Download FTTx PON Guide Testing Passive Optical Networks

FTTx PON Guide
Testing Passive Optical Networks
Fourth
Edition
This pocket guide provides an introduction to FTTH technology and testing during installation,
activation and troubleshooting of passive optical networks (PONs).
From POTS to PONs
The invention of the telephone in 1876 and the founding of the Bell Telephone Company in 1878 set the
stage for the widespread development of what is now known as the plain old telephone system (POTS).
Two years later, a photophone, as it was called, allowed for the transmission of sound over a beam of light.
Over the years, various pioneers have made a long series of fascinating discoveries and technological
breakthroughs, including the laser and the singlemode optical fiber, that make it possible to transmit
massive amounts of information over long distances using light. Today, more than 90% of US longdistance traffic is carried over optical fibers. However, twisted pairs of copper wire are still widely used
for the short-distance connections between the central office (CO) and subscribers.
Fiber-to-the-home (FTTH) technology represents an attractive solution for providing high bandwidth from
the CO to residences and to small- and medium-sized businesses. FTTH is cost-effective because it
uses a passive optical network (PON).
What makes FTTH even more interesting is the increased network reliability and ease of network testing,
measuring and monitoring. These systems follow the same basic principles as standard fiber networks,
enabling the use of much of the same gear for installation and maintenance.
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Acknowledgements
This guide would not have been possible without the enthusiasm and teamwork of EXFO staff, particularly the hard
work and technical expertise of the Product Line Management team and Dr. André Girard, Senior Member of Technical
Staff, who also plays a prominent role in the following international organizations:
•
•
•
•
•
Member of ITU-T SG15 on Optical and Other Transport Technologies
International Convenor of IEC SC86B WG7 on Passive Components
Chairman of Canada IEC TC86 National Committee
Co-Chair of TIA SC FO-4.3 (Interconnecting Devices and Passive Components)
Canada Liaison to ANSI IEC Technical Advisory Group
No part of this guide may be reproduced in any form
or by any means without the prior written permission of EXFO.
Printed and bound in Canada
ISBN 1-55342-002-0
Legal Deposit—National Library of Canada 2004
Legal Deposit—National Library of Quebec 2004
© 2009 EXFO Electro-Optical Engineering Inc., Quebec City, Canada. All Rights Reserved.
FTTx PON Guide: Testing Passive Optical Networks, 4th edition
Table of Contents
1. Introduction to FTTx ................................................................................2
4. PON Installation Testing ..............................................................30
Description................................................................................................................3
Why FTTx is Hot ..................................................................................................7
Types of PONs ......................................................................................................9
Available Services ..........................................................................................12
Connector Inspection and Maintenance ......................................31
Performing the Tests........................................................................................34
Test Setup for ORL and Optical Loss Measurment............35
Test 1: ORL Testing........................................................................................37
4.4.1 ORL Testing Using an ORL Meter or an OLTS ......38
4.4.2 Procedure Using an ORL Meter or an OLTS............39
4.4.3 ORL Testing Using an OTDR ................................................40
4.4.4 ORL Measurement Procedure Using an OTDR ........40
4.5 Test 2: Bidirectional Loss Testing ......................................................42
4.5.1 Loss Testing Using an OPM and an OLTS ................44
4.5.2 Loss Measurement Procedure Using an OLTS ......46
4.5.3 Loss Measurement Using an OTDR ................................47
4.6 OTDR Settings ....................................................................................................52
4.6.1 Procedure ................................................................................................53
5. Service Activation Testing ........................................................56
5.1 OLT (Initial Service Activation only)..................................................57
5.2 Optical Network Terminals (ONTs) ..................................................58
5.3 Multiple Testing Locations........................................................................58
5.4 Storing Data during Service Activation ........................................59
1.1
1.2
1.3
1.4
2. Network Design and Engineering ..............................14
2.1 Typical FTTx Architecture ..........................................................................14
2.1.1 Collision Avoidance in Upstream Transmissions..........17
2.2 FTTx Equipment ................................................................................................17
2.2.1 Description ............................................................................................17
2.2.2 Splitters ....................................................................................................21
2.3 Active Equipment ............................................................................................22
3. PON Installation ..........................................................................................24
3.1 OSP PON Installation ..................................................................................24
3.1.1 OSP Fiber................................................................................................24
3.1.2 OSP Splitters, Patch Panels and Fiber Management......25
3.1.3 OSP Splices ..........................................................................................25
3.1.4 OSP Drop Terminals ......................................................................25
3.2 MDU Installation ................................................................................................26
3.2.1 The Fiber Distribution Hub (FDH) ......................................26
3.2.2 The Riser Cables ..............................................................................26
3.2.3 The Fiber Collector (FC) ............................................................28
3.2.4 The Fiber Distribution Terminal (FDT)..............................28
3.2.5 The Drop Cable ..................................................................................28
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4.1
4.2
4.3
4.4
6. Network Troubleshooting ..........................................................62
7. Abbreviations and Acronyms ..............................................70
8. List of ITU-T PON Recommendations ..................74
9. Appendix ..................................................................................................................77
FTTx PON Guide
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1. Introduction to FTTx
1. Introduction to FTTx
1.1 Description
Singlemode optical fiber, with its almost unlimited bandwidth, is now the transport medium of choice in long-haul and
metropolitan networks. The use of fiber-optic cable—rather than copper cable—significantly reduces equipment and
maintenance costs, while dramatically increasing quality of service (QoS), and now more than ever, many corporate
customers have access to point-to-point (P2P) fiber-optic services.
Fiber-optic cables are now deployed in the last mile, the segment of the network that extends from the central office
(CO) to the subscriber. Since this segment has typically been copper-based, the high-speed services available
to residential customers and small businesses have been limited to generic digital subscriber lines (xDSL) and hybrid
fiber-coaxial transmissions (HFC). The main alternative—wireless transmission with direct broadcast service (DBS)—
requires an antenna and a transceiver. Therefore, copper- and wireless-based transport present the following shortcomings:
• Limited bandwidth in a context where there is an explosive growth in demand for more bandwidth and higher-speed
services over longer reaches
• Different media and equipment requiring extensive maintenance
Although fiber-optic cables overcome all of these limitations, one of the obstacles to providing fiber-optic services
directly to residences and small businesses has been the high cost of connecting each subscriber to the CO. A high
number of P2P connections would require numerous active components and a great deal of fiber-optic cables and
therefore, would have prohibitive installation and maintenance costs. An alternative presently being considered is
deployment of an entirely passive point-to-multipoint (P2MP) topology up to the building, while potentially keeping
copper and wireless premises networks or even providing the fiber up to the subscribers.
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FTTx PON Guide
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The FTTx (fiber-to-the-building, fiber-to-thehome, fiber-to-the-node, fiber-to-the-premises,
ONT
fiber-to-the-multidwelling-unit, etc.) architecture
offers an attractive solution. With FTTx,
ONT
ONT
ONT
a P2MP passive optical network (PON)
Residential
enables several customers to share the same
Splitter
connection, without any active components
Splitter
OLT
ONT
(i.e., components that generate or transform
Splitter
OLT
ONT
light
through
optical-electrical-optical
Splitter
OLT
Splitter
conversion) between the CO and customer
Optical
premises. A feeder fiber F1 is brought from an
ONT
Video
ONT
Transmitter
ONT
optical line terminal (OLT) in the CO to a fiber
Splitter
distribution hub (FDH) near a group of
ONT
ONT
premises (see Figure 1-1(a)). In the FDH, a
ONT
Splitter
passive optical splitter is used to typically
connect a number of F2 FD fibers to the same Figure 1-1(a). Providing triple-play services over a high-bandwidth passive optical network
feeder fiber. Then, each customer premises is
provided with an optical network terminal (ONT) connected on one side to the F2 and on the other side to the premises
network. This P2P architecture dramatically reduces costs of network installation, management and maintenance.
WDM
Coupler
WDM
Coupler
WDM
Coupler
4 FTTx PON Guide EXFO
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The OLT provides voice and data downstream
transmission using a 1490 nm wavelength
band, while the ONT provides upstream
transmission with a 1310 nm wavelength
band, allowing non-interfering bidirectional
transmission on the same fiber. In addition, the
OLT may be connected to one branch of a 2x1
wavelength-division multiplexing (WDM)
coupler, while the second branch is connected
to a video transmission system. The video
is provided downstream only, usually in a 1550 nm
wavelength band; once over, the video signal,
if it is available, can then be transmitted over
the same 1490 nm band as for voice
and data.
FDT
FDH: Fiber distribution hub
FTT: Fiber distribution terminal
ONT: Optical network terminal
ONT
ONT
FDH
WDM
Coupler
OLT
WDM
Coupler
OLT
F1
WDM
Coupler
OLT
Optical
Video
Transmitter
Figure 1-1(b). Providing triple-play services over a high-bandwidth PON
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Variance of the architecture consists of connecting a number of F2s to a drop terminal and then to an F3 drop fiber to
the premises (FTTP). Various shared bandwidths will be provided, depending on customer requirements. So far, typical
symmetric or asymmetric rates of 155 Mbit/s, 622 Mbit/s, 1.5 Gbit/s and 2.5 Gbit/s have been planned. The protocol
of choice is based on the asynchronous transfer mode (ATM) and is typically called Ethernet for EPON; ATM-PON for
BPON; ATM and GEM (TDM and Ethernet) for GPON upstream; ATM, GEM (TDM and Ethernet) and ATM/GEM for
GPON downstream.
There are many variations of the FTTx architecture
(see Figure 1-2), including:
FTTC
WDM
Coupler
ONT
ONT
• Fiber-to-the-cabinet (FTTCab)
• Fiber-to-the-curb (FTTC)
OLT
• Fiber-to-the-home (FTTH)
FTTH
ONT
ONT
• Fiber-to-the-node (FTTN)
• Fiber-to-the-premises (FTTP)
= Fiber
= Copper
Figure 1-2. Typical FTTx network
• Fiber-to-the-office (FTTO)
• Fiber-to-the-user (FTTU)
• Fiber-to-the-multidwelling-unit (FTT-MDU)
6 FTTx PON Guide EXFO
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1.2 Why FTTx is Hot
In 1995, British Telecom, Bell South, Bell Canada, NTT and five other international telecommunications companies met
to form the Full-Service Access Network (FSAN), which was founded to facilitate the development of suitable accessnetwork-equipment system specifications.
The United States legislature adopted the Telecommunications Act of 1996 to promote and reduce regulation in order
to secure lower prices and higher-quality services for American telecommunications consumers and to encourage the
rapid deployment of new telecommunications technology.
The International Telecommunications Union (ITU-T) turned FSAN specifications into recommendations. The FSAN
specification for ATM-based PONs became an international standard in 1998 and was adopted by the ITU as
recommendation G.983.1.
In 2001, the FTTH Council was formed to promote FTTH in North America and to advise the US legislature; this
resulted in the Broadband Internet Access Act of 2001, which provides tax incentives to companies that invest in nextgeneration broadband equipment.
