fttx pon guide testing passive optical...

EditionFourth

FTTx PON GuideTesting Passive Optical Networks

www.EXFO.com

From POTS to PONs

The invention of the telephone in 1876 and the founding of the Bell Telephone Company in 1878 set thestage 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 technologicalbreakthroughs, including the laser and the singlemode optical fiber, that make it possible to transmitmassive amounts of information over long distances using light. Today, more than 90% of US long-distance traffic is carried over optical fibers. However, twisted pairs of copper wire are still widely usedfor 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 fromthe CO to residences and to small- and medium-sized businesses. FTTH is cost-effective because ituses 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.

This pocket guide provides an introduction to FTTH technology and testing during installation,activation and troubleshooting of passive optical networks (PONs).

Acknowledgements

This guide would not have been possible without the enthusiasm and teamwork of EXFO staff, particularly the hardwork and technical expertise of the Product Line Management team and Dr. André Girard, Senior Member of TechnicalStaff, 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 formor 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 2004Legal 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 Contents1. Introduction to FTTx ................................................................................21.1 Description................................................................................................................31.2 Why FTTx is Hot ..................................................................................................71.3 Types of PONs ......................................................................................................91.4 Available Services ..........................................................................................12

2. Network Design and Engineering ..............................14

2.1 Typical FTTx Architecture ..........................................................................142.1.1 Collision Avoidance in Upstream Transmissions ..........17

2.2 FTTx Equipment ................................................................................................172.2.1 Description ............................................................................................172.2.2 Splitters ....................................................................................................21

2.3 Active Equipment ............................................................................................22

3. PON Installation ..........................................................................................243.1 OSPPON Installation ..................................................................................24

3.1.1 OSP Fiber ................................................................................................243.1.2 OSP Splitters, Patch Panels and Fiber Management......253.1.3 OSP Splices ..........................................................................................253.1.4 OSP Drop Terminals ......................................................................25

3.2 MDU Installation ................................................................................................263.2.1 The Fiber Distribution Hub (FDH) ......................................263.2.2 The Riser Cables ..............................................................................263.2.3 The Fiber Collector (FC) ............................................................283.2.4 The Fiber Distribution Terminal (FDT)..............................283.2.5 The Drop Cable ..................................................................................28

4. PON Installation Testing ..............................................................304.1 Connector Inspection and Maintenance ......................................314.2 Performing the Tests........................................................................................344.3 Test Setup for ORL and Optical Loss Measurment............354.4 Test 1: ORLTesting........................................................................................37

4.4.1 ORL Testing Using an ORL Meter or an OLTS ......384.4.2 Procedure Using an ORL Meter or an OLTS............394.4.3 ORL Testing Using an OTDR ................................................404.4.4 ORLMeasurement Procedure Using an OTDR ........40

4.5 Test 2: Bidirectional Loss Testing ......................................................424.5.1 Loss Testing Using an OPM and an OLTS ................444.5.2 Loss Measurement Procedure Using an OLTS ......464.5.3 Loss Measurement Using an OTDR ................................47

4.6 OTDRSettings ....................................................................................................524.6.1 Procedure ................................................................................................53

5. Service Activation Testing ........................................................565.1 OLT (Initial Service Activation only) ..................................................575.2 Optical Network Terminals (ONTs) ..................................................585.3 Multiple Testing Locations........................................................................585.4 Storing Data during Service Activation ........................................59

6. Network Troubleshooting ..........................................................62

7. Abbreviations and Acronyms ..............................................70

8. List of ITU-T PON Recommendations ..................749. Appendix ..................................................................................................................77

www.EXFO.com FTTx PON Guide EXFO 1

1. Introduction to FTTx

1. Introduction to FTTx1.1 DescriptionSinglemode optical fiber, with its almost unlimited bandwidth, is now the transport medium of choice in long-haul andmetropolitan networks. The use of fiber-optic cable—rather than copper cable—significantly reduces equipment andmaintenance costs, while dramatically increasing quality of service (QoS), and now more than ever, many corporatecustomers 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 availableto residential customers and small businesses have been limited to generic digital subscriber lines (xDSL) and hybridfiber-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-speedservices 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 servicesdirectly to residences and small businesses has been the high cost of connecting each subscriber to the CO. A highnumber of P2P connections would require numerous active components and a great deal of fiber-optic cables andtherefore, would have prohibitive installation and maintenance costs. An alternative presently being considered isdeployment of an entirely passive point-to-multipoint (P2MP) topology up to the building, while potentially keepingcopper and wireless premises networks or even providing the fiber up to the subscribers.


The FTTx (fiber-to-the-building, fiber-to-the-home, fiber-to-the-node, fiber-to-the-premises,fiber-to-the-multidwelling-unit, etc.) architectureoffers an attractive solution. With FTTx,a P2MP passive optical network (PON)enables several customers to share the sameconnection, without any active components(i.e., components that generate or transformlight through optical-electrical-opticalconversion) between the CO and customerpremises. A feeder fiber F1 is brought from anoptical line terminal (OLT) in the CO to a fiberdistribution hub (FDH) near a group ofpremises (see Figure 1-1(a)). In the FDH, apassive optical splitter is used to typicallyconnect a number of F2 FD fibers to the samefeeder fiber. Then, each customer premises isprovided with an optical network terminal (ONT) connected on one side to the F2 and on the other side to the premisesnetwork. This P2P architecture dramatically reduces costs of network installation, management and maintenance.

