... network operations center
PSTN ........................ public switched telephone network
POTS ..................................... plain old telephone service
RADSL ................................................rate-adaptive DSL
SDSL ....................................................... symmetric DSL
Splitter ............................................. ADSL/POTS splitter
TDR ....................................... time-domain reflectometry
X-Box ............................................. cross-connection box
—2—
The “ABCs” of ADSL Service Installation
DSL Background
dependent on the condition of the copper loop and the spectral
Digital subscriber line (DSL) is a generic term used to
compatibility with other services carried in the wire bundle.
describe a wide range of data transmission technologies using
Critical factors affecting the loop’s suitability are line balance
standard copper telephone wiring (i.e., “last mile” local
and loading. Voice-grade repeaters and load coils can
loops). Generally, DSL can be classified as either asymmetric
severely degrade transmission characteristics of high
or symmetric. Asymmetric DSL (ADSL) yields higher data
frequency DSL signals, putting additional restrictions on loop
throughput downstream (from the network to the end user)
length, bridged taps, and spectral compatibility with other
than upstream. Symmetric DSL (SDSL), on the other hand,
services in the wire bundle.
provides the same transfer rate in both directions, making it
more suitable for applications like business networks, Web
Propagation Loss
servers, and users that transmit and receive data in roughly
A primary limitation for DSL service is cable propagation
equal amounts.
loss, which can reduce the maximum bit rate. Propagation
loss varies unpredictably as a function of frequency, and is
DSL services commonly deployed in the U.S. today include
typically caused by poor splices, low-quality drop cable, or
ADSL, SDSL, HDSL (High bit-rate symmetric DSL), and
water ingress.
IDSL — a hybrid of DSL and ISDN (Integrated Services
Crosstalk or Metallic Noise
Digital Network). Table 1 summarizes the most common
Crosstalk or metallic noise consists of signals that are coupled
DSL variations in use today.
to the DSL signal on the intended service pair. The source
DSL Limitations
may be other pairs in the binder group or even pairs in
Ultimately, the ability to provide DSL service to a subscriber,
adjacent binder groups. Ideally, if capacitances are perfectly
as well as the quality and maximum data rate of the service, is
balanced between each wire in the pair and the rest of the
cable, all disturbing
signals will couple
Table 1: Prevailing DSL Technologies
equally and the
DSL Service
Speed(s)
Max. Loop
Length (ft)
Notes
G.Lite or “splitterless”
ADSL (asymmetric)
1 to 1.5 Mbps downstream,
64 to 384 Kbps upstream
18,000
Based on carrierless amplitude phase (CAP) encoding.
G.DMT or “full-rate”
ADSL (asymmetric)
0.5 to 8 Mbps downstream,
64 to 800 Kbps upstream
18,000
Based on discrete multitone (DMT) encoding. Requires a
“splitter” at customer premises to separate data and voice traffic.
RADSL (rate-adaptive
asymmetric DSL)
0.6 to 7 Mbps downstream,
128 to 1024 Kbps upstream
25,000
Same bandwidth as ADSL. Adjusts speed on the fly to match
line quality, like an analog modem.
HDSL (high bit-rate
DSL, symmetric)
768 to 1.5 Mbps,
(2 Mbps with three lines)
12,000
Requires two wire pairs. Often used as an alternative to T1
service. Longer distances can be supported with a signal repeater.
SDSL
(symmetric DSL)
384 to 768 Kbps
10,000
The forerunner to HDSL-2. Common configurations include
784 Kbps (2B1Q line coding) and 400 Kbps (CAP line coding).
HDSL-2
(symmetric)
1.5 - 2 Mbps
12,000
The same performance as HDSL, but uses a single phone line.
Longer distances can be supported with a signal repeater.
IDSL (ISDN
DSL, symmetric)
144 Kbps
18,000
Uses the same 2B1Q line coding as ISDN. Bypasses the
congested phone network — a big plus. Can handle distances
up to 30,000 feet with signal repeaters.
resulting signal will
be zero. Ultimately
though, some signal
—3—
bleed occurs, and
the amount of
crosstalk increases
as a function of
higher frequency.