In 2003, the US Federal Communication Commission (FCC) removed unbundling requirements on newly deployed
networks, such as FTTx (unbundling regional Bell-operating companies’ (RBOCs) obligation to allow competitive local
exchange carriers (CLECs) to use their network), making the technology more attractive to major carriers. This means
that RBOCs can invest in last-mile fiber network—without having to share it with competitors−providing a major incentive
toward the deployment of FTTx networks. Some predict a US$1 billion market for FTTx networks, for RBOCs alone.
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As a result of these developments, interest in FTTx has spurred:
• FTTx offers the high-bandwidth capability of optical fibers and a wide diversity of services (e.g., data, POTS and video)
at a low cost since a number of end-users can share bandwidth on a single fiber and also that all outside plant
equipment is passive
• New standards such as those established by the ITU-T, the IEC and the Institute of Electronic and Electrical
Engineers (IEEE) have greatly increased the design commonality, survivability and security of PONs, opening the
opportunity for economies of scale and lower costs that previously were not conceivable
• FTTx can now be offered by many different types of carriers:
— Incumbent local exchange carriers (ILECs) and regional Bell-operating companies (RBOCs)
— Rural local exchange carriers (RLECs)
— Competitive local exchange carriers (CLECs)
— Utility companies
— Municipalities
— Etc.
PON deployments are happening worldwide and the most active countries include China, Japan and the United States.
8 FTTx PON Guide EXFO
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1.3 Types of PONs
As shown in Table 1-1, there are a number of different technologies available for PONs. Next-generation (NG) PONs,
such as WDM-PON and 10G PON, are currently being studied by standard committees.
Type
BPON (Broadband PON)
Standard
ITU-T G..983 series
Protocol
ATM
Services
Voice/data/video
Maxim um Physical
distance (OLT to ONT)
km
20
Split ration
Up to 32
Downstream OLT Tx
Nominal bit rate
Mbit/s
155.52
622.08
Upstream ONU Tx
1244.16
155.52
622.08
1260-1360
(MLM1, SLM)
Operating
Wavelengths band
nm
ORLMAX
dB
1480-1580
1480-1500
1260-1360
1280-1350 (MLM2)
1288-1338 (MLM3)
>32
Table 1-1. Available PON architectures
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FTTx PON Guide
EXFO 9
GPON (Gigabit-Capable PON)
Type
GPON
GPON-ERG
G.984 series
Standard
EPON (Ethernet PON)
G.984.6
IEEE 802.3ah
Protocol
Ethernet, TDM, TDMA
Ethernet
Services
- Voice/data
- Triple play
- File exchange/distant learning/tele-medecine/IPTV/video on demand
Triple play
Maxim um Physical
distance (OLT to ONT)
Split ration
Nominal bit rate
Operating
Wavelengths band
ORLMAX
20
Up to 60 (ODN distance)
1000BASE-PX10: 10
1000BASE-PX20: 20
up to 64
16.32 or 64
(restricted by path loss)
1x16
1x32 (with FEC or DFB / APD)
km
Mbit/s
nm
Downstream
Upstream
Downstream
Upstream
Downstream
Upstream
1244.16 / 2488.32
155.52/ 622.08/
1244.16
2488.32
1244.16
1000
1000
1480-1500
(Basic band)
OEO (ONU EXT):
1260-1360
-1480-1500
-1550-1560
(Enhancement band for video)
dB
1260-1360
Possibility of using
shorter C-band
wavelengths
downstream and
1550 nm upstream
1550-1560
(Enhancement
band- for video
distribution
>32
OEO (OLT EXT):
1290-1330
OA:
1300-1320
(OBF)
100BASE-PX10:
Downstream:
1490 nm + PIN Rx
Upstream: 1300 nm
(low-cost FP optics + PIN Rx)
100BASE-PX20:
Downstream: 1490 nm + APD Rx
Upstream:1300nm
(DFB optics + PIN Rx)
15
Table 1-1. Available PON architectures (continued)
TDM
TDMA
OBF
Time division multiplexing
Time division multiplexing access
Optical band pass filter
10 FTTx PON Guide EXFO
ONU
ODN
ERG
Optical network unit (optical network terminal
(ONT), when connected to home network)
Optical distribution network
Extended range GPON
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Type
GPON
ITU-T G.984.1
Standard
Optical distribution
network class (ODN)
A
B
C
A
B
Ca
IBP e
C+
A
B
C
A
Nom inal bit rate
1244.16
B
C
A
B
C
Upstream b
Downstream
2488.32
155.52
622.08
1244.16
<Plaunch >Min
dBm
–4
+1
+5
0
+5
+3
+ 1.5
+3
–6
–4
–2
–6
–1
–1
–3c
–2
<Plaunch >Max
dBm
+1
+6
+9
+4
+9
+7
+5
+7
0
+2
+4
–1
+4
+4
+2c
+3
+7
Sensitivity Min
dBm
– 25
– 25
– 26
– 21
– 21
– 28
– 28
– 32
– 27
– 30
– 33
– 27
– 27
– 32
– 24 d
– 28
– 29
Overload Min
dBm
–4
–4
–4
–1
–1
–8
–8
– 12
–5
–8
– 11
–6
–6
– 11
–3d
–7
–8
+2
Table 1-2. GPON/BPON ODN class
Notes
a. The values assume using high power DFB laser for OLT Tx and APD in ONU Rx. DFB laser + SOA, or HP LD used in OLT in future will PIN in ONU Rx.
b. Does not include power leveling.
c. MLM lasers not supporting the full ODN fibre distance can be used if the Max Tx-Rx ODN fibre distance is restricted to 10 km. MLM laser types
can be used to support this distance at 1244.16 Mbit/s.
d. The values assume the use of OLT PIN Rx for Class A. Depending on the number of connected ONUs, OLT APD Rx could be used, allowing
less expensive ONU Tx.
e. Industry best practice.
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FTTx PON Guide
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Type
BPON
ITU-T G.983 series
Standard
Optical distribution
network class (ODN)
B
C
A
B
C
A
B
C
B
C
Downstream
Nominal bit rate
155.52
A
B
C
Upstream
622.08
1244.16
155.52
622.08
<P launch>Min
dBm
–4
–2
–7
–2
–2
–4
+1
+5
–4
–2
–6
–1
–1
<P launch>Max
dBm
+2
+4
–1
+4
+4
+1
+6
+9
+2
+4
–1
+4
+4
Sensitivity Min
dBm
– 30
– 33
– 28
– 28
– 33
– 25
– 25
– 26
– 30
– 33
– 27
– 27
– 32
Overload Min
dBm
–8
– 11
–6
–6
– 11
–4
–4
–4
–8
– 11
–6
–6
– 11
Table 1-2. GPON/BPON ODN class (continued)
CO
1.4 Available Services
Figure 1-3 shows the wavelengths
and services used in an FTTx network.
Splitter 1 x N
ONT
OLT
Optical
Video
Transmitter
WDM
Coupler
ONT
EDFA
1490 nm Voice and data
1550 nm Overlaid analog RF video
(may not be provided)
1310 nm Voice and data
Figure 1-3. Wavelengths and services in an FTTx network
12 FTTx PON Guide EXFO
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2. Network Design and Engineering
2. Network Design and Engineering
2.1 Typical FTTx Architecture
Figure 2-1 illustrates the general
architecture of a typical FTTx
network. At the CO, also referred to
as the head-end, the publicswitched
telephone
network
(PSTN) and Internet services are
interfaced with the optical
distribution network (ODN) via
the optical line terminal (OLT).
The downstream 1490 nm and
upstream 1310 nm wavelengths
are used to transmit data and voice.
Analog RF video services are
converted to optical format at the
1550 nm wavelength by the optical
video transmitter. The 1550 nm
and 1490 nm wavelengths are
combined by the WDM coupler and
transmitted downstream together.
At present, there are no standards
published for upstream video
transmission. IPTV is now transmitted
over 1490 nm.
14 FTTx PON Guide EXFO
CO
1490/1550 nm
PSTN
Class 5 Switch
T1-DS-3 TDM
WDM
Coupler
Internet
OC-3/OC-12
OLT
ATM/Ethernet
1P Switch
Video
storage
VOD
Server
Splitter
1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
32
ONT
POTS
Twisted-pair
ONT 10/100-Base-T
Ethernet
Data
EDFA
Digital
Video
RF Modulators
Optical
Video
Transmitter
Optical
Video
Coax
cable
Setup
box
broadcast
TV
Analog
Digital
Video
RF Modulators
Local TV
Broadcast
Signals
Residence
1310 nm
Satellite RF Modulators
TV Signals
Figure 2-1. FTTx general architecture
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In summary, the three wavelengths (1310,
1490 and 1550 nm) simultaneously carry
different information and in various directions
over the same fiber.
The F1 feeder cable carries the optical
signals between the CO and the splitter,
which enables a number of ONTs to be
connected to the same feeder fiber. An ONT
is required for each subscriber and provides
connections for the different services (voice,
data and video). Since one FTTx network
typically provides service to up to 32
subscribers, more than 64 with GPON, many
such networks, originating from the same CO,
are usually required in order to serve
a community.
There are different architectures for
connecting subscribers to the PON. The
simplest uses a single splitter (see Figure 2-2),
but multiple splitters can also be used (see
Figure 2-3).
CO
OLT
FDH
ONT
..
.
1x32 ...
..
.
Splitter
WDM
Coupler
Optical
Video
Transmitter
ONT
Figure 2-2. Single splitter FTTx network
Neighborhood FDH
CO
OLT
Optical
Video
Transmitter
FDH
WDM
Coupler
1x4
1x8
..
..
..
..
.
ONT
..
..
..
..
.
..
..
..
..
Splitter
1x8
..
..
..
..
.
ONT
ONT
ONT
Figure 2-3. FTTx network with multiple splitters
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FTTx PON Guide
EXFO 15
ONU1
ONU2
VDSL
FTTC
VDSL
ONU3
OLT
OLT
CO
ONU4
ONU
FTTB
ONU5
ONU1
ONT
Splitter
ONU5
OLT
PON
ONU2
ONU
FTTH
ONU2
ONT
ONU4
VDSL
FTTC
ONU3
OLT
ONU
Splitter
ONU1
ONU3
VDSL
ONU4
ONU5
Figure 2-4. PON topologies
FTTH ONT
Figure 2-5. FTTH, FTTB and FTTC
In addition, as shown in Figure 2-4, other topologies such as the star, ring and bus topologies also exist; even protection
is anticipated with different strategies.
In some cases, it may not be necessary to bring the fiber directly to every subscriber. In this case, the fiber from the
splitter is brought to an ONT, and short copper-based links (typically VDSL, which provides sufficient bandwidth for
triple-play services over short distances) are used for the final connection (see Figure 2-5); this is also known as fiberto-the-building (FTTB). A single PON can use a combination of FTTH, FTTB and other types of connections.
WDM couplers are used to multiplex the downstream voice/data signal at 1490 nm with the downstream RF video
signal at 1550 nm and the upstream voice/data signal at 1310 nm.