OLT

OLT

OLT

Residential

Splitter

SplitterSplitter

Splitter

Splitter

Splitter

Splitter

OpticalVideo

Transmitter

ONT

ONTONT

ONT

ONT

ONTONT ONT

ONTONT

ONT

ONT

WDMCoupler

WDMCoupler

WDMCoupler

Figure 1-1(a). Providing triple-play services over a high-bandwidth passive optical network

www.EXFO.com4 FTTx PON Guide EXFO

The OLT provides voice and data downstreamtransmission using a 1490 nm wavelengthband, while the ONT provides upstreamtransmission with a 1310 nm wavelengthband, allowing non-interfering bidirectionaltransmission on the same fiber. In addition, theOLT may be connected to one branch of a 2x1wavelength-division multiplexing (WDM)coupler, while the second branch is connectedto a video transmission system. The videois provided downstream only, usually in a 1550 nmwavelength band; once over, the video signal,if it is available, can then be transmitted overthe same 1490 nm band as for voiceand data.

ONT ONT

FDT

FDH

F1

OpticalVideo

Transmitter

WDMCoupler

WDMCoupler

OLT

FDH: Fiber distribution hubFTT: Fiber distribution terminalONT: Optical network terminal

OLT

OLT

WDMCoupler

Figure 1-1(b). Providing triple-play services over a high-bandwidth PON


Variance of the architecture consists of connecting a number of F2s to a drop terminal and then to an F3 drop fiber tothe premises (FTTP). Various shared bandwidths will be provided, depending on customer requirements. So far, typicalsymmetric or asymmetric rates of 155 Mbit/s, 622 Mbit/s, 1.5 Gbit/s and 2.5 Gbit/s have been planned. The protocolof choice is based on the asynchronous transfer mode (ATM) and is typically called Ethernet for EPON; ATM-PON forBPON; ATM and GEM (TDM and Ethernet) for GPON upstream; ATM, GEM (TDM and Ethernet) and ATM/GEM forGPON downstream.

There are many variations of the FTTx architecture(see Figure 1-2), including:

• Fiber-to-the-cabinet (FTTCab)

• Fiber-to-the-curb (FTTC)

• Fiber-to-the-home (FTTH)

• Fiber-to-the-node (FTTN)

• Fiber-to-the-premises (FTTP)

• Fiber-to-the-office (FTTO)

• Fiber-to-the-user (FTTU)

• Fiber-to-the-multidwelling-unit (FTT-MDU)

FTTC

FTTH

ONT

ONT

ONT

ONT

OLT

WDMCoupler

Figure 1-2. Typical FTTx network

= Fiber= Copper


1.2 Why FTTx is HotIn 1995, British Telecom, Bell South, Bell Canada, NTT and five other international telecommunications companies metto form the Full-Service Access Network (FSAN), which was founded to facilitate the development of suitable access-network-equipment system specifications.

The United States legislature adopted the Telecommunications Act of 1996 to promote and reduce regulation in orderto secure lower prices and higher-quality services for American telecommunications consumers and to encourage therapid deployment of new telecommunications technology.

The International Telecommunications Union (ITU-T) turned FSAN specifications into recommendations. The FSANspecification for ATM-based PONs became an international standard in 1998 and was adopted by the ITU asrecommendation G.983.1.

In 2001, the FTTH Council was formed to promote FTTH in North America and to advise the US legislature; thisresulted in the Broadband Internet Access Act of 2001, which provides tax incentives to companies that invest in next-generation broadband equipment.

In 2003, the US Federal Communication Commission (FCC) removed unbundling requirements on newly deployednetworks, such as FTTx (unbundling regional Bell-operating companies’ (RBOCs) obligation to allow competitive localexchange carriers (CLECs) to use their network), making the technology more attractive to major carriers. This meansthat RBOCs can invest in last-mile fiber network—without having to share it with competitors−providing a major incentivetoward the deployment of FTTx networks. Some predict a US$1 billion market for FTTx networks, for RBOCs alone.


8 FTTx PON Guide EXFO www.EXFO.com

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 plantequipment is passive

• New standards such as those established by the ITU-T, the IEC and the Institute of Electronic and ElectricalEngineers (IEEE) have greatly increased the design commonality, survivability and security of PONs, opening theopportunity 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.

FTTx PON Guide EXFO 9www.EXFO.com

1.3 Types of PONsAs 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 Upstream ONU Tx

Nominal bit rate Mbit/s 155.52 622.08 1244.16 155.52 622.08

Operating Wavelengths band nm 1480-1580 1480-1500 1260-1360

1260-1360 (MLM1, SLM)

1280-1350 (MLM2)

1288-1338 (MLM3)

ORLMAX dB >32

Table 1-1. Available PON architectures


TypeGPON (Gigabit-Capable PON)

EPON (Ethernet PON)GPON GPON-ERG

Standard G.984 series 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 demandTriple play

Maxim um Physical distance (OLT to ONT) km 20 Up to 60 (ODN distance) 1000BASE-PX10: 10

1000BASE-PX20: 20

Split ration up to 64 16.32 or 64 (restricted by path loss)

1x161x32 (with FEC or DFB / APD)