Crosstalk comes from a variety of
Table 2: Primary DSL “Disturbers”
sources or “disturbers,” and the
DSL Service
Primary
PrimaryDisturbers
Disturbers
severity of the affect is largely
ADSL G.DMT
SDSL (784K 2B1Q and 400K CAP), HDSL, ISDN/IDSL, T1, ADSL G.Lite, RADSL
dependent on the line coding used for
ADSL G.Lite
SDSL (784K 2B1Q and 400K CAP), HDSL, ISDN/IDSL, T1, RADSL
the specific service. In addition to
IDSL
NEXT,* ISDN, HDSL, 160K SDSL, 160K CAP SDSL, ADSL G.DMT and G.Lite
conventional services, crosstalk
HDSL
NEXT,* ISDN, SDSL, ADSL G.DMT and G.Lite
incompatibilities exists between
SDSL
NEXT,* HDSL, ISDN, ADSL G.DMT and G.Lite
different DSL services themselves
*Near-end crosstalk
Load Coils
(see table 2).
On long local loops, analog voice quality can deteriorate from
The noise from primary disturbers is measured across the
capacitive effects. This capacitance effect alters the phase of
entire band of frequencies used by the specific DSL service to
the current relative to the voltage on the loop (i.e., variations
ensure that crosstalk is not present within the modem’s power
in voltage go out of “synch” with corresponding variations in
spectral density. As little as -90dBm of noise can exclude
current). This effect limits the maximum power that can be
deployment of some DSL services.
delivered over the wire. Load coils can remedy this problem,
and improve analog voice quality. A load coil permits the
Surprisingly, a significant source of noise can come from
inductance of the line to be adjusted in just the right amount,
POTS lines. The voice signal poses no hazard, but the
so that the phase of voltage and current are resynchronized.
impulse noise created by the telephone going off-hook during
While this is great for voice service, load coils can cause
the ringing signal can momentarily disrupt a DSL signal,
serious problems for broadband services. Most load coils
requiring it to resynchronize. This problem is extremely
only condition the loop up to about 3,300 Hz. Signals over 4
difficult to isolate, since the ring-trip impulse could come
KHz become attenuated. Further, ADSL signals operating in
from a neighbor’s line. With ADSL service, a POTS splitter
the 25 KHz to 1100 KHz band are not allowed to pass through
or microfilters are used to reduce the impact of impulse noise.
the load coil with sufficient energy. Therefore, load coils
cannot be present on loops intended for ADSL services.
Bridged Taps
Bridged taps, or non-terminated pairs spliced onto the service
External Electromagnetic Interference
pair, pose another potential problem for DSL services.
In addition to noise from services in close proximity, other
Laterals connected to the main cable carry the same signals
potential external disturbers to DSL include impulse noise
transmitted on the main cable, causing a reflection to
from AC motors or electrical equipment located close to the
propagate from the end of the lateral back to the main cable.
customer premises equipment (CPE). Radio emissions from
At certain frequencies, the additive effects of these reflections
sources such as AM radio, analog cellular, and HAM radio are
can significantly reduce the integrity of the DSL signal. For
also a potential source of noise. These emissions are coupled
ADSL, less than 2,500 feet of bridged tap in total and less
to the pair as longitudinal or “common-mode” noise. Due to
than 200 feet per tap are recommended. For best
imperfections in balance, splices, or the cable, some of the
performance, bridged taps should be avoided within 1,000
longitudinal noise is converted to metallic noise.
feet of the network interface device or NID (Note: this is also
referred to as the outside network interface [ONI] or the
subscriber interface device [SID]).
—4—
ADSL Service Overview
Network and Outside Plant Infrastructure
Why ADSL?