16 FTTx PON Guide EXFO
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2.1.1 Collision Avoidance in Upstream Transmissions
In the case of the upstream direction (i.e., toward the OLT) of a P2MP PON, collisions of data must be prevented from
different ONT signals arriving at the splitter at the same time; therefore, time-division multiple access (TDMA) is used.
TDMA can send burst or delayed data from each ONT back to the OLT at a specific time (timeslot). Each ONT
transmission timeslot is granted by the OLT so that the packets from various ONTs do not collide with each other.
2.2 FTTx Equipment
2.2.1 Description
PON equipment consists of gear and components located between the OLT and the customer premises (the ONT);
this includes both optical and non-optical components of the network. The optical components make up the optical
distribution network (ODN) and include splices, connectors, splitters, WDM couplers, fiber-optic cables, patchcords and
possibly drop terminals with drop cables. The non-optical components include pedestals, cabinets, patch panels, splice
closures and miscellaneous hardware (see Figure 2-6).
CO
Voice
Data
FDH
Drop Terminal
Drop
Splitter
1XN
WDM
Coupler
ONT
Distribution Fiber
ONT
OLT
ONT
Optical
Video
Transmitter
EDFA
Patch Panel
Patch Panel
Drop Terminal
ONT
Figure 2-6. FTTx equipment for ONU installed outside premises
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FTTx PON Guide
EXFO 17
Outside plant (OSP) equipment includes the following:
1260
1360
O
1675
1460
E
U
• Fiber-optic cables: the feeder cables form the segment between
the CO and the first splitter; distribution fibers link the splitter to
the drop terminals (if used) near the subscribers and drop cables
(if also used) connect the individual ONTs to the drop terminal
Note: On account of Rayleigh scattering, macrobending,
microbending, etc., fiber-optic cables introduce signal loss
(attenuation) that is proportional to their length. Figure 2-7
shows the attenuation in a typical fiber.
• Fiber distribution hub(s) include:
O = Original band S = Short band
L = Long band
E = Extended band C = Conventional band U = Ultra-long band
Note
= Low wate r-peak fiber
- Cabinets, pedestals, splice enclosures (aerial or buried)
- Splitter(s) (an important component; see section 2.2.2)
- Patch panel(s)
- Fiber-management elements
Figure 2-7. Spectral attenuation
• Drop terminals
• Connectors: Most often, but not exclusively, SC/APC is used
(8° slope on ferrule reduces reflections by more than 60 dB,
typical loss ≤ 0.5 dB)
18 FTTx PON Guide EXFO
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In-building (MDU) equipment includes the following:
Depending on the type of MDU to be deploy (see Figure 2-8 (a) and (b)), the equipment used can be similar to the
equipment used in OSP deployments (see Figure 2-8 (b)) or specially designed for indoor use (see Figure 2-8 (a)).
Indoor equipment is less subject to ash environment and therefore do not require the same ruggedness as the OSP
equipment. The following items will generally be found in indoor deployments:
• Fiber-optic cables:
- The feeder cables form the segment between the CO and the
fiber distribution hub (FDH) generally located in the basement
of the building.
- The riser cables form the segment between the FDH and the
fiber distribution terminal (FDT) located on each floor or the
fiber collector (FC). Riser cables can be composed of one
single fiber per splitter port or MTP cables.
- The drop cables form the segment between the FDT and the
ONT located at the apartment. It is generally made of bend
insensitive fiber.
• Fiber distribution hub(s) (FDH) include:
FDT
FDT
FC
FDT
FC
FDT
FDH
FDH
- Cabinets, splice enclosures
To CO
- Splitter(s) (an important component; see section 2.2.2)
- Patch panel(s)
Figure 2-8 (a). High/medium-rise MDU equipment
- Fiber-management elements
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FTTx PON Guide
EXFO 19
• Fiber distribution terminal (FDT):
- The FDT—located on each floor—serves as the junction between the FDH and the drop cable; it can be
connectorized or spliced.
• Fiber collector (FC):
Outdoor ONT
- The FC serves as a junction
point between the FDH and
few FDTs (see Figure 2-8 (a)).
Outdoor FDT
Indoor ONT
Outdoor FDH
Feeder Cable F1
Figure 2-8 (b). Horizontal/garding style MDU equipment
20 FTTx PON Guide EXFO
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2.2.2 Splitters
Number of Ports
Splitter Loss (dB)
The bidirectional optical branching device used in the P2MP PON is called an
(excluding connectors
“optical power splitter” or simply a “splitter”, which has one input from the F1 port
and excess
and multiple output ports. Splitters are passive because they require no external
splitter loss)
energy source other than the incident light beam. They are broadband and only
2
3
add loss, mostly due to the fact that they divide the input (downstream) power.
4
6
This loss, called “splitter loss” or “splitting ratio”, is usually expressed in dB and
depends mainly on the number of output ports, as shown in Table 2-1. For
8
9
instance, the input (downstream) optical signal is divided equally in cascade or
16
12
branches; for instance a 1x2 splitter has only two branches or one split that
32
15
bares a 3 dB loss (50% light in each leg). In a 1x4 splitter, another two branches
64
18
will be added to each leg of the original 1x2−split this time adding another 3
dB for a total of 6 dB loss. In a 1x8 splitter, two more branches or 1x2 split will Table 2-1. Splitter loss
be added to each leg of the original 1x4 split, again adding another 3 dB for a
total of 9 dB loss. A 1x16 splitter will then bare a 12 dB, and a 1x32 splitter will
have a minimum of 15 dB loss, not counting any additional loss due to connections and imperfections (typically 1dB is added
to the original splitting loss) therefore, a 1x32 splitter will have a typical 16 dB loss.
PON uses an equal part among the output ports to F2, allowing multiple users to share a single optical fiber and consequently
a shared bandwidth. In the upstream direction, optical signals are combined from a number of ONTs into the single fiber F1.
It should be noted that, contrary to what one might expect, the splitter adds approximately the same loss−even for light
traveling in the upstream direction.
There may be one splitter or several cascaded splitters in an FTTx network, depending on the network topology. ITU-T
Recommendation G.983 currently enables split ratios up to 32, while Recommendation G.984 extends the ratio up to 64.
Regardless of the topology, the splitter must accommodate the allowed optical-loss budget.
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FTTx PON Guide
EXFO 21
Splitters can be packaged in different shapes and sizes, depending on the basic technology used. The most
common types are the planar waveguide (typically for high split ratios) and the fused-biconic taper (FBT) fiber
(typically for low counts). Both types are manufactured for mounting in closure tray assemblies. Figures 2-9 and
2-10 illustrate the two technologies.
PON Passive Optical Components
PON Passive Optical Components
Splitter Technology
Splitter Technology
Planar Waveguide
Fused Biconic Taper (FBT) Fiber
Core
Cladding
Si Substrate
Mask
Core
Cladding
Si Substrate
Core
Cladding
Si Substrate
2
Input
PLC = Planar Lightwave Circuit
Optical circuit on a substrate made using
tools and techniques based on CVD or Icon
Exchange based on semiconductor industry
Fused Biconic Taper
Output
b = kn
3
1
Cladding
Core
Cladding
Si Substrate
Figure 2-9. Planar waveguide splitter
Figure 2-10. FBT splitter
2.3 Active Equipment
The active equipment includes the following:
• The OLT (voice/data transmitter/receiver) located at the CO
• Video equipment (transmitter) and an erbium-doped fiber amplifier (EDFA), which is used to amplify the
analog RF video overload signal before transmission through the WDM coupler
• The ONT (its electrical power supply and battery backup) located at the customer premises
22 FTTx PON Guide EXFO
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3. PON Installation
3. PON Installation
Installation of PON equipment in an FTTx network can be carried out in many ways and each installation may be
different, depending on such factors as the distance from the CO, residential density and distribution urbanism, to name
a few. Fiber-optic cables can be installed using the most appropriate aerial- or underground-installation techniques. The
placement of splitters and other passive components and the types of cabinets used depend on geographical factors
and on the PON topology.
3.1 OSP PON Installation
3.1.1 OSP Fiber
Fiber-optic cable installation is one of the most costly elements in PON deployment. Several methods are available, and
the choice of method depends on various factors, including cost, right-of-way, local codes, aesthetics, etc., and on whether
the installation is being performed in a new premises development (Greenfield installation) or in an existing development
over existing routes (overlay/overbuild). Three basic cable-installation methods are available:
• The direct burial method places the cable underground in direct contact with the soil; this is done by trenching,
plowing or boring.
• A duct installation in which the optical cable is placed inside an underground duct network. Although the initial duct
installation is more expensive than a direct burial installation, the use of ducts makes it much easier to add or remove cables.
• Aerial installations comprise the placement of the cable on poles or towers above the ground. This type of installation,
commonly used for overbuilding, is usually more affordable than underground installation and does not require heavy
machinery. The optical cable can be lashed to a supporting messenger cable or self-supporting optical cables can be used.
For densely populated areas with particular right-of-way challenges, several alternative methods are available such
as installing the cable in grooves cut into the pavement or inside drainpipes, sewer pipes and natural gas pipelines.
Also, there are three types of cables: feeder F1, distribution F2 and drop F3 (optional).
24 FTTx PON Guide EXFO
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3.1.2 OSP Splitters, Patch Panels and Fiber Management
Splitters and patch panels are usually installed in cabinets mounted on pedestals or fixed on posts, also called “fiber
distribution hubs” (FDHs). The number, type and placement of the splitters depend on the topology of the network and
the number of fibers in the F1 feeder cable (see FTTx Equipment, Figure 2-6).
3.1.3 OSP Splices
Splices can be mechanical or fused. Mechanical splices are the least expensive but have higher insertion loss and
backreflections than fused splices, which have very low loss (0.02 dB) and almost no backreflection but typically require
expensive and extensive fusion-splicing equipment and a well-trained technician. The number of splices depends on
the cable section lengths used (typical section lengths are ≤ 2 km, 4 km and 6 km). The shorter the length, the easier
the maintenance, but the whole cable assembly requires more splices, time and costs much more than longer lengths,
which in turn are difficult to maintain. Note that splices are protected from the environment by splice closures.
3.1.4 OSP Drop Terminals
Drop terminals are typically used for easing service connection and distribution and, if used, can be aerial, underground
or located in apartment buildings, depending on the installation. Cable drops between splitter and premises are
sometimes pre-connectorized and can be buried or aerial-mounted. They are usually short in length (≤ 30 m).
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FTTx PON Guide
EXFO 25
3.2 MDU Installation
3.2.1 The Fiber Distribution Hub (FDH)
The FHD is generally installed in the basement of the building and acts as the
demarcation point between the outside network and the in-building network. In some
cases, where the number of floors is high like in high-rise building, additional FDHs
can be added on the top floors. FDHs are available in a range of sizes: 72, 144, 216,
etc. and are designed for front access via a swing frame configuration so that they can
be mounted on a wall, rack or pedestal.