Downstream Upstream Downstream Upstream Downstream Upstream

Nominal bit rate Mbit/s 1244.16 / 2488.32 155.52/ 622.08/1244.16 2488.32 1244.16 1000 1000

Operating Wavelengths band nm

-1480-1500-1550-1560

(Enhancement band - for video)

1260-1360 Possibility of using

shorter C-bandwavelengths

downstream and 1550 nm upstream

1480-1500 (Basic band)

OEO (ONU EXT):1260-1360

100BASE-PX10: Downstream:

1490 nm + PIN RxUpstream: 1300 nm

(low-cost FP optics + PIN Rx)100BASE-PX20:

Downstream: 1490 nm + APD RxUpstream:1300nm

(DFB optics + PIN Rx)

1550-1560(Enhancement band- for video

distribution

OEO (OLT EXT):1290-1330

OA:1300-1320

(OBF)

ORLMAX dB >32 15

TDM Time division multiplexingTDMA Time division multiplexing accessOBF Optical band pass filter

ONU Optical network unit (optical network terminal (ONT), when connected to home network)

ODN Optical distribution networkERG Extended range GPON

Table 1-1. Available PON architectures (continued)


Notesa. 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.

Type GPON

Standard ITU-T G.984.1

Optical distribution network class (ODN) A B C A B C a IBP e C+ A B C A B C A B C

Downstream Upstream b

Nom inal bit rate 1244.16 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 – 3 c – 2 + 2

<Plaunch>Max dBm + 1 + 6 + 9 + 4 + 9 + 7 + 5 + 7 0 + 2 + 4 – 1 + 4 + 4 + 2 c + 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 – 3 d – 7 – 8

Table 1-2. GPON/BPON ODN class


Type BPON

Standard ITU-T G.983 seriesOptical distribution network class (ODN) B C A B C A B C B C A B C

Downstream Upstream

Nominal bit rate 155.52 622.08 1244.16 155.52 622.08

<Plaunch>Min dBm – 4 – 2 – 7 – 2 – 2 – 4 + 1 + 5 – 4 – 2 – 6 – 1 – 1

<Plaunch>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

OLT

CO

1490 nm Voice and data1550 nm Overlaid analog RF video (may not be provided)1310 nm Voice and data

Splitter 1 x N

EDFA

WDM Coupler

OpticalVideo

Transmitter

ONT

ONT

Figure 1-3. Wavelengths and services in an FTTx network

1.4 Available Services Figure 1-3 shows the wavelengths and services used in an FTTx network.

Table 1-2. GPON/BPON ODN class (continued)

2. Network Design and Engineering

2. Network Design and Engineering2.1 Typical FTTx ArchitectureFigure 2-1 illustrates the generalarchitecture of a typical FTTxnetwork. At the CO, also referred toas the head-end, the public-switched telephone network(PSTN) and Internet services areinterfaced with the opticaldistribution network (ODN) via the optical line terminal (OLT). The downstream 1490 nm andupstream 1310 nm wavelengthsare used to transmit data and voice.

Analog RF video services areconverted to optical format at the1550 nm wavelength by the opticalvideo transmitter. The 1550 nm and 1490 nm wavelengths arecombined by the WDM coupler andtransmitted downstream together.At present, there are no standardspublished for upstream videotransmission. IPTV is now transmittedover 1490 nm.

Videostorage

OLT

1

32

POTS

Local TVBroadcast

SignalsSatellite

TV Signals

T1-DS-3 TDM

OC-3/OC-12

RF Modulators

RF Modulators

RF Modulators

CO

Residence

Twisted-pair

10/100-Base-TEthernet

Data

TVCoaxcable

1490/1550 nm

1310 nm

..................ONT

ONT

Splitter

EDFA

OpticalVideo

DigitalVideo

AnalogDigitalVideo

VODServer

Class 5 Switch

ATM/Ethernet1P Switch

OpticalVideo

Transmitter

Setupbox

broadcast

WDM Coupler

PSTN

Internet

Figure 2-1. FTTx general architecture



In summary, the three wavelengths (1310,1490 and 1550 nm) simultaneously carrydifferent information and in various directionsover the same fiber.

The F1 feeder cable carries the opticalsignals between the CO and the splitter,which enables a number of ONTs to beconnected to the same feeder fiber. An ONTis required for each subscriber and providesconnections for the different services (voice,data and video). Since one FTTx networktypically provides service to up to 32subscribers, more than 64 with GPON, manysuch networks, originating from the same CO,are usually required in order to servea community.

There are different architectures forconnecting subscribers to the PON. Thesimplest uses a single splitter (see Figure 2-2),but multiple splitters can also be used (seeFigure 2-3).

Splitter

.........

FDHCO

OLTWDM

CouplerOpticalVideo

Transmitter

1x32

ONT

ONT

Figure 2-2. Single splitter FTTx network

Neighborhood FDH

Splitter

.........

........

FDHCO

OLTWDM

CouplerOpticalVideo

Transmitter

1x4

.........

1x8

ONT

ONT

.........