In the outside plant, ADSL hardware installation varies
Generally, ADSL is the most suitable DSL service for
depending on the distance from the CO. For example, with
telecommuters or home-based users since much more data is
ADSL service the current specified limitation for the loop
typically downloaded than is transmitted, especially when
length is 18,000 feet, or a maximum of 1300 Ohms of
browsing the Internet. With ADSL equipment installed at
resistance. These length and impedance restrictions are due to
both ends of the local loop, standard voice service can coexist
copper’s vulnerability to noise interference as well as signal
with ADSL over the same copper pair, making the technology
propagation loss. For customers served by copper loops of
even more attractive for broadband data network access from
18,000 feet or less, ADSL service can be installed as
the home. Secondary line pairs are not required to provide
illustrated in figure 1.
Federally-mandated “lifeline” voice service.
The CO must be equipped with a digital subscriber line access
At the other end of the equation, competition from the cable
multiplexer (DSLAM) and a corresponding ADSL line card.
industry and exploding Internet usage are putting pressure on
The DSLAM converts incoming and outgoing data on the
telecommunications carriers to respond. These carriers are
carrier’s asynchronous transfer mode (ATM) backbone
turning to ADSL instead of other DSL technologies because it
network into high frequency ADSL signals, and vice-versa.
satisfactorily meets both their bandwidth requirements and
Furthermore, low frequency voice-band signals (POTS or
time-to-market needs.
plain old telephone service) can be transmitted over the same
copper wires as the ADSL signal, without causing any
ADSL is an exciting new service that will help carriers retain
interference (see figure 2).
customers and maintain a leadership role in the
Low Band
communication market. However, rolling out the service
High Band
Amplitude
presents a host of challenges since it typically reveals
limitations in the outside plant infrastructure that require
special attention by line technicians. Further, line technicians
must be made aware of the ways that ADSL service can affect
ADSL
Upstream
POTS
ADSL
Downstream
their work. For instance, how will ADSL technology impact
4 KHz
existing services already deployed?
20 KHz
1100 KHz
Frequency
Figure 2: This graph shows the typical allocation of frequencies
for high (ADSL) and voice (POTS) band signals on the local loop.
Main Distribution Frame
POTS
Switch
Splitter (for ADSL G.DMT service)
Voice Only
PSTN
Voice
ADSL
& Voice
ATM
Switch
CrossConnect
Box
Customer
Premises
Pedestal
Data
ATM
Central
Office
DSLAM
Max 18K Feet or 1300 Ohms
Network
Interface
Demarcation
Figure 1: This figure illustrates the simplest scenario for an ADSL installation, which requires a loop length of 18,000 feet or less AND
maximum impedance of 1300 Ohms.
—5—
Customers located further than 18,000 feet from the CO can
transmitted by a standard telephone set. The splitter regulates
get access to ADSL service if the neighborhood is served by
the change of impedance and capacitance inserted by the
digital loop carrier (DLC) extension. In this scenario, a
telephone and also prevents detrimental interactions between
DSLAM and voice/data splitter must be remotely located near
voice signal echoes and the ADSL modem, or visa-versa. The
or inside the remote DLC cabinet at the upstream termination
“off-hook” signals required to draw a dial tone can cause the
of the final copper loop as shown in figure 3. By
ADSL modem to lose synchronization.
multiplexing the data signals and then carrying them via the
DLC, ADSL availability can be offered over a much wider
The installation of an ADSL/POTS splitter requires a
service area. The remote DSLAM serves the same function
technician to be dispatched to the customer premises. In
as a CO-based DSLAM, except that it can be located many
addition to the cost of a “truck roll,” installing the inside
miles from the CO. The 18,000 foot and 1300 Ohm limits are
wiring can be confusing and time consuming. One alternative
still required for the final copper service tap, downstream
is the ITU’s G.Lite ADSL, which doesn’t require a splitter
from the remote DSLAM.
(see figure 4) and is therefore commonly referred to as
“splitterless” ADSL.
POTS
Switch
PSTN
DLC
CO
Terminal
Voice
Remote
DSLAM
& Splitter
DLC
Signals
ATM
Switch
ADSL
& Voice
Data
ATM
X-Box Pedestal
DLC-RT
Central Office
NID
Loop Extension
Max 18K Feet or 1300 Ohms
Figure 3: This schematic shows a typical ADSL installation for a digital loop carrier (DLC) service deployment. In this scenario, a remote
DSLAM and splitter are required in the outside plant.