FDT
FDT
FC
FDT
FDH
F1
To CO
3.2.2 The Riser Cables
As explained in section 2.2.1, riser cables can be
composed of individual fibers going from each port of the
splitter (located in the FDH) to each port of the FDTs or
they can be composed of an MTP cable going from the
FDH to the fiber collector (FC). Typically in high-rise
buildings, a straight stack riser system with multiple
sleeves is available and can be used as channels for the
riser cables.
FDT
FDT
FC
FDT
FDH
F1
To CO
Figure 3-1. Fiber distribution hub
installation in MDU
The riser cables can be deployed in the building by using fusion-spliced terminations or
a plug and play (pre-engineered) system approach. A pre-engineered solution implies
that cables arrive with a pre-defined length and the terminations are done with
a connector instead of fusion splice. Due to the simplicity of deployment, this solution
becomes attractive in Brownfield—where deployment speed is critical.
Figure 3-2. Riser cable installation
in MDU
26 FTTx PON Guide EXFO
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Traditional Fusion-Splice Terminations
Spooled Pre-Terminated Components
Positive Factors
Positive Factors
• Once the splices have been well performed, the network design is very stable
• More attractive for Brownfield situations
• Less connectors in the design, especially at intermediate points between the FDH
patch panel and the ONT connector; therefore less chance of contamination
or dirt accumulation—especially before construction has been completed
• Attractive proposition for situation where splicing crew is more
expensive or hard to get
• Increase the speed deployment of the project (less splicing time)
• Decrease the cost of the labor in the project (less splicing fees)
• Lower cost of components
• Allow additional test connection points between the FDH patch panel and
the connector at the ONT
Negative Factors
Negative Factors
• If splicing fees are expensive or splicing labor is hard to get for a particular
project, this approach may be an issue
• Many connectors in the design, in addition to at the FDH patch panel location,
can create dirt accumulation—especially before construction has been completed
• Does not provide intermediate test access
point between the FDH patch panel and the ONT connector
• Increase in the cost of components
General Appreciation
• De-facto approach: contractors are used to splice and the presence of connectors
in non-hardened cabinet, especially when construction is not finished, can
create a situation where the connector becomes contaminated and major
cleaning or re-connectorization is required at some places
General Appreciation
• This approach is obligated to provide evidence for its position. This is what the
vendors are working on now and customers are listening. Interviewees have
been open-minded and some have said that this approach must generate
savings >20-30% to justify the use of this type of component
Table 3-1. MDU riser cable deployment approaches (highlights)
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FTTx PON Guide
EXFO 27
3.2.3 The Fiber Collector (FC)
As explained in section 2.2.1, the fiber collector (or collector enclosure) serves as
a junction point between the FDH and few FDTs. It is mainly used when the MTP
approach is selected to deploy the riser cables. They are generally mounted on walls
in a central location where they are easily accessible.
FDT
FDT
3.2.4 The Fiber Distribution Terminal (FDT)
As explained in section 2.2.1, the fiber distribution terminal is installed on every level
of the building. In the case of the connectorized MDU solution, the FDTs need to be installed
in accessible locations for maintenance purposes (e.g., connector cleaning). In the case
of a spliced approach, where all the riser and drop cables are spliced together, ease
of accessibility is less of a concern.
FC
FDT
FDH
F1
To CO
Figure 3-3. Fiber collector in MDU
3.2.5 The Drop Cable
Horizontal drop cables reach every living unit, where the ONT stands (see Figure 3.1). The drop
cable is generally be made of a bend-insensitive fiber that will facilitate their deployment.
Figure 3-4. Structure wiring box (SWB) with
ONT and battery back-up. (Pictures courtesy
of Connexion Technologies)
28 FTTx PON Guide EXFO
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4. PON Installation Testing
4. PON Installation Testing
The purpose of any fiber-optic network is to perform high-speed, errorfree data transmission. Adequate testing during network installation
guarantees that products meet specifications, plus it minimizes costly
and time-consuming troubleshooting efforts by locating dirty/damaged
connectors, questionable splices and other faulty components before
they disrupt service.
One of the most important factors in ensuring proper transmission
is controlling the power losses in the network against the link loss
budget specifications from the ITU-T Recommendation and IEEE
standard, which is done by establishing a total end-to-end loss budget
with sufficient margin, while reducing backreflections to a minimum.
This is particularly true for high-power analog RF video signals from
extremely narrowband lasers, since strong backreflections degrade the
quality of the video transmission.
Figure 4-1. Adequate loss and backreflection testing
is important
Adequate loss and backreflection testing is important to ensure that at each transmission wavelength:
• End-to-end loss and backreflection meet the specifications
• Upon questionable results, each segment meets or exceeds the requirements
Note: The ratio of the output power to the input power of a device is called the “attenuation” and has a positive value
because the loss is increasing. When a device is inserted in an assembly, the attenuation is called the
“insertion loss” and has a negative value because the performance is decreased.
30 FTTx PON Guide EXFO
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4.1 Connector Inspection and Maintenance
Connectors are key components that interconnect the entire network elements, which is why maintaining them in good
condition is essential to ensure that all the equipment operates to their maximum performance—to avoid catastrophic
network failure.
Due to the high power levels involved, it is especially important that all connectors be properly inspected and cleaned—
meeting loss budget and specifications. As singlemode fibers have very small cores, typically 9 micrometers in diameter
(see Figure 4-2), a single particle of dust or dirt can obstruct the transmission area; therefore, when making
connections, observe the following guidelines:
• Never allow unmated connectors to touch any surface and never touch a connector ferrule for any reason other than cleaning
• First, inspect the connector endface, if it is not clean, clean
it and inspect it again using
a fiberscope or a videoscope
(which is safer and more
accurate) prior to mating—even if
there was only a temporary
disconnection. Clean and inspect
the test equipment connectors
every time the instrument is used
and use a fiberscope or
videoscope after cleaning
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Buffer Coating
(~250 to 900 µm)
Zone B: Cladding
(125 µm singlemode fiber)
Connector
End-face
Zone A: Core
(~9 µm singlemode fiber)
Mechanical
Section
Figure 4-2: Zone defining the ferrule
FTTx PON Guide
EXFO 31
• Use an appropriate cleaning method: dry or wet/dry. Figure 4.3, illustrates the step-by-step inspection/cleaning
procedure that you can follow before a fiber is connected to another optical component. To perform the dry or wet/dry
cleaning, you may use the following items such as a tape (Cletop), surface-cleaning pad, specialized lint-free wipes,
isopropyl alcohol (IPA) or pre-saturated wipes (IPA wipers).
• Keep unused connector ports capped and all unused caps in a small resealable plastic bag. Note that a number
of installations use APC connectors, especially when high-powered overload analog RF video is used, and since they
are angled, special care should be taken when inspecting.
WARNING!
- Never look directly into a live fiber with the naked eye. Always use protective gear to inspect cable ends
and connectors or use videoscope.
- Carefully follow all safety procedures listed in each of the test instrument’s user guide.
- Never look directly into fibers, connectors or equipment apertures, unless you are absolutely sure that the
light source has been powered off.
- When using a fiberscope, always be absolutely sure that the light source has been powered off. If possible,
use a videoscope to inspect fiber ends and connectors.
- Do not power up any laser-transmitter equipment until you are certain that all work has been completed
on the transmission system and that all cabled fibers are properly cleaned and connected.
32 FTTx PON Guide EXFO
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For further information on
connector maintenance, refer
to the following article on our
website (www.EXFO.com):
Inspect
Connector Inspection and
Maintenance
Is the
connector
endface
damaged or
dirty?
http://documents.exfo.com/
appnotes/anote191-ang.pdf
Damaged
Replace the
connector if
the damages
are critical
No
Connect
Dirty
Clean it:
dry-wet
or hybrid
Inspect
No
Is the
connector
endface
clean?
Yes
Connect
Figure 4-3. Connector inspection and cleaning procedure
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FTTx PON Guide
EXFO 33
4.2 Performing the Tests
The four main optical tests to be performed during network installation are:
•
•
•
•
Unidirectional cable-section attenuation before splicing
Bidirectional optical return loss (ORL) measurement
Bidirectional end-to-end attenuation measurement
Bidirectional end-to-end link characterization
These tests are described in detail further. Each part describes the test
setup and the test installation. Useful test instruments include an ORL
meter, optical loss test set (OLTS) or a combination of both, in addition
to an optical time-domain reflectometer (OTDR).
Ideally, the PON should be tested after each segment has been installed.
Therefore, once each section of the cable fiber is installed, OTDR tests should
be performed. After installing a splitter, end-to-end tests should be performed
on the feeder fiber F1 between each splitter output port and the output port
of the OLT. When the drop terminals have been installed, tests should be
performed between each drop terminal output port and the patch panel of the
fiber distribution hub (distribution fiber F2). This test can also be carried out
between the drop terminal port and the patch panel of the OLT. This is
performed when the output of the splitter is not connectorized but spliced
directly to the distribution fiber. Finally, when the drop cable is installed, the link
can be tested between the drop cable ONU connector and the OLT output
port.
34 FTTx PON Guide EXFO
Figure 4-4. EXFO’s cleaning kit
Figure 4-5. FIP-400 video inspection probe
www.EXFO.com
4.3 Test Setup for ORL and Optical Loss Measurement Link
There are two main methods to test ORL. The first is by using a continuous wave (CW)
method: light source and optical power detector at the same end. CW equipment is called
“ORL meter” and could be directly integrated in an OLTS. The other method is based on
an OTDR. Since communication over the fiber is bidirectional, the ORL must be measured
in both directions. Using an ORL meter or compatible OLTS at each end of the link, the ORL
should be measured first in one direction, then in the opposite direction. Modern OLTS and
OTDR units are used for measuring both ORL and optical loss at the same time.
The optical-loss test requires a sequence of two
measurements. Two OLTS units are first
referenced together using their individual light
sources. Then, each OLTS sends a calibrated
power value from its light source over the section
under test to the other OLTS, which measures the
received power and calculates the loss.
Figure 4-6. EXFO’s FOT-930
MaxTester—a multifunction
handheld ORL/OLTS
www.EXFO.com
Figure 4-7. FasTest: one-touch, automated
measurements in 7 seconds
FTTx PON Guide
EXFO 35
The OTDR is placed at the ONT and is able to measure the optical-loss and
reflectance for each component of the network and the overall loss of the total
link. The ORL is then calculated. The OTDR could also be used to test from
the OLT to the ONT. Notice that after the splitter, the optical loss and the ORL
should not be directly considered due to two factors: All legs of the splitter will
generate backscattering if they all have a certain length of fiber and therefore
will not show the true loss after the splitter, all lights coming back will reduce
the actual loss of each leg. The ORL after the splitter will be attenuated by the
splitter and therefore should not be consider.
Connector Type Typical ORL (dB)
UPC
50-55
APC
65-70
Table 4-1. Typical connector ORLs
Note: A larger value indicates less reflection and
is therefore better
ITU-T recommendations G.983 and G.984 series allow a maximum ORL of 32 dB for a link. IEEE 802.3ah allows a minimum
of 20 dB and a maximum of 15 dB for EPON. Note: Never connect an APC connector to a PC or UPC connector.