1x8

ONT

ONT

Figure 2-3. FTTx network with multiple splitters


OLT

ONU1 ONU3 ONU5

ONU2 ONU4

OLT

ONU1

ONU2

ONU4

ONU5

ONU3OLT

ONU1 ONU5

ONU2

ONU3

ONU4

Figure 2-4. PON topologies

Splitter

FTTH

FTTH

FTTCVDSL

VDSL

VDSL

ONU

ONU

ONU

FTTC

FTTB

PON

VDSL

OLT

CO

ONT

ONT

ONT

Splitter

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 protectionis 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 thesplitter is brought to an ONT, and short copper-based links (typically VDSL, which provides sufficient bandwidth fortriple-play services over short distances) are used for the final connection (see Figure 2-5); this is also known as fiber-to-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 videosignal at 1550 nm and the upstream voice/data signal at 1310 nm.


2.1.1 Collision Avoidance in Upstream TransmissionsIn the case of the upstream direction (i.e., toward the OLT) of a P2MP PON, collisions of data must be prevented fromdifferent 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 ONTtransmission 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 DescriptionPON 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 opticaldistribution network (ODN) and include splices, connectors, splitters, WDM couplers, fiber-optic cables, patchcords andpossibly drop terminals with drop cables. The non-optical components include pedestals, cabinets, patch panels, spliceclosures and miscellaneous hardware (see Figure 2-6).

CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

FDHSplitter1 X N

Patch Panel

Drop TerminalDrop

Drop Terminal

Distribution FiberONT

ONT

ONT

ONT

Figure 2-6. FTTx equipment for ONU installed outside premises


1260 1360 1460

EO U

1675

O = Original band E = Extended band

S = Short band C = Conventional band

L = Long band U = Ultra-long band

Note = Low wate r-peak fiber

Figure 2-7. Spectral attenuation

Outside plant (OSP) equipment includes the following:

• Fiber-optic cables: the feeder cables form the segment betweenthe CO and the first splitter; distribution fibers link the splitter tothe 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 2-7shows the attenuation in a typical fiber.

• Fiber distribution hub(s) include:

- Cabinets, pedestals, splice enclosures (aerial or buried)

- Splitter(s) (an important component; see section 2.2.2)

- Patch panel(s)

- Fiber-management elements

• 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)


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 theequipment 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 OSPequipment. 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:

- Cabinets, splice enclosures

- Splitter(s) (an important component; see section 2.2.2)

- Patch panel(s)

- Fiber-management elements

FDT

FDT

FDT

FC

FDH

To CO

FC

FDH

FDT

Figure 2-8 (a). High/medium-rise MDU equipment


• 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):

- The FC serves as a junction point between the FDH and few FDTs (see Figure 2-8 (a)).

Outdoor ONT

Indoor ONT

Outdoor FDH

Feeder Cable F1

Outdoor FDT

Figure 2-8 (b). Horizontal/garding style MDU equipment


2.2.2 SplittersThe bidirectional optical branching device used in the P2MP PON is called an“optical power splitter” or simply a “splitter”, which has one input from the F1 portand multiple output ports. Splitters are passive because they require no externalenergy source other than the incident light beam. They are broadband and onlyadd loss, mostly due to the fact that they divide the input (downstream) power.This loss, called “splitter loss” or “splitting ratio”, is usually expressed in dB anddepends mainly on the number of output ports, as shown in Table 2-1. Forinstance, the input (downstream) optical signal is divided equally in cascade orbranches; for instance a 1x2 splitter has only two branches or one split thatbares a 3 dB loss (50% light in each leg). In a 1x4 splitter, another two brancheswill be added to each leg of the original 1x2−split this time adding another 3dB for a total of 6 dB loss. In a 1x8 splitter, two more branches or 1x2 split willbe added to each leg of the original 1x4 split, again adding another 3 dB for atotal of 9 dB loss. A 1x16 splitter will then bare a 12 dB, and a 1x32 splitter willhave a minimum of 15 dB loss, not counting any additional loss due to connections and imperfections (typically 1dB is addedto 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 consequentlya 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 lighttraveling in the upstream direction.

There may be one splitter or several cascaded splitters in an FTTx network, depending on the network topology. ITU-TRecommendation 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.

Table 2-1. Splitter loss

Number of Ports Splitter Loss (dB)(excluding connectors

and excess splitter loss)

2 3

4 6

8 9

16 12

32 15

64 18

22 FTTx PON Guide EXFO

Splitters can be packaged in different shapes and sizes, depending on the basic technology used. The mostcommon 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 and2-10 illustrate the two technologies.

2.3 Active EquipmentThe 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 theanalog RF video overload signal before transmission through the WDM coupler

• The ONT (its electrical power supply and battery backup) located at the customer premises

PON Passive Optical ComponentsSplitter Technology

Fused Biconic Taper (FBT) Fiber

Input Output

1

2 Fused Biconic Taper

b = kn3

PON Passive Optical ComponentsSplitter TechnologyPlanar Waveguide

PLC = Planar Lightwave Circuit

Optical circuit on a substrate made using tools and techniques based on CVD or Icon Exchange based on semiconductor industry

Core

Core

Core

Core

Mask

CladdingSi Substrate

CladdingSi Substrate

Cladding

Cladding

Cladding

Si Substrate

Si Substrate

Figure 2-9. Planar waveguide splitter Figure 2-10. FBT splitter

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3. PON Installation


3. PON InstallationInstallation of PON equipment in an FTTx network can be carried out in many ways and each installation may bedifferent, depending on such factors as the distance from the CO, residential density and distribution urbanism, to namea few. Fiber-optic cables can be installed using the most appropriate aerial- or underground-installation techniques. Theplacement of splitters and other passive components and the types of cabinets used depend on geographical factorsand on the PON topology.