Instead of the splitter, G.Lite ADSL requires the installation
ADSL Installation From the NID (a.k.a., ONI or
SID) to the Customer Premises
of low-pass microfilters between every telephone jack and
telephone set—a task that can be performed by the customer.
Between the CO and the NID, the copper loop carries both
The microfilter passes the low frequency voice signal to the
ADSL and voice signals. With G.DMT, the combined signal
telephone set without interruption to ADSL service. The
must be decoupled at the customer premises by an ADSL/
downside is that every telephone set requires a microfilter,
POTS splitter (see figure 4), which is installed inside or
and each telephone connection represents a bridged tap.
adjacent to the NID. The functional specifications required
for the splitter are outlined in ANSI T1.413, issue 2, as well as
the ITU’s G.DMT standards.
Downstream from the splitter, decoupled ADSL signals are
received or transmitted by an ADSL modem, which can take
the form of a standalone box or an internal card in the PC.
Similarly, the decoupled voice signal is received or
Some G.DMT service installations can be converted to G.Lite
by performing a simple software upgrade to the DSLAM and
ADSL modem, removing the ADSL/POTS splitter, and
adding microfilters. The feasibility of performing this
conversion must be verified with the CO facility as well as
checking the specific type of equipment deployed to the
customer premises.
—6—
Table 3: Standard line conditions required for ADSL service.
Condition
Specification
Maximum Loop Length
18,000 feet over 24 AWG wire, including bridged tabs
Impedance Relative to Signal Loss
Up to 1300 Ohms
Load coils
None
Repeaters
None
Bridged Taps
Less than 2500 feet total with no single tap greater than 1000 feet. Avoid bridged taps
within 1000 feet of the NID (a.k.a. ONI or SID).
Crosstalk or Metallic Noise
These faults can compromise the maximum bit rate of the line during synchronization,
and potentially cause service failure after synchronization.
Spectral Compatibility
Avoid placing jumpers near T1 or other higher-bandwidth services. Avoid using pair from
the same wire bundle that has T1 or other high bandwidth services.
Figure 4: This shows
typical in-house wiring
for G.DMT and G.Lite
ADSL service, showing
the location of a
splitter for G.DMT
and microfilters for
G.Lite.
G.DMT "Full-Rate" ADSL
G.Lite "Splitterless" ADSL
Customer
Premises
Customer
Premises
Microfilter
Tel
Tel
Microfilter
2nd Tel
NID
Voice
& ADSL
Splitter
Voice Only
ADSL
G.DMT
Modem
2nd Tel
NID
PC
Voice
& ADSL
ADSL
G.Lite
Modem
PC
ADSL Installation
frequency testing via existing Harris RTUs, providing
Loop Prequalification
accurate detection and measurement of high-frequency losses,
If possible, the network operations center (NOC) performs a
noise margins, bridged taps, impulse noise and longitudinal
series of pre-qualification tests to ensure that the copper loop
balance. This tool enables the CO technician to prequalify the
is of sufficient quality to handle ADSL service prior to
line for DSL service, and accurately predict the performance
dispatching a truck for final installation. These tests are
(or maximum bit rate) that can be achieved.
typically performed using a CO-based line test system, such
as the Lucent Mechanized Loop Test (MLT) or Harris Remote
Step-by-Step Provisioning To The NID
Test Unit (RTU). These systems can accurately predict the
After the CO has prequalified the copper pair and verified that
performance of analog service that can be provided on a given
the DSLAM is available for service, a technician will be
line. These tests commonly include AC/DC performance,
dispatched to complete the installation to the NID and the
resistive faults, loop length, draw break dial tone, and load
customer premises. With different deployment strategies and
coil detection.
service offerings (i.e., G.Lite versus G.DMT), carriers are
bound to have different procedures and requirements for
Unfortunately, DSL services operate at a higher and wider
ADSL service installation. With that in mind, the following
range of frequencies than voice service, meaning that
section represents the typical installation procedure. To
additional testing capabilities are required. Enhanced systems
complete an ADSL installation, the service technician will
such as the Harris Wideband Test Pack (WTP) permit high
require the equipment described in table 4.