Table 4-1 shows a typical ORL value for different types of connectors.
Note: Be careful not to confuse the acronyms OLTS (optical loss test set) and OLT (optical line terminal).
36 FTTx PON Guide EXFO
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4.4 Test 1: ORL Testing
ORL is defined as the ratio of reflected power to incident power and is measured at the input of a device under test
(DUT). ORL represents the sum of all the reflections through all the optical interfaces of the DUT; it is given in dB units
and is a positive number. Reflectance, on the other hand, is a negative number and is defined as the reflection from a
single optical interface, such as a transition from a fiber end (glass) to air.
Link ORL is made up of Rayleigh backscattering from the fiber core and the reflectance from all the interfaces found
along the link. ORL can be a problem in digital high-speed transmission systems but is particularly critical for analog
transmission, such as the 1550 nm CATV signals possibly used in FTTx systems (e.g., analog RF video in a PON). While
Rayleigh backscattering is intrinsic to the fiber and cannot be completely eliminated, reflectance is caused by different
network elements (mainly connectors and components) with air/glass or glass/glass interfaces and can always be
improved by special care or better designs. To optimize transmission quality, backreflection effects (e.g., light-source
signal interference or output power instability) must be kept to a minimum. Therefore, attention must be focused on
ensuring quality network connections through highly accurate ORL measurements.
The main effects of ORL include the following:
• Strong fluctuations in the laser output power
• Interference at the receiver end
• Lower carrier-to-noise ratio in analog systems, leading to distortions on video signals
• Higher bit error rate (BER) in digital systems
• Possible permanent damage to the laser if not protected
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4.4.1 ORL testing using an ORL meter or an OLTS
Figure 4-7 shows a test setup for measuring the ORL and the optical loss. ORL is measured using an ORL meter (or
an ORL test set). The ORL meter includes a source and an optical power meter (OPM) to measure reflected power.
Some OLTS units can perform this test, making a dedicated ORL meter unnecessary—either one can provide a total
end-to-end ORL of the system.
CO
Voice
Data
FDH
Drop
Terminal
Splitter
1XN
WDM
Coupler
Distribution Fiber
Drop
ONT
OLT
Optical
Video
Transmitter
EDFA
Patch Panel
Patch Panel
Drop
Terminal
ONT
Figure 4-8. Testing the bidirectional ORL from the CO to the drop terminal
38 FTTx PON Guide EXFO
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4.4.2 Procedure using an ORL meter or an OLTS
The ORL meter should be calibrated and referenced. Refer to the user guide supplied with the instrument for complete
information. Before connecting or splicing cables, measure the ORL for each splitter branch separately. Perform the ORL
test in both directions. Check for uniformity at the different splitter ports. Once all connections have been made,
measure end-to-end ORL.
Note: The higher the ORL reading, the better.
CO
Voice
Data
FDH
Drop
Terminal
Splitter
1XN
WDM
Coupler
Distribution Fiber
Drop
ONT
OLT
Optical
Video
Transmitter
EDFA
Patch Panel
Patch Panel
Drop
Terminal
ONT
Figure 4-9. Testing the ORL from the CO to the drop terminal
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FTTx PON Guide
EXFO 39
4.4.3 ORL testing using an OTDR
The OTDR is a single-ended testing method. It sends a pulse width into the fiber and measures the Raleigh scattering
back to its detector. From the trace generated, the ORL will be calculated as the area under the curve. This method will
have an accuracy of ±2 dB. The main advantage when using an OTDR is to display any high reflective points that need
to be fixed. It could be a bad splice or a dirty connector.
4.4.4 ORL measurement procedure using an OTDR
To perform a complete measurement with an OTDR, it is always recommended to use a pulse suppressor box (PSB) at
the connector entrance and at the end of the DUT. The PSB should be the same type of fiber used in the network to
avoid mode field diameter (MFD) mismatch. All connectors on the pulse suppressor box should be clean and show no
sign of damage. Figure 4-11 shows a test setup for measuring the ORL and the optical loss from the ONT to the OLT.
Poor ORL value (based on
28 dB specification)
Good ORL values
Figure 4-10. ORL results
40 FTTx PON Guide EXFO
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Since after the splitter there is
always a recovery zone (dead
zone) and also the splitter
attenuates the ORL that
comes from the OLT side
when testing from the ONT, it
is recommended to measure
the ORL from the OLT up to
the splitter as well. A pass/fail
threshold for ORL and
reflectance could be set in the
OTDR setup to quickly
highlight high ORL and the
most contributor of it. The
Figure 4-12 illustrates high
reflective points at event 2 that
failed the limit and should be
fixed.
FDH
ONT
Drop
Drop
Terminal
CO
Splitter
1XN
Distribution Fiber
ONT
Voice
Data
WDM
Coupler
OLT
ONT
Drop
Terminal
Patch Panel
Patch
Panel
EDFA
Optical
Video
Transmitter
ONT
Figure 4-11. ORL measurement for the ONT to the OLT.
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FTTx PON Guide
EXFO 41
4.5 Test 2: Bidirectional Loss Testing
Optical loss is defined as the difference in power
level between the transmitting source and the
receiving power meter. The total optical
system/link loss is the sum of the insertion loss
(IL) of the OLT connector, WDM coupler, splices,
fiber attenuation, splitter, ONT connector and any
faulty connector matings. IL is the loss of optical
energy resulting from the insertion of a
component or device in an optical path.
When the network is designed, a loss budget is
established in accordance with standard values.
This is a detailed analysis to ensure that the
receiver will receive the level of power required for
error-free transmission. The loss budget takes into
account the transmitter power and the receiver
sensitivity, as well as the expected loss of every
optical component in the network. The loss budget
requirement for the PON, based on ITU-T,
is shown in Table 4-2.
42 FTTx PON Guide EXFO
Figure 4-12. An event that failed the reflective limit
www.EXFO.com
Attenuation 2 (dB)
ORL (dB)
Class A
Class B
Class B+
IEEE802.3ah
Class C
ITU-T Rec.
Min.
Max.
Min.
Max.
Min.
Max.
GPON
>32
5
20
10
25
BPON
32
5
20
10
25
Min.
Max.
Min.
Max.
15
30
15
30
1000BASE-PX
10 km
20 km
Min. Max. Min. Max.
G.984.2
G.983.1
See Table 4-3
G.9821
G.983.3
EPON
D
U
20
5
15
19.5 10 23.5
20
20
24
24
Table 4-2. PON loss budget table
BPON
Class B+
Down
Min.
Bit rate (Mbit/s)
Up
Max.
622.08
Min.
Max.
Standards
155.52
Video overlay (dB)
9
27
13
29
IPTV (dB)
10
28
10
28
G.983 series
Table 4-3. Class B+ loss budget table
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FTTx PON Guide
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The splitters in a PON cause an inherent loss because the input power is divided between several outputs. Splitter loss
depends on the split ratio and is approximately 3 dB for a 1:2 splitter, increasing by 3 dB each time the number of
outputs is doubled. A 1:32 splitter has a splitter loss of at least 15 dB. This loss is seen for both downstream and
upstream signals. Splices or connectors at the splitter ports create an additional loss.
An example of a PON loss budget is shown in Table 4-4. In this example, no loss from dispersion or any non-linear
effects are taken into account (only 1 dB loss would be expected for very high bit-rate systems at 1550/1490 nm).
Based on the worst-case total loss of 25 dB (at 1310 nm), this system would meet a class B loss budget but with no
margin. The worst loss comes from the splitter (68%), and its loss would need to be improved, otherwise class C
transmission would be required to guarantee the loss margin.
Loss (dB)
Splitter (1:32)
~ 16-17
WDM coupler (1:2)
~ 0.7-1.0
Splice (fused)
~ 0.02-0.05
Connector (APC)
~ 0.2
Fiber G.652C
~ 0.35/km
Worst case: 1310 nm
Total loss (dB)
1310 nm
Minimum budget
loss class
Number/Length
1
1
4
2
18.2 km
Total Loss (dB)
17
1
0.2
0.4
6.4
Table 4-4. A typical loss budget scenario (worst case: 18.2 km maximum)
44 FTTx PON Guide EXFO
25.0
Maximim of
class B
4.5.1 Loss testing using an OPM
and an OLTS
Loss can be measured using a separate
source and an optical power meter (OPM).
A basic OLTS consists of a light source
and an OPM, while an advanced OLTS
consists of a light source and OPM
combined in one unit and is particularly
useful for bidirectional testing, automatic
referencing and results analysis. Some of
the more advanced OLTS units can
perform automatic bidirectional end-toend loss and ORL tests together, also
providing an estimate of the link distance.
www.EXFO.com
The following considerations are important when selecting an OLTS for PON applications:
• Some OLTS models are automated—automated testing reduces testing time and risk of operator errors
• A high dynamic range allows for testing of very lossy components, such as the splitter and/or increasing the distance
coverage
• An integrated talk-set facilitates bidirectional communication between technicians performing end-to-end tests
• Dual- or triple-wavelength (1310/1490/1550 nm) testing capability is essential for testing PONs based on legacy
fibers showing larger attenuation compared to the more recent vintages. Testing at the three service wavelengths
ensures knowledge of loss budget for each service and is especially critical for meeting video quality requirements.
• An FTTx-optimized interface will facilitate the comprehension of test results displayed by the instrument. Having the
results tagged with FTTx-related terms will also greatly reduce the amount of manipulations when the reporting has
to be performed back at the office
• A fiber inspection probe is an essential tool for fiber deployment; some OLTS models will allow connecting the probe
directly onto the instrument, thus eliminating the need to bring an additional hand-held display in the field
For further information on choosing and using an OLTS, refer to the following articles from our website
(www.EXFO.com):
• How to Choose an Optical Loss Test Set
http://documents.EXFO.com/appnotes/anote021-ang.pdf
• Accurate Loss Testing Made Easy
http://documents.EXFO.com/appnotes/pnote006-ang.pdf
• Loss Measurement in Fiber-Optic Networks
http://documents.EXFO.com/appnotes/pnote007-ang.pdf
www.EXFO.com
FTTx PON Guide
EXFO 45
4.5.2 Loss measurement procedure using an OLTS
To perform automatic loss testing using two OLTS units,
four steps are usually required (refer to the user guide
supplied with the instrument for detailed information):
Bad loss
results
• Offset nulling (if required by the instruments)
compensates for detector noise and internal offsets—
some test units do not require this step
Good loss
results
• Test setup (on both instruments) allows for the
selection of the wavelength(s) and other test
parameters
• Referencing (on both instruments) is necessary to
measure loss through the fiber only, and not through the
test jumpers and accessories—some units automatically
perform this step
Figure 4-13. FOT-930 loss results
• Test initialization (on initializing instrument)—some units automatically perform this step for both instruments
The loopback method of referencing can be used and must be performed on each OLTS. The loopback reference is
performed by connecting a test jumper at each unit’s source port and looping it back to the same detector port of the unit.