3.1 OSP PON Installation

3.1.1 OSP FiberFiber-optic cable installation is one of the most costly elements in PON deployment. Several methods are available, andthe choice of method depends on various factors, including cost, right-of-way, local codes, aesthetics, etc., and on whetherthe installation is being performed in a new premises development (Greenfield installation) or in an existing developmentover 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 ductinstallation 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 heavymachinery. 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).


3.1.2 OSP Splitters, Patch Panels and Fiber ManagementSplitters and patch panels are usually installed in cabinets mounted on pedestals or fixed on posts, also called “fiberdistribution hubs” (FDHs). The number, type and placement of the splitters depend on the topology of the network andthe number of fibers in the F1 feeder cable (see FTTx Equipment, Figure 2-6).

3.1.3 OSP SplicesSplices can be mechanical or fused. Mechanical splices are the least expensive but have higher insertion loss andbackreflections than fused splices, which have very low loss (0.02 dB) and almost no backreflection but typically requireexpensive and extensive fusion-splicing equipment and a well-trained technician. The number of splices depends onthe cable section lengths used (typical section lengths are ≤ 2 km, 4 km and 6 km). The shorter the length, the easierthe 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 TerminalsDrop terminals are typically used for easing service connection and distribution and, if used, can be aerial, undergroundor located in apartment buildings, depending on the installation. Cable drops between splitter and premises aresometimes pre-connectorized and can be buried or aerial-mounted. They are usually short in length (≤ 30 m).


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 thedemarcation point between the outside network and the in-building network. In somecases, where the number of floors is high like in high-rise building, additional FDHscan 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 canbe mounted on a wall, rack or pedestal.

3.2.2 The Riser Cables As explained in section 2.2.1, riser cables can becomposed of individual fibers going from each port of thesplitter (located in the FDH) to each port of the FDTs orthey can be composed of an MTP cable going from theFDH to the fiber collector (FC). Typically in high-risebuildings, a straight stack riser system with multiplesleeves is available and can be used as channels for theriser cables.

The riser cables can be deployed in the building by using fusion-spliced terminations ora plug and play (pre-engineered) system approach. A pre-engineered solution impliesthat 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 solutionbecomes attractive in Brownfield—where deployment speed is critical.

FDT

FDT

FDT

FC

FDH

F1

To CO

FDH

Figure 3-1. Fiber distribution hubinstallation in MDU

FDT

FDT

FDT

FC

FDH

To CO

F1

Figure 3-2. Riser cable installationin MDU


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)

• Lower cost of components

• Decrease the cost of the labor in the project (less splicing fees)

• 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 General Appreciation

• De-facto approach: contractors are used to splice and the presence of connectorsin 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

• 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)

www.EXFO.com

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 MTPapproach is selected to deploy the riser cables. They are generally mounted on walls in a central location where they are easily accessible.

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.

3.2.5 The Drop CableHorizontal drop cables reach every living unit, where the ONT stands (see Figure 3.1). The dropcable is generally be made of a bend-insensitive fiber that will facilitate their deployment.

FDT

FDT

FDT

FC

FDH

F1

To CO

FC

Figure 3-3. Fiber collector in MDU

Figure 3-4. Structure wiring box (SWB) withONT and battery back-up. (Pictures courtesyof Connexion Technologies)

28 FTTx PON Guide EXFO

4. PON Installation Testing


4. PON Installation Testing The purpose of any fiber-optic network is to perform high-speed, error-free data transmission. Adequate testing during network installationguarantees that products meet specifications, plus it minimizes costlyand time-consuming troubleshooting efforts by locating dirty/damagedconnectors, questionable splices and other faulty components beforethey disrupt service.

One of the most important factors in ensuring proper transmission is controlling the power losses in the network against the link lossbudget specifications from the ITU-T Recommendation and IEEEstandard, which is done by establishing a total end-to-end loss budgetwith sufficient margin, while reducing backreflections to a minimum.This is particularly true for high-power analog RF video signals fromextremely narrowband lasers, since strong backreflections degrade thequality of the video transmission.

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 valuebecause 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.

Figure 4-1. Adequate loss and backreflection testing is important


4.1 Connector Inspection and MaintenanceConnectors are key components that interconnect the entire network elements, which is why maintaining them in goodcondition is essential to ensure that all the equipment operates to their maximum performance—to avoid catastrophicnetwork 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 makingconnections, 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 end-face, 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 orvideoscope after cleaning

MechanicalSection

ConnectorEnd-face

Buffer Coating(~250 to 900 µm)

Zone B: Cladding(125 µm singlemode fiber)

Zone A: Core(~9 µm singlemode fiber)

Figure 4-2: Zone defining the ferrule


• 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 endsand 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.


Is the connector

endfacedamaged or

dirty?

Is the connector

endfaceclean?