—7—
Figure 5: This illustration sums up the entire ADSL installation process.
1. Prequalification
2. Provisioning up to the NID
3. Customer Premises
Installation
Bell CO
PC
NID
X-Box
Modem
Pedestal
Step 1
Install ADSL modem
Splitter
"Full-rate" ADSL with
Splitter
NID
NOC
Step 1
Line verification
Step 2
DSLAM
synchronization
test
Use CO Line
Test System to Prequalify
Pairs for DSL Services
Step 3
Verify Internet service by
opening browser
Step 3
Install splitter
if required
Bell
Step 4
Basic conditioning
supervision &
voice-grade service
tests
Microfilter
NID
Step 5
DSLAM
synchronization
& bit rate
confirmation
Step 4
Install microfilters (if required)
& verify POTS service
PC
Modem
“Splitterless” ADSL
Table 4: Representative tools required for an ADSL installation include an ADSL modem, splitter or microfilters,
handheld splitter, test meter, load coil detector, and a data safe butt set.
Tool
Function
This tool is used to verify end-to-end service turn up.
Handheld
ADSL Modem
A splitter is installed permanently near the NID for G.DMT ADSL. Microfilters are
required on the line of every voice device for G.Lite ADSL.
Microfilter
or Splitter
Handheld
Splitter
Test
Meter
This tool is used to troubleshoot a problem splitter or microfilter, or can be used to
safely draw dial tone on “splitterless” ADSL.
This device can be used to asses quality and troubleshoot inside wiring.
(digital multimeter recommended)
This tool is used to detect unwanted or misplaced loads.
Load Coil
Detector
Data-Safe
Butt Set
Short Range
TDR
This device is used to verify that the voice line works properly with ADSL.
Data lock-out feature is required to detect the presence of data being transmitted
before going off-hook.
Use this device to locate the distance of open, shorts, and unbalance lines in the
short distance.
—8—
Step 2
Configure PC
Step 1: Line verification and testing at the x-box
ADSL test set fails to establish synchronization with the
At the cross-connection box, verify that the correct copper
DSLAM, call the help desk to verify that the line has been
pair is assigned for service. Once the target service pair is
assigned to a DSLAM. If a synchronous connection is
identified, confirm that it is an unloaded and balanced pair
established, but the downstream or upstream bit rates are
using the load coil detector and the test meter. At this point,
either higher or lower than the requested service, contact the
use the test meter to perform the basic conditioning tests
help desk to confirm that the DSLAM has been configured
summarized in table 5. Confirm that a dial tone can be
correctly. Once again, qualify the facility using the basic
established by connecting a butt set across the line. No data
conditioning tests in table 5, then complete the cross connect,
should be detected using the data lock-out butt set, since the
and proceed to the NID.
far end modem will not be connected yet.
Step 3: ADSL/POTS splitter installation (G.DMT only)
Step 2: DSLAM “sync” and bit rate confirmation at the x-box
Locate the NID box at the customer premises, and install the
Terminate the service pair with an ADSL test set (ADSL
ADSL/POTS splitter in a convenient location (see figure 6).
“golden” modem emulation), turn on the power, and attempt
Set a jumper on the network port, then terminate the wire pair
to establish synchronization with the upstream DSLAM. If
for voice service on the voice port and the wire pair for ADSL
synchronization is achieved and the test set displays the
service on the data port.
required downstream and upstream bit rates, the DSLAM is
operating correctly and the line is ready for service. If the
NID
CO
Step 4: Basic conditioning, supervision, and voice-grade tests
ADSL
At the NID, basic conditioning tests (table 5) should be
POTS
performed once again. In addition, the supervision tests
should be performed to confirm that the circuit will support
high-speed ADSL data service. Finally, voice-grade service is
verified by connecting a butt set across the voice port, setting
it to “talk” mode, and listening for dial tone.