The measured power level at the detector port is stored as a reference (see Figure 4-14). Another, more accurate,
option is the side-by-side referencing method, which is performed by connecting the source of unit A to the detector
port of unit B and the source of unit B to the detector port of unit A.
46 FTTx PON Guide EXFO
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Once both OLTS units have been referenced, the jumper on each
OLTS is disconnected from the detector port and connected to the
fiber under test (FUT). The test is initiated on one OLTS. The source
of this OLTS sends light through the link. The other OLTS measures
the received power values and communicates this information to the
initiating instrument, which compares the quantity of light received
with the reference measurement. The difference between the two
measurements corresponds to the average link loss.
An OTDR operates by sending a high-power pulse of light down the
fiber and measuring the light reflected back. Every event in the link
(i.e., each optical component and optical fault) causes a reflection or
an optical loss, or both. Fiber ends and fiber breaks, as well as
connectors and other components, each reflect a small part of the
pulse back to the OTDR. The OTDR uses the time it takes individual
reflections to return to determine the distance of each event.
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Adapter
Figure 4-14. OLTS loopback referencing
Reflection
Power (dB)
4.5.3 Loss measurement using an OTDR
During PON installation, it is important to ensure that each cable
section meets or exceeds the cable specifications. This can best be
accomplished by using an OTDR. Unlike an OLTS, which
characterizes the overall loss of an entire link using two instruments,
an OTDR provides a detailed map of all of the section losses (see
Figure 4-15), allowing users to locate and characterize every
individual element in the link, including connectors, splices, splitters,
couplers and faults.
Reference Patchcord
Loss
Slope
shows
fiber attenuation
Figure 4-15. Cable section mapping from splitter input to
WDM coupler output
FTTx PON Guide
EXFO 47
Optical fibers uniformly backscatter a small portion of the light over their entire
length. The OTDR measures this backscattered light to determine the
attenuation of the fiber. Sudden reductions in the level of backscattered light
correspond to optical losses due to splices or other events. For instance, the
typical attenuation of the G.652.C fibers can be measured over the ranges of
wavelengths used in the PON, typically:
• 0.33 dB/km at 1310 nm (0.35 dB/km for worst case)
• 0.21 dB/km at 1490 nm (0.27 dB/km for worst case)
• 0.19 dB/km at 1550 nm (0.25 dB/km for worst case)
Larger spectral attenuations may be observed in old G.652 fibers.
Figure 4-16. EXFO’s FTB-7400E OTDR
housed in the FTB-200 Compact Platform
The faults that can be detected by the OTDR include misalignments and mismatches, angular faults, dirt on connector
ferrules, fiber breaks and macrobends. Macrobends are unwanted events that are caused when a fiber is bent tighter
than its minimum bend radius (such as tie-wrap too tight) and can easily be detected by comparing the loss at 1310,
1490 and 1550 nm, due to the fact that they have more significant losses at higher wavelengths (1550 nm) than at
lower ones (1310 nm). The best OTDR wavelength available for macrobending detection is 1625 nm (the longer the
wavelength, the better).
Each fiber should be tested from the OLT at the CO to the splitter, as well as from the splitter to the ONT
(bidirectionally if possible). Several types of events, such as mismatched core sizes, generate different levels (gains
vs. losses), depending on whether the light comes from one direction or the other. Bidirectional testing provides more
accurate results since the loss values measured in each direction can be averaged.
48 FTTx PON Guide EXFO
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Another important consideration when using an OTDR is the dead-zone phenomenon. Due to the fact that the detector
in the OTDR is extremely sensitive, it may become saturated by strong reflections, such as from the OTDR output
connector and from the first event (connector) in the network. Often, the longest dead zone occurs at the first
connection (the OTDR bulkhead connector). Since it is impossible to measure loss within a dead zone, loss due to
splices and connectors close to the OTDR launch point cannot be determined under ordinary circumstances. However,
the use of a pulse suppressor box (PSB) between the OTDR and the FUT can work around this problem. The PSB
contains a length of fiber-optic cable that allows the first connector, as well as events hidden by the dead zone, to be
included in the link loss measurement.
Loss from the last connector of the FUT can be measured in the same way by connecting the PSB to the last connector.
The PSB enables the OTDR to compare backscattering levels before and after the event in order to calculate the
connector loss.
For PON testing, the OTDR should be capable of testing at either
three wavelengths (1310, 1490 and 1550 nm). In many cases,
testing at 1550 nm is considered adequate to cover the 1490 nm
region at the same time. It is generally agreed that the fiber
attenuation at 1490 nm is approximately 0.02 dB greater than at
1550 nm, which for a maximum of 20 km adds 0.4 dB of total
attenuation. This is usually true for very recent vintage fiber (late
’90s and younger), especially for the G.652.C. However, this may be
questionable for older vintage fiber (early ’90s and older) when
G.652.C did not yet exist and when little interest was placed on the
water peak (E-band).
Figure 4.17. FTTx PON OTDR trace
www.EXFO.com
FTTx PON Guide
EXFO 49
For testing long fibers or lossy components, high dynamic range is necessary, whereas when characterizing a discrete
event, a short pulse is often required. These two features contradict each other: a longer pulse will provide a higher
dynamic range, while a shorter pulse will come with a lower peak power, limiting the dynamic range.
This is where a PON-optimized OTDR is important, such an OTDR is different than a standard OTDR unit in many
aspects such as available pulse width and the receiver bandwidth, which results in different spatial resolutions.
Moreover, an OTDR could face a significant loss in a PON network, for example a 1x32 splitter (16 to 17 dB). An
important question that arises is: What will happen when the signal crosses the splitter? With a standard OTDR, it may
not have enough dynamic range to see after the splitter—and increasing the pulse width it will not have enough
resolution.
The OTDR analysis software must be well-designed to
thoroughly locate all possible types of events, such as
reflections caused by connectors, fiber breaks or fiber ends,
as well as losses caused by splices or macrobends in addition
to gains caused by imperfect core alignments or diameter
differences (delta variations in mode-field diameter). A goodquality OTDR should be able to clearly point out all the types
of events on the trace; to make them easily identifiable to the
user and to list the events in an events table.
It is important to select an option that provides a welldesigned, easy-to-use interface and includes features such
as signal averaging, report generation and printing, as well as
an automatic mode of operation. Some OTDRs also include a
built-in visual fault locator (VFL).
50 FTTx PON Guide EXFO
Figure 4-18. Standard OTDR testing through a splitter demonstrating
lack of resolution
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For further information on using an OTDR, refer to the following articles on our website (www.EXFO.com):
• Bidirectional OTDR Testing: Multimode vs. Singlemode Fibers
http://documents.EXFO.com/appnotes/anote043-ang.pdf
• Optimizing OTDR Measurement Parameters
http://documents.EXFO.com/appnotes/anote076-ang.pdf
• Fiber-Optic Testing Challenges in Point-to-Multipoint PON Testing
http://documents.EXFO.com/appnotes/anote110-ang.pdf
• An Innovative Solution for In-service Troubleshooting on Live FTTH Networks
http://documents.EXFO.com/appnotes/anote130-ang.pdf
• Selecting the Right OTDR
http://documents.EXFO.com/appnotes/anote142-ang.pdf
• OTDR PON Testing: The Challenges—The Solution
http://documents.EXFO.com/appnotes/anote201-ang.pdf
www.EXFO.com
FTTx PON Guide
EXFO 51
4.6. OTDR Settings
Before using an OTDR, it is important to understand the test parameters to be able to test them correctly. Although
many OTDRs have an Auto mode in which the instrument attempts to determine the optimal settings for the link under
test, in some situations, it may be necessary to manually set the parameters in order to obtain the desired results. When
testing at several different wavelengths, the same settings for all wavelengths or different settings for each individual
wavelength can be used. In addition, there are usually options for storing test results in a database and for printing
reports. The main test parameters are described below. Refer to the instrument’s user guide for complete information.
• Distance range: Determines the maximum distance at which the OTDR will detect an event.
• Pulse width: Determines the time width (duration) of the pulse that is sent by the OTDR. A longer pulse travels
further down the fiber and improves the signal-to-noise ratio (SNR) but results in less resolution, making it more
difficult to separate closely spaced events. A longer pulse also results in longer dead zones. In contrast, a shorter
pulse width provides higher resolution and shorter dead zones, but less distance range and lower SNR. Generally, it
is preferable to select the shortest possible pulse width, enabling to see everything and then proceed to make further
adjustments for optimization.
Note that when testing downstream in an FTTx network, the optical power of the OTDR pulse must be large enough
to go through the splitter(s) and the dynamic range must be high.
• Acquisition time: Sets the acquisition duration (time period during which test results are averaged). In general,
longer acquisition times produce cleaner traces (especially with long-distance traces) due to the fact that as the
acquisition time increases, more of the noise is averaged out; this averaging increases the SNR and the ability for
the OTDR to detect small and closely spaced events.
When performing a quick test, in order to locate a major fault such as a break, a short acquisition time should be
used (e.g., 10 s). To fully characterize a link with optimal precision and to make sure the end-to-end loss budget is
respected, a longer acquisition time (45 s to 3 min) is preferable.
52 FTTx PON Guide EXFO
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• Pass/warning/fail criteria: Some OTDRs can display a message at the end of an analysis to inform the user if one
or more events exceed a preset threshold. Separate warning and fail thresholds can be set for each type of
measurement (i.e., splice loss, connector loss, reflectance, fiber section attenuation, total span loss, total span length,
and ORL). This feature can be used to ensure that each optical component in the link meets its acquired values.
4.6.1 Procedure
During installation, OTDR testing should be performed after installation of each segment of the network. Figures 4-19
and 4-20 show examples of tests performed from the end of the last installed link toward the OLT in the CO.
Bidirectional testing with an OTDR is important because for some events, such as for a splice between two fibers with
a slightly different geometry, the loss found with an OTDR varies for different testing directions. Averaging the losses
from a bidirectional measurement will eliminate the impact of fiber geometry and will provide the true loss values.
It is sometimes useful to test from the CO toward the splitter(s) and all the way to the ONTs. However, when many
distribution fibers are being tested, the reflection of each of the different fibers will be combined and the interpretation
of the trace OTDR will become more difficult and often, simply not possible.
For further information, refer to the following article on our website (www.EXFO.com):
• Fiber-Optic Testing Challenges in Point-to-Multipoint PON Testing
http://documents.EXFO.com/appnotes/anote110-ang.pdf
www.EXFO.com
FTTx PON Guide
EXFO 53
CO
Voice
Data
FDH
Drop
Terminal
Splitter
1XN
WDM
Coupler
Distribution Fiber
Drop
ONT
OLT
Optical
Video
Transmitter
EDFA
Patch Panel
Drop
Terminal
Patch Panel
ONT
Figure 4-19. Testing from an ONT or drop terminal to the CO
CO
Voice
Data
FDH
Drop
Terminal
Splitter
1XN
WDM
Coupler
Distribution Fiber
Drop
ONT
OLT
Optical
Video
Transmitter
EDFA
Patch Panel
Patch Panel
Drop
Terminal
ONT
Figure 4-20. Testing from the splitter output to the CO
54 FTTx PON Guide EXFO
www.EXFO.com
Figure 4-21. Simplified OTDR trace: Events 1 to 2 is the PSB; event 2 is the drop box; events 3 and
4 are splices; event 5 is the splitter and event 6 is the patchpanel at the CO.
www.EXFO.com
FTTx PON Guide
EXFO 55
5. Service Activation Testing
5. Service Activation Testing
The following tests should be performed when first activating the network or when connecting an ONT.