Damaged Dirty

No

YesNo

Inspect

Inspect

Connect

Connect

Replace theconnector if

the damagesare critical

Clean it:dry-wet

or hybrid

Figure 4-3. Connector inspection and cleaning procedure

For further information onconnector maintenance, referto the following article on ourwebsite (www.EXFO.com):

Connector Inspection andMaintenance

http://documents.exfo.com/appnotes/anote191-ang.pdf


4.2 Performing the TestsThe 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 testsetup and the test installation. Useful test instruments include an ORLmeter, 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 shouldbe performed. After installing a splitter, end-to-end tests should be performedon the feeder fiber F1 between each splitter output port and the output portof the OLT. When the drop terminals have been installed, tests should beperformed between each drop terminal output port and the patch panel of thefiber distribution hub (distribution fiber F2). This test can also be carried outbetween the drop terminal port and the patch panel of the OLT. This isperformed when the output of the splitter is not connectorized but spliceddirectly to the distribution fiber. Finally, when the drop cable is installed, the linkcan be tested between the drop cable ONU connector and the OLT outputport.

Figure 4-4. EXFO’s cleaning kit

Figure 4-5. FIP-400 video inspection probe


4.3 Test Setup for ORL and Optical Loss Measurement LinkThere 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 onan OTDR. Since communication over the fiber is bidirectional, the ORL must be measuredin both directions. Using an ORL meter or compatible OLTS at each end of the link, the ORLshould be measured first in one direction, then in the opposite direction. Modern OLTS andOTDR units are used for measuring both ORL and optical loss at the same time.

The optical-loss test requires a sequence of twomeasurements. Two OLTS units are firstreferenced together using their individual lightsources. Then, each OLTS sends a calibratedpower value from its light source over the sectionunder test to the other OLTS, which measures thereceived power and calculates the loss.

Figure 4-6. EXFO’s FOT-930MaxTester—a multifunctionhandheld ORL/OLTS

Figure 4-7. FasTest: one-touch, automatedmeasurements in 7 seconds


The OTDR is placed at the ONT and is able to measure the optical-loss andreflectance for each component of the network and the overall loss of the totallink. The ORL is then calculated. The OTDR could also be used to test fromthe OLT to the ONT. Notice that after the splitter, the optical loss and the ORLshould not be directly considered due to two factors: All legs of the splitter willgenerate backscattering if they all have a certain length of fiber and thereforewill not show the true loss after the splitter, all lights coming back will reducethe actual loss of each leg. The ORL after the splitter will be attenuated by thesplitter and therefore should not be consider.

ITU-T recommendations G.983 and G.984 series allow a maximum ORL of 32 dB for a link. IEEE 802.3ah allows a minimumof 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).

Table 4-1. Typical connector ORLs

Note: A larger value indicates less reflection andis therefore better

Connector Type Typical ORL (dB)

UPC 50-55

APC 65-70


4.4 Test 1: ORL TestingORL 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 unitsand is a positive number. Reflectance, on the other hand, is a negative number and is defined as the reflection from asingle 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 foundalong the link. ORL can be a problem in digital high-speed transmission systems but is particularly critical for analogtransmission, such as the 1550 nm CATV signals possibly used in FTTx systems (e.g., analog RF video in a PON). WhileRayleigh backscattering is intrinsic to the fiber and cannot be completely eliminated, reflectance is caused by differentnetwork elements (mainly connectors and components) with air/glass or glass/glass interfaces and can always beimproved by special care or better designs. To optimize transmission quality, backreflection effects (e.g., light-sourcesignal interference or output power instability) must be kept to a minimum. Therefore, attention must be focused onensuring 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


CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

FDHSplitter1 X N

Patch Panel

Drop Terminal

Drop Terminal

DropDistribution FiberONT

ONT

CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

DropONT

ONT

Figure 4-8. Testing the bidirectional ORL from the CO to the drop terminal

4.4.1 ORL testing using an ORL meter or an OLTSFigure 4-7 shows a test setup for measuring the ORL and the optical loss. ORL is measured using an ORL meter (oran 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 totalend-to-end ORL of the system.


CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

FDHSplitter1 X N

Patch Panel

Drop Terminal

Drop Terminal


ONT

CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

DropONT

ONT

Figure 4-9. Testing the ORL from the CO to the drop terminal

4.4.2 Procedure using an ORL meter or an OLTSThe ORL meter should be calibrated and referenced. Refer to the user guide supplied with the instrument for completeinformation. Before connecting or splicing cables, measure the ORL for each splitter branch separately. Perform the ORLtest 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.


4.4.3 ORL testing using an OTDRThe OTDR is a single-ended testing method. It sends a pulse width into the fiber and measures the Raleigh scatteringback to its detector. From the trace generated, the ORL will be calculated as the area under the curve. This method willhave an accuracy of ±2 dB. The main advantage when using an OTDR is to display any high reflective points that needto be fixed. It could be a bad splice or a dirty connector.

4.4.4 ORL measurement procedure using an OTDRTo perform a complete measurement with an OTDR, it is always recommended to use a pulse suppressor box (PSB) atthe connector entrance and at the end of the DUT. The PSB should be the same type of fiber used in the network toavoid mode field diameter (MFD) mismatch. All connectors on the pulse suppressor box should be clean and show nosign of damage. Figure 4-11 shows a test setup for measuring the ORL and the optical loss from the ONT to the OLT.

Figure 4-10. ORL results

Poor ORL value (based on 28 dB specification)

Good ORL values


Since after the splitter there isalways a recovery zone (deadzone) and also the splitterattenuates the ORL thatcomes from the OLT sidewhen testing from the ONT, itis recommended to measurethe ORL from the OLT up tothe splitter as well. A pass/failthreshold for ORL andreflectance could be set in theOTDR setup to quicklyhighlight high ORL and themost contributor of it. TheFigure 4-12 illustrates highreflective points at event 2 thatfailed the limit and should befixed.