Network
Data
Voice
ADSL
Splitter
Step 5: DSLAM synchronization and bit rate confirmation at
the NID (a.k.a., ONI or SID)
(G.DMT Only) Terminate the data port on the splitter with an
ADSL test set, turn on the power, and once again confirm
Figure 6: This shows the location of the NID and permanent
ADSL/POTS splitter at the customer premises for ADSL G.DMT.
synchronization and required downstream and upstream bit
Table 5: Customary field tests for ADSL service installation. (Note: A CO-based conditioning device can improve the
efficiency of this process, allowing the technician to control conditioning of the line remotely.)
Function
Test
Notes
Basic Conditioning
• AC/DC Voltage
• Load Coil Count
• Resistance Fault (Ohms) • Hi-Resistance Open
• Capacitance (opens)
These are “dry circuit” tests that are performed with the
central office or remote terminal battery removed.
Supervision
• Current Flow
• Circuit Loss @ 1000Hz
• Power Influence
• Circuit Noise
These tests are used to determine if the cable facility
can support not only voice services, but more
importantly data service.
• Circuit Balance
• Station Protection Ground
• Slope Test
—9—
rates. If synchronization fails or the bit rates are lower than
the pair for data service to port number two (see figure 7).
required, contact the help desk.
Standard convention dictates that the pin out for the modem
should be connected to the second pair.
(G.Lite Only) For splitterless G.Lite ADSL installations, first
verify dial tone at the NID with a butt set. Disconnect the
G.Lite (splitterless ADSL)
butt set, terminate the pair with an ADSL test set, turn on the
The live line pair should carry both ADSL and voice service
power, and confirm synchronization and required downstream
on the same line. If necessary, rewire the jack to match the
and upstream bit rates.
modem pin out, or use a patch cord for pair conversion.
!! NOTE: A device called a “half ringer” is often installed at
ADSL Modem Installation
the NID by the incumbent carrier, and is used to identify the
There are three common ADSL modem configurations in use
far end of the line using the Lucent MLT system. The device
today. They include two external (with either Ethernet or
adds a known resistance that enables it to be detected.
USB interface to the PC) and an internal version with a PCI
Unfortunately, some devices introduce just enough line
interface. If the specified CPE is an internal modem, some
impedance to block the ADSL signal. As a precaution, half
PC knowledge or experience will be required to complete the
ringers should be removed from the NID prior to installing
installation.
inside wiring or CPE.
!! NOTE: Some types of inside wiring (e.g., IW flat wires)
Customer Site Installation
cannot support more than one service, and should be replaced
Determine where the customer wants to connect their PC to
with Category 3 twisted pair wiring.
ADSL service. Find the location of the nearest phone jack in
the room and verify that the line pair is active.
External ADSL modem with Ethernet interface
If the specified CPE is an external modem with Ethernet
G.DMT (permanent splitter)
interface, an Ethernet-ready connection must be available on
If the customer does not require voice on the existing phone
the PC to complete the installation. If not, this capability will
jack, jump the same pair assigned to the data port at the NID.
need to be added by installing a Ethernet network interface
If the customer requires voice and ADSL service, install a
card (NIC) in the PC.
dual port wall jack if one is not already available. Confirm
that the pair for voice service is on port number one and jump
Once Ethernet capability is confirmed or installed on the PC,
verify that the Ethernet connectors on the PC will be
compatible with the Ethernet patch cord (Note: RJ-45
Voice
Pair
RJ11
connections are the most prevalent used for Ethernet today,
but some older computers have different connectors that will
Port 1
1
2
3
4
5
ADSL
Pair
Port 2 (Data)
RJ11 or
RJ45
require an adapter.) Once cord connector compatibility is
6
1
2
3
4
5
6
confirmed, install the Ethernet patch cord between the modem
and the Ethernet port on the PC. Then connect a patch cord
between the modem and the wall jack data port and install the
appropriate software drivers on the PC.
Figure 7: Schematic showing the pinouts for ADSL and voice
service in a dual-jack G.DMT installation.