5.1 OLT (Initial Service Activation Only)
An optical power measurement at the OLT is required to ensure that sufficient power is delivered to the ONTs. This is
only done during the initial activation because it cannot be repeated without interrupting service for the entire network
once the network has been connected. To perform this measurement, disconnect the feeder fiber and measure the
power directly at the output of the WDM (combining video and OLT signals). Two methods can be used:
• An optical power meter (OPM) measures the total optical power: optical filters can be used to measure the power
at each individual wavelength, one wavelength at a time
• A wavelength-demux PON power
meter measures the power of
each wavelength simultaneously:
power thresholds can be set in
order to provide pass, warning or
fail status for each wavelength
After reconnecting the feeder
fiber, perform a similar test at the
FDH, measuring the power at
each splitter output.
CO
FDH
Splitter
1XN
Voice
Data
ONT
Drop
Distribution Terminal
Fiber
WDM
Coupler
ONT
OLT
Optical
Video
Transmitter
Drop
ONT
EDFA
Patch Panel
Patch Panel
Drop
Terminal
ONT
Figure 5-1. PON power meter connected between the drop and the ONT
www.EXFO.com
FTTx PON Guide
EXFO 57
5.2 Optical Network Terminals (ONTs)
Each time a new ONT is added to the PON, the downstream and upstream optical power at the drop should
be measured. The preferred method is to use a wavelength-demux PON power meter that can be connected as a passthrough device. Another method is to use an OPM and filters; however, this method does not allow measurement of the
upstream signal, nor pass-through operation.
Figure 5-1 shows a PON power meter connected as a pass-through device between the drop and the ONT. This type of
instrument simultaneously measures the downstream power at 1550 and 1490 nm and the upstream power at 1310 nm.
Unlike an OPM, which measures the average power of an optical signal, the PON power meter detects the power of the
traffic bursts in order to provide accurate measurements.
5.3 Multiple Testing Locations
It is important to keep in mind that FTTH networks link one location to multiple locations, also called point-to-multipoint
networks (P2MP), where each drop fiber corresponds to a specific customer or optical network terminal (ONT),
as opposed to legacy networks, where a fiber typically links one location to another.
In terms of data storage, PON service activation therefore brings about two new dimensions:
1. More than one test location may be required, typically two or three
2. Results should be linked to customers or ONTs instead of fibers
Verifying optical levels at various locations along the same fiber path will help pinpoint problems and/or defective
components before activating a customer’s service. Since FTTH network problems are often caused by dirty or
damaged connectors, component inspection greatly reduces troubleshooting, as power levels are verified for each
network section. It is also highly recommended to inspect each connection point using a fiber inspection probe, such
as the FIP-400, before each power measurement (see Figure 5.2).
Typical test locations include the splitter cabinet (1), also called FDH, the drop terminal (2) and the customer premises (3):
58 FTTx PON Guide EXFO
www.EXFO.com
CO
FDH
Voice
Data
WDM
Coupler
ONT
Drop
Terminal
Splitter
1XN
IPTV
Distribution Fiber
ONT
OLT
RF
ONT
Optical
Video
Transmitter
EDFA
Patch Panel
Patch Panel
Drop
Terminal
1
ONT
2
3
Figure 5.2. PON power meter measurements at different locations
5.4 Storing Data during Service Activation
Data collected during activation must be classified, included in a report and can also be
included in a data base for future reference.
An advanced PON power meter will feature a PON adapted storage interface which
allows saving results per OLT or central office (CO), per ONT and even per test location.
This greatly facilitates data management and reporting.
Figure 5.3. The PPM-350C’s PONadapted graphical user interface—
storage screen
www.EXFO.com
FTTx PON Guide
EXFO 59
Bit Rate
(Mbit/s)
Class
155.52
A
B
C
A
B
C
622.08
1000 (nominal)
1244.16
2488.32
A
B
C
A
B
1490 nm Power (dBm)
OLT Tx
ONT Rx
Min Max
Sens.
Over
-6
0
-27
-5
-4
+2
-30
-8
-2
+4
-33
-11
-6
-1
-27
-6
-1
+4
-27
-6
-1
+4
-32
-11
-1
+4
-24
-1
+4
-27
-3/-2 +2/+3 -24/-23 -3/-8
-2
+3
-28
-7/-13
+2
+7
-29
-8/-14
Standards
G.983/G.984 series
G.983/G.984 series
EPON: 1000BASE-PX10
EPON: 1000BASE-PX20
G.983/G.983 series
G.984 series
C
Table 5-1. PON optical loss budget requirements for single-fiber topology (Rx max. power sensitivity
is called “overload”)
The downstream power at 1550 and
1490 nm must meet the minimum
ONT receiver sensitivity (depending on
the PON class). The upstream power
should correspond to the ONT
specifications. If the optical power level
is insufficient, refer to Chapter 6 and
perform the troubleshooting steps.
Perform other troubleshooting steps as
necessary to correct the problem.
Similarly, the upstream power at 1310 nm
must meet minimum criteria to be
properly detected at the OLT. Knowing
the worst-case optical power budget, it
is simple to define a minimum optical
power value that the 1310 nm signal
must have at the ONT output.
When all problems have been corrected and the measured power level at the drop is sufficient, connect the drop directly
to the ONT.
Note: It is crucial to understand that the 1310 nm signal transmitted upstream by the ONT is, by nature, a burst and
is not continuous. For this reason, the power of the ONT must be detected with the appropriate instrument.
For further information on using a PON power meter, refer to the following articles on our website (www.EXFO.com):
• Service Activation Made Easy
http://documents.exfo.com/appnotes/anote207-ang.pdf
60 FTTx PON Guide EXFO
• PPM-350 Measurement Techniques
http://documents.exfo.com/appnotes/anote131-ang.pdf
www.EXFO.com
6. Network Troubleshooting
6. Network Troubleshooting
Problems that may occur in an FTTx network
Video
Transmitter
Splitter
1x8
Zone-7
Zone-6
Zone-5
Zone-4
Zone-3
Zone-2
Zone-1
Troubleshooting a PON first involves locating and identifying the source of an optical problem in what may be a complex
optical network topology that includes several splitters, fibers and ONTs. Figure 6-1 shows a multisplitter topology
network with multiple splitters. The numbers indicate the different zones where a problem may be located. If a break
occurs in the cable between the OLT and a
downstream splitter, all ONTs downstream
from that splitter will be affected; however, if
a problem such as macrobending or dirty
connectors causes optical power to be lost
somewhere in the network, only a number of
Neighborhood FDH
downstream ONTs may be affected. Since
the attenuation in fiber optic cables is
ONT
..
proportional to length, distant ONTs receive a
..
CO
FDH
..
1x8
weaker downstream optical signal than
..
.
closer ones. The upstream optical signals
..
..
received at the CO from the more distant
ONT
..
OLT
..
1x4 ..
WDM
ONTs are also weaker and the OLT will
..
Coupler
...
..
detect such decreased performance.
Optical
..
..
..
..
.
ONT
ONT
Figure 6-1. Troubleshooting zones in a typical FTTx network
62 FTTx PON Guide EXFO
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include:
• Optical power level at one or more ONTs does not meet the specified minimum power level
• Loss of signal (no power)
• Increased BER or degraded signal (may be caused by insufficient power)
• Hardware problem with an active component (at ONT or CO)
Since most of the components in the network are passive, a large part of the issues are due to
dirty/damaged/misaligned connectors or breaks/macrobends in the fiber-optical cable. These will affect one, some or
all subscribers on the network, depending on the location of the problem.
Most problems can be located using the following equipment:
• PON power meter: This instrument is connected as a pass-through device, allowing both downstream and upstream
traffic to travel unimpeded. It measures the power at each wavelength simultaneously. It also detects the burst power
of the ATM traffic. This meter can be used for troubleshooting at any point in the network (see Figure 6-4).
• PON-optimized optical time-domain reflectometer (OTDR): A monitoring OTDR provides a graphical trace that
enables to locate and characterize every element in a link, including connectors, splices, splitters, couplers and faults.
OTDRs designed specifically for in-service PON troubleshooting exist. These OTDRs feature a dedicated port for
testing at 1625 or 1650 nm and incorporate a filter that rejects all unwanted signals (1310, 1490 and 1550 nm) that could
contaminate the OTDR measurement. Only the OTDR signal at 1625 or 1650 nm is allowed to pass through the
filter, generating a precise OTDR measurement. In-service OTDR troubleshooting of optical fiber should be done
in a way that does not interfere with the normal operation and expected performance of the information channels.
Testing with the1625 or 1650 nm wavelength does just that.
www.EXFO.com
FTTx PON Guide
EXFO 63
A PON-optimized OTDR does not interfere with the CO’s transmitter lasers because the 1650 nm wavelength complies
with the ITU-T L.41 Recommendation (Maintenance wavelength on fibers carrying signals). This ITU-T recommendation
suggests a 100 nm difference between the OTDR wavelength used for in-service maintenance and the closest
transmission wavelength, in this case, 1550 nm. The addition of a broadband filter, acting as a 1625 or 1650 nm testing
port at the CO’s WDM coupler, may also be beneficial. As a result, the quality of service provided to other subscribers
serviced by the same 1xN splitter is not affected. Armed with this technology, the technician can connect the OTDR’s
1625 or 1650 nm port to the ONT and send the signal toward the CO. If a 1625 or 1650 nm testing port is added to
the CO, it is also possible to perform tests from the CO down to the ONT, but a 1625 or 1650 nm filter may be needed
at each ONT.
For further information on using an OTDR for troubleshooting a PON network, refer to the following articles on our
website (www.EXFO.com):
• An Innovative Solution for In-service Troubleshooting on Live FTTH Networks
http://documents.EXFO.com/appnotes/anote130-ang.pdf
• OTDR PON Testing: The Challenges—The Solution
http://documents.EXFO.com/appnotes/anote201-ang.pdf
64 FTTx PON Guide EXFO
www.EXFO.com
Fiber inspection probe: A fiber inspection probe (FIP) is the most versatile
way to inspect fiber-optic connectors as it allows to:
• Inspect male connectors such as the end of the drop cable and test jumpers
• Inspect female connectors such as the drop terminal or ONT connector ports.
A fiber inspection probe is also the most secure way of inspecting connectors
as it relies on an LCD display or instrument screen to display the connector
image as opposed to a microscope that uses lenses. Some FIPs also allow
taking pictures of connector ports for documentation.