Figure 4-11. ORL measurement for the ONT to the OLT.

CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

FDHSplitter1 X N

Patch Panel

Drop Terminal

Drop Terminal

Drop Distribution FiberONT

ONT

ONT

ONT


4.5 Test 2: Bidirectional Loss TestingOptical loss is defined as the difference in powerlevel between the transmitting source and thereceiving power meter. The total opticalsystem/link loss is the sum of the insertion loss(IL) of the OLT connector, WDM coupler, splices,fiber attenuation, splitter, ONT connector and anyfaulty connector matings. IL is the loss of opticalenergy resulting from the insertion of acomponent or device in an optical path.

When the network is designed, a loss budget isestablished in accordance with standard values.This is a detailed analysis to ensure that thereceiver will receive the level of power required forerror-free transmission. The loss budget takes intoaccount the transmitter power and the receiversensitivity, as well as the expected loss of everyoptical component in the network. The loss budgetrequirement for the PON, based on ITU-T, is shown in Table 4-2.

Figure 4-12. An event that failed the reflective limit


Table 4-2. PON loss budget table

ORL (dB)

Attenuation 2 (dB)

Class A Class B Class B+ Class CITU-T Rec.

IEEE802.3ah

1000BASE-PX

Min. Max. Min. Max. Min. Max. Min. Max. Min. Max.10 km 20 km

Min. Max. Min. Max.

GPON >32 5 20 10 25

See Table 4-3

15 30 G.984.2

BPON 32 5 20 10 25 15 30

G.983.1

G.9821

G.983.3

EPON 20 155 19.5 10 23.5

20 20 24 24

D

U

BPONClass B+

Down UpStandards

Min. Max. Min. Max.

Bit rate (Mbit/s) 622.08 155.52

G.983 seriesVideo overlay (dB) 9 27 13 29

IPTV (dB) 10 28 10 28

Table 4-3. Class B+ loss budget table


The splitters in a PON cause an inherent loss because the input power is divided between several outputs. Splitter lossdepends on the split ratio and is approximately 3 dB for a 1:2 splitter, increasing by 3 dB each time the number ofoutputs is doubled. A 1:32 splitter has a splitter loss of at least 15 dB. This loss is seen for both downstream andupstream 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-lineareffects 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 nomargin. The worst loss comes from the splitter (68%), and its loss would need to be improved, otherwise class Ctransmission would be required to guarantee the loss margin.

4.5.1 Loss testing using an OPMand an OLTSLoss can be measured using a separatesource and an optical power meter (OPM).A basic OLTS consists of a light sourceand an OPM, while an advanced OLTSconsists of a light source and OPMcombined in one unit and is particularlyuseful for bidirectional testing, automaticreferencing and results analysis. Some ofthe more advanced OLTS units canperform automatic bidirectional end-to-end loss and ORL tests together, alsoproviding an estimate of the link distance.

Loss (dB) Number/Length Total Loss (dB)Splitter (1:32) ~ 16-17 1 17WDM coupler (1:2) ~ 0.7-1.0 1 1Splice (fused) ~ 0.02-0.05 4 0.2Connector (APC) ~ 0.2 2 0.4Fiber G.652C ~ 0.35/km 18.2 km 6.4Worst case: 1310 nmTotal loss (dB)1310 nm 25.0Minimum budget Maximim of loss class class B

Table 4-4. A typical loss budget scenario (worst case: 18.2 km maximum)


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 distancecoverage

• 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 legacyfibers showing larger attenuation compared to the more recent vintages. Testing at the three service wavelengthsensures 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 Sethttp://documents.EXFO.com/appnotes/anote021-ang.pdf

• Accurate Loss Testing Made Easyhttp://documents.EXFO.com/appnotes/pnote006-ang.pdf

• Loss Measurement in Fiber-Optic Networks http://documents.EXFO.com/appnotes/pnote007-ang.pdf


4.5.2 Loss measurement procedure using an OLTSTo perform automatic loss testing using two OLTS units,four steps are usually required (refer to the user guidesupplied with the instrument for detailed information):

• Offset nulling (if required by the instruments)compensates for detector noise and internal offsets—some test units do not require this step

• Test setup (on both instruments) allows for theselection of the wavelength(s) and other testparameters

• Referencing (on both instruments) is necessary tomeasure loss through the fiber only, and not through thetest jumpers and accessories—some units automaticallyperform this step

• 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 isperformed 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 detectorport of unit B and the source of unit B to the detector port of unit A.

Figure 4-13. FOT-930 loss results

Bad lossresults

Good lossresults


Once both OLTS units have been referenced, the jumper on eachOLTS is disconnected from the detector port and connected to thefiber under test (FUT). The test is initiated on one OLTS. The sourceof this OLTS sends light through the link. The other OLTS measuresthe received power values and communicates this information to theinitiating instrument, which compares the quantity of light receivedwith the reference measurement. The difference between the twomeasurements corresponds to the average link loss.