— 10 —
External ADSL modem with USB interface
Once the IP address is configured correctly, test the
If the CPE is an external ADSL modem with a USB interface,
connection by launching an Internet browser. At this point,
the USB port on the PC should already be activated. Connect
the default home page should load, indicating a successful
a USB cable between the ADSL modem and the PC, connect
end-to-end connection with the ISP.
a patch cord between the modem and the wall jack data port,
and install the appropriate software drivers on the PC.
POTS
After the end-to-end ADSL service verification, the technician
Internal ADSL modem with PCI interface
should also verify the telephone service in the house. Keep in
If the specified CPE is an internal ADSL modem with a PCI
mind that the ADSL service should be unaffected by the
interface, the only requirement is that an empty PCI slot is
telephone service. See the section in troubleshooting if
available in the PC. (NOTE: When working inside a PC, it is
failure or loss of quality are noted for telephone service.
critical that proper grounding procedures be observed,
including wearing a properly grounded electrostatic discharge
Troubleshooting
(ESD) wrist strap. In addition, prior to opening the computer
Information Gathering
enclosure, the PC and all connected devices should be turned
Problems discovered during or after ADSL service installation
off and their power cords disconnected.) Install the ADSL
may require the technician to locate failures in either the CPE
modem card in an empty PCI slot in the PC. Connect a patch
or wiring. When trouble is reported, it is critical that a
cord between the modem and wall jack data port, turn on the
detailed description of the problem be documented before
computer and install the software driver on the PC.
troubleshooting. For example, customers have been known to
forget to turn on the modem. On other occasions, problem
End-To-End Testing (Final Step)
resolution may require cutting over a new line because of
ADSL
marginal quality on the original line. Table 6 summarizes
Turn on the modem (external only) and PC. Configure the PC
four basic questions that should be answered before
according to the specific requirements of the Internet service
troubleshooting ADSL service problems.
provider (ISP). At this point, a permanent or dynamic IP
address may need to be set up on the PC. (NOTE: It is
Potential Failures at the Customer Premises
recommended that the installation technician become familiar
Once the basic problems covered in table 6 have been ruled
with setting up the PC by consulting with the technical
out, further troubleshooting should start at the customer
support staff at the ISP or else the ADSL help desk before
premises. If the modem maintains a good connection with the
attempting this portion of the installation.)
DSLAM, begin by looking for the problem on the PC. The
customer may have changed a setting or the IP address
If the external modem includes a “sync” LED, it should
accidentally — a common problem when installing a
indicate that the modem has established a connection with the
network-related application using the “default” configuration
DSLAM (on most ADSL modem equipment, the sync LED
option. If the problem still exists, call the ADSL help desk to
will flash amber on power up and then change to solid green
verify that the account is still active and to check for any
to indicated network synchronization with the DSLAM). For
recent deactivations or work done on the network in the same
internal modems, the software driver usually includes some
neighborhood.
type of on-screen status icon that can be used to monitor the
activity of the modem. Documentation included with the
modem can be should be helpful here.
— 11 —
Table 6: Four fundamental questions that should be answered prior to troubleshooting ADSL service.
Question
If Yes
If No
Is voice service still functioning on the line?
The problem is probably limited to the
ADSL service.
The problem is on the line (i.e., an open circuit).
Does the modem indicate synchronization
with the DSLAM?
The problem is probably an incorrect
configuration on the PC, or a failure in
the ISP network.
Isolate the failure using an ADSL test set.
Does the modem work sporadically or only
at certain time of the day?
There may be periodic radio frequency
(RF) interference from equipment or other
high frequency sources. Contact the
ADSL help desk and try reconfiguring the
line with better noise margin (this may
also decrease the maximum connection
speed and effective bit rate).
Isolate the failure using an ADSL test set.
(External Modem only) Is the modem
correctly connected to the PC and the
power turned on?
Isolate the failure using an ADSL test set.
Reconnect the modem and turn it on.