Figure 6-2: OLTS with a fiber inspection probe
connection port
Note on security:
In PON troubleshooting, if one customer
is activated, the whole network receives
the broadcasted DATA signal at 1490 nm
or RF video signal (if present) at 1550 nm
as the network is passive. For this reason,
it is highly recommended to use an FIP
instead of a microscope when
troubleshooting a customer on an active
network.
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Neighborhood FDH
CO
FDH
ONT
Splitter
1XN
OLT
ONT
WDM
Coupler
ONT
Optical
Video
Transmitter
ONT
Figure 6-3.
FTTx PON Guide
EXFO 65
The following table lists problems, their possible causes and the troubleshooting steps to take:
Problem
Possible Cause
Troubleshooting Steps
One ONT is
malfunctioning;
optical power level
at ONT is low
Dirty/damaged connectors or
excessive macrobends after
last splitter
ONT failure
At the end of the drop:
K Measure the optical power
K Inspect the connectors
At the drop terminal:
K Measure the optical power
K Inspect the connectors
At the splitter output:
K Measure the optical power
K Inspect the connectors
One ONT is not working;
no optical power
Fiber break after last splitter
(in distribution fiber or drop cable)
ONT failure
One ONT is malfunctioning;
power level at ONT is OK
ONT hardware problem
K Measure optical power at ONT to confirm that there is no signal
K Measure optical fiber at drop terminal
If signal is present: Problem is in drop cable
K Test drop cable from ONT or from drop terminal using VFL or OTDR
If signal is not present: Problem is in distribution fiber
K Test distribution fiber from drop terminal using OTDR
K Refer to ONT manufacturer’s troubleshooting procedure
Table 6-1. Troubleshooting
66 FTTx PON Guide EXFO
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Problem
Possible Cause
Some or all ONTs connected Dirty/damaged connectors or
to one splitter are
macrobends before splitter
malfunctioning;
power level at ONTs is low
All ONTs connected to one
splitter are not working;
no optical power
Fiber break before last splitter
All ONTs are not working;
no optical power
Break in feeder fiber or
problem at CO
BER increase
Insufficient power at ONT or
ONT hardware problem
Intermittent problem
ONT hardware problem
Troubleshooting Steps
At the splitter output:
K Measure the optical power
K Inspect the connectors
Check for macrobends (inside and outside the FDH)
At the splitter input:
K Measure the optical power
K Inspect the connectors
K Test feeder fiber (or fiber between splitters in the case of multisplitter
link) with OTDR from ONT, drop terminal or splitter
K
K
K
K
K
Test feeder fiber with OTDR from the FDH or the CO
Measure OLT output power
Measure power of video signal before WDM coupler
Measure WDM coupler output power
Check equipment at CO
K Perform steps above as necessary
K Refer to ONT manufacturer’s troubleshooting procedure
K Refer to ONT manufacturer’s troubleshooting procedure
Table 6-1. Troubleshooting (continued)
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FTTx PON Guide
EXFO 67
CO
Voice
Data
FDH
WDM
Coupler
ONT
Drop
Terminal
Distribution Fiber
Splitter
1XN
ONT
OLT
ONT
Optical
Video
Transmitter
EDFA
Patch Panel
Patch Panel
Drop
Terminal
ONT
Figure 6-4. Using a PON power meter for troubleshooting various points in the network
68 FTTx PON Guide EXFO
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7. Abbreviations and Acronyms
ADS
ADSL
APC
APD
ATM
BER
BLEC
BPON
CD
CDMA
CLEC
CO
CVD
CWDM
DBS
DFB
DSL
DSLAM
DUT
DWDM
Additional digital service
Asymmetric digital subscriber line (copper based)
Angled physical contact/angled polished
connector
Avalanche photo diode (detector)
Asynchronous transfer mode protocol
Bit error rate (ITU-T uses bit error ratio)
Building local exchange carrier
Broadband passive optical network
Chromatic dispersion
Collision detected multiple access
Competitive local exchange carrier
Central office
Chemical vapor desposition
Coarse wavelength-division multiplexing
Direct broadcast service
Distributed-feedback (laser)
Digital subscriber line (copper based)
Digital subscriber line access multiplexer
Device under test
Dense wavelength-division multiplexing
70 FTTx PON Guide EXFO
EDFA
EFM
EFMA
EPON
FBT
FCC
FDH
FDT
FEC
FC
FO
FP
FSAN
FTTB
FTTC
FTTCab
FTTH
FTTN
FTTP
FTTx
Erbium-doped fiber amplifier
Ethernet in the first mile
Ethernet-in-the-first-mile alliance
Ethernet-ready passive optical network
Fused biconic taper (fiber coupler/splitter)
Federal communications commission (US)
Fiber Distribution Hub
Fiber Distribution Terminal
Forward Error Correction
Fiber Collector
Fiber-optic
Fabry-Perot (laser)
Full-service access network
Fiber-to-the-building
Fiber-to-the-curb
Fiber-to-the-cabinet
Fiber-to-the-home
Fiber-to-the-node
Fiber-to-the-premises
Fiber-to-the-x, where x = (H)ome, (C)urb,
(B)uilding, (N)ode, (P)remises, etc.
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FUT
GEM
GPON
HDD
HDSL
Fiber under test
GPON encapsulation mode
Gigabit-capable passive optical network
Horizontal direct drilling
High-bit-rate digital subscriber line
(copper based)
HDTV
High-definition television
HFC
Hybrid fiber coaxial transmissions
IEC
International electrotechnical commission
IEEE
Institute of electrical and electronic engineers
ILEC
Incumbent local exchange carrier
IP Internet protocol
IPTV
Internet protocol television
ITU
International telecommunication union
ITU-T
International telecommunication union—
telecommunications standardization sector
wavelength
LFD
Live fiber detector
MAN
Metropolitan area network
MDU
Multi-Dwelling Unit
MFD
Mode-field diameter
MLM
Multilongitudinal mode (Laser)
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MM
MMF
MWM
NF
OC
ODN
ODU
OLT
OLTS
ONT
ONU
OPM
ORL
OSA
OSC
OSNR
OSP
OTDR
P2MP
P2P
PBX
Multimode
Multimode fiber
Multiwavelength meter
Noise figure (noise from an optical amplifier in dB)
Optical carrier (transport rate)
Optical distribution network
Optical distribution unit
Optical line terminal/termination
Optical loss test set
Optical network terminal/termination
Optical network unit (non-transmitting ONT)
Optical power meter
Optical return loss
Optical spectrum analyzer
Optical service channel
Optical signal-to-noise ratio
Outside plant
Optical time-domain reflectometer
Point-to-multipoint
Point-to-point
Private branch exchange
FTTx PON Guide
EXFO 71
PC
PIN
PLC
PMD
PON
POTS
PSB
PSTN
QoS
RBOC
Rec
RLEC
RT
Rx
SC
SDH
SM
SMF
SNR
SONET
Polished connector
Positive-insulator-negative (detector)
Planar lightwave (or lightguide) circuit
Polarization mode dispersion or physical
medium dependent
Passive optical network
Plain old telephone service
Pulse suppressor box
Public switched telephone network
Quality of service
Regional Bell operating company
ITU-T Recommendation
Rural local exchange carrier
Remote terminal
Receiver
Supervisory channel or service channel
Synchronous digital hierarchy
Singlemode
Singlemode fiber
Signal-to-noise ratio
Synchronous optical network
72 FTTx PON Guide EXFO
STM
TDM
TDMA
TIA
Tx
UPC
VDSL
VFL
VOD
VoIP
WDM
xDSL
Synchronous transfer mode
(SDH transfer rate)
Time-division multiplexing
Time-division multiple access
Telecommunications Industry Association
Transmitter
Ultra-polished connector
Very-high-speed digital subscriber line
(copper based)
Visual fault locator
Video-on-demand
Voice over Internet protocol
Wavelength-division multiplexing
Generic digital subscriber line (copper based)
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8. List of ITU-T PON Recommendations
Fiber Recommendations
G.650.1: Definitions and test methods for linear, deterministic attributes of single-mode fibre and cable
G.650.2: Definitions and test methods for statistical and non-linear related attributes of single-mode fiber and ca
G.652: Characteristics of a single-mode optical fibre and cable
G.653: Characteristics of a dispersion-shifted single-mode optical fibre and cable
G.654: Characteristics of a cut-off shifted single-mode optical fibre and cable
G.655: Characteristics of a non-zero dispersion-shifted single-mode optical fibre and cable
G.656: Characteristics of a fibre and cable with non-zero dispersion for wideband optical transport
G.657: Characteristics of a bending loss insensitive single mode optical fibre and cable for the access network
Component and sub-system Recommendations
G.671: Transmission characteristics of optical components and subsystems
PON System and network Recommendations
G.983 series:
G.983.1: Broadband optical access systems based on Passive Optical Networks (PON)
G.983.2: ONT management and control interface specification for B-PON
G.983.3: A broadband optical access system with increased service capability by wavelength allocation
G.983.4: A broadband optical access system with increased service capability using dynamic bandwidth assignment
G.983.5: A broadband optical access system with enhanced survivability
G.983.9: B-PON ONT management and control interface (MCI) support for wireless local-area network interfaces
G.983.10: B-PON ONT management and control interface (OMCI) support for digital subscriber line interfaces
74 FTTx PON Guide EXFO
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G.984 series
G.984.2: Gigabit-capable Passive Optical Networks (G-PON): Physical Media Dependent (PMD) layer specification
G.984.4: Gigabit-capable Passive Optical Networks (G PON): ONT management and control interface specification
G.984.5: Enhancement band for gigabit capable optical access networks
G.984.6: Gigabit-capable Passive Optical Networks (GPON): Reach extension
G.985: 100 Mbit/s point-to-point Ethernet based optical access system
IEEE 802.3ah—2004: IEEE standard for information technology, telecommunications and information exchange
between systems—local and metropolitan area networks. Specific requirements Part 3: Carrier Sense Multiple Access
with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications Amendment: Media Access
Control Parameters, Physical Layers and Management Parameters for Subscriber Access Networks
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FTTx PON Guide
EXFO 75
9. Appendix
9. Appendix
PON Classification
1. ONU
1.1 ONU installed inside premises
1.2 ONU installed outside premises
2. Drop terminals/drop cables
2.1 ODN installed using drop terminal and drop cables
2.2 ODN installed without drop terminal and drop cables (F2 directly to ONU)
3. Splitter
3.1 ODN using single splitter with maximum split ratio
3.2 ODN using multistage splitter with various split ratios
4. F1
4.1 F1 with no redundancy
4.2 F1 using redundancy
5. Video
5.1 PON without video distribution
5.2 PON including video distribution
5.2.1 PON with overlaid analog RF video
5.2.2 PON with digital IPTV
6. Monitoring
6.1 PON without optical/physical monitoring
6.2 PON with optical/physical monitoring
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FTTx PON Guide
EXFO 77
Notes
78 FTTx PON Guide EXFO
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Notes
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FTTx PON Guide
EXFO 79
Notes
80 FTTx PON Guide EXFO
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FTTxPG.4AN 09/09
For details on any of our products and
services, or to download technical and
application notes, visit our website at
www.EXFO.com.