If a problem with the PC can be ruled out, disconnect the
the loop for loading, bridged tabs, resistive faults, or
modem from the wall jack, terminate the line with an ADSL
unbalanced capacitance pair.
test set and run a modem emulation test. If the ADSL test set
synchronizes with the DSLAM, the customer’s ADSL modem
When all else fails, and the decision is made to cut over
may be defective. Connect another ADSL modem and try to
another line to repair the problem, ensure that the line has
establish a connection.
been prequalified for bridged taps and other required
conditions, and that load coils are not present. Basic
If terminating the line with an ADSL test set fails to establish
conditioning and supervision tests should then be run on the
synchronization with the DSLAM (when connected at the
new line (see table 5). As a rule of thumb, run a modem
same point as the customer’s modem), try to isolate the failure
emulation test with the ADSL test set at the customer site
between the wall jack and the NID. If the ADSL test set
before closing the repair ticket. This will ensure the line has
synchronizes with the DSLAM when connected at the NID,
been properly terminated for service.
the inside wiring is the culprit. Confirm the severity of the
failure with a test meter and run new wire to the wall jack if
!! Note: Poor bit rate performance may be caused by an
necessary.
excessive number or length of bridged taps in the house. This
is especially common with splitterless ADSL, which utilizes
Potential Failure Sources in the Copper Loop
bridged taps for voice service. The bit rate can be improved
If problems at the customer premises can be ruled out, and the
by shortening or reducing the number of bridged taps, or by
ADSL test set fails to synchronize with the DSLAM at the
installing a permanent ADSL/POTS splitter. However, the bit
NID, the problem is probably in the outside plant. Perform a
rate should first be verified at the NID and the ADSL jack to
modem emulation test with the ADSL test set terminated on
determine if the limitation is caused by inside wiring or the
the line at the next upstream access point on the loop (i.e.,
outside plant loop conditions. If the exhibited bit rate is
probably a cross-connection box, a pedestal, or an MPOLE).
significantly better at the NID, then inside wiring or bridged
Continue to the next upstream access point until a successful
taps are most likely the problem, and the method described
connection is acquired. At the point where a successful
above may help (see figure 8).
connection is established, check the downstream portion of
— 12 —
Poor POTS Performance on an ADSL Line
“Splitterless” ADSL
with laterals installed
If the telephone service is inactive, but the ADSL service is
working properly, verify the dial tone with a portable ADSL
Microfilters
splitter and data safe butt-set at the next upstream access point
Lateral
(see figure 9). Reduce the trouble area and look for
continuity on the pair. In the case of one open line, the ADSL
Lateral
service may still be functioning. The DSLAM and the ADSL
Lateral
NID
ADSL G.Lite
Modem
modem are self-powered, unlike POTS service, which relies
PC
on power from the CO (typically 48V DC) and requires the
tip and rings to be grounded. The short range TDR can be
used to locate the fault, and then repaired.
Pedestal or NID
“Full-rate” ADSL
with data line isolated from voice lines
ADSL
Splitter
Data
POTS
NID
Splitter
ADSL G.DMT
Modem
PC
Figure 8: G.lite requires the connection of bridged taps, or
laterals from the main line for voice service, whereas G.DMT
isolates data from the voice service.
Data-Safe
Butt Set
Figure 9: Verifying voice service at outside facilities with the use
of an ADSL/POTS splitter and a data-safe butt set.
To receive more information or make suggestions regarding this document,
please contact Harris Technical Support at 1 (800) 437-2266.
— 13 —
Additional white papers available from Harris:
• Test Strategies For DSL Deployment
• Testing in the Unbundled Loop
• Advanced DSL Provisioning Strategies: Leveraging IVA
(Interactive Voice Access) in the ILEC-to-CLEC Local Loop
Hand-Off
© 2000 Harris Corporation, All Rights Reserved
All trademarks or registered trademarks used herein belong to their respective owners.
Specifications subject to change without notice.
Communications Products Division | 809 Calle Plano | Camarillo, California 93012-8519 USA
www.harris.com 1-800-437-2266
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Printed in USA, Form No. 3380 06/00/10M