4.5.3 Loss measurement using an OTDRDuring PON installation, it is important to ensure that each cablesection meets or exceeds the cable specifications. This can best beaccomplished by using an OTDR. Unlike an OLTS, whichcharacterizes the overall loss of an entire link using two instruments,an OTDR provides a detailed map of all of the section losses (seeFigure 4-15), allowing users to locate and characterize everyindividual element in the link, including connectors, splices, splitters,couplers and faults.

An OTDR operates by sending a high-power pulse of light down thefiber and measuring the light reflected back. Every event in the link(i.e., each optical component and optical fault) causes a reflection oran optical loss, or both. Fiber ends and fiber breaks, as well asconnectors and other components, each reflect a small part of thepulse back to the OTDR. The OTDR uses the time it takes individualreflections to return to determine the distance of each event.

Reference Patchcord

Adapter

Figure 4-15. Cable section mapping from splitter input toWDM coupler output

Reflection

Slope showsfiber attenuation

Loss

Pow

er (

dB)

Figure 4-14. OLTS loopback referencing


Optical fibers uniformly backscatter a small portion of the light over their entirelength. The OTDR measures this backscattered light to determine theattenuation of the fiber. Sudden reductions in the level of backscattered lightcorrespond to optical losses due to splices or other events. For instance, thetypical attenuation of the G.652.C fibers can be measured over the ranges ofwavelengths used in the PON, typically:

• 0.33 dB/km at 1310 nm (0.35 dB/km for worst case)



Larger spectral attenuations may be observed in old G.652 fibers.

The faults that can be detected by the OTDR include misalignments and mismatches, angular faults, dirt on connectorferrules, fiber breaks and macrobends. Macrobends are unwanted events that are caused when a fiber is bent tighterthan 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 atlower ones (1310 nm). The best OTDR wavelength available for macrobending detection is 1625 nm (the longer thewavelength, 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 moreaccurate results since the loss values measured in each direction can be averaged.

Figure 4-16. EXFO’s FTB-7400E OTDRhoused in the FTB-200 Compact Platform


Another important consideration when using an OTDR is the dead-zone phenomenon. Due to the fact that the detectorin the OTDR is extremely sensitive, it may become saturated by strong reflections, such as from the OTDR outputconnector and from the first event (connector) in the network. Often, the longest dead zone occurs at the firstconnection (the OTDR bulkhead connector). Since it is impossible to measure loss within a dead zone, loss due tosplices 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 PSBcontains a length of fiber-optic cable that allows the first connector, as well as events hidden by the dead zone, to beincluded 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 theconnector loss.

For PON testing, the OTDR should be capable of testing at eitherthree wavelengths (1310, 1490 and 1550 nm). In many cases,testing at 1550 nm is considered adequate to cover the 1490 nmregion at the same time. It is generally agreed that the fiberattenuation at 1490 nm is approximately 0.02 dB greater than at1550 nm, which for a maximum of 20 km adds 0.4 dB of totalattenuation. This is usually true for very recent vintage fiber (late’90s and younger), especially for the G.652.C. However, this may bequestionable for older vintage fiber (early ’90s and older) whenG.652.C did not yet exist and when little interest was placed on thewater peak (E-band).

Figure 4.17. FTTx PON OTDR trace


For testing long fibers or lossy components, high dynamic range is necessary, whereas when characterizing a discreteevent, a short pulse is often required. These two features contradict each other: a longer pulse will provide a higherdynamic 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 manyaspects 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). Animportant question that arises is: What will happen when the signal crosses the splitter? With a standard OTDR, it maynot have enough dynamic range to see after the splitter—and increasing the pulse width it will not have enoughresolution.

The OTDR analysis software must be well-designed tothoroughly locate all possible types of events, such asreflections caused by connectors, fiber breaks or fiber ends,as well as losses caused by splices or macrobends in additionto gains caused by imperfect core alignments or diameterdifferences (delta variations in mode-field diameter). A good-quality OTDR should be able to clearly point out all the typesof events on the trace; to make them easily identifiable to theuser and to list the events in an events table.

It is important to select an option that provides a well-designed, easy-to-use interface and includes features suchas signal averaging, report generation and printing, as well asan automatic mode of operation. Some OTDRs also include abuilt-in visual fault locator (VFL). Figure 4-18. Standard OTDR testing through a splitter demonstrating

lack of resolution


For further information on using an OTDR, refer to the following articles on our website (www.EXFO.com):

• Bidirectional OTDR Testing: Multimode vs. Singlemode Fibershttp://documents.EXFO.com/appnotes/anote043-ang.pdf

• Optimizing OTDR Measurement Parametershttp://documents.EXFO.com/appnotes/anote076-ang.pdf

• Fiber-Optic Testing Challenges in Point-to-Multipoint PON Testinghttp://documents.EXFO.com/appnotes/anote110-ang.pdf

• An Innovative Solution for In-service Troubleshooting on Live FTTH Networkshttp://documents.EXFO.com/appnotes/anote130-ang.pdf

• Selecting the Right OTDRhttp://documents.EXFO.com/appnotes/anote142-ang.pdf

• OTDR PON Testing: The Challenges—The Solutionhttp://documents.EXFO.com/appnotes/anote201-ang.pdf


4.6. OTDR Settings Before using an OTDR, it is important to understand the test parameters to be able to test them correctly. Althoughmany OTDRs have an Auto mode in which the instrument attempts to determine the optimal settings for the link undertest, in some situations, it may be necessary to manually set the parameters in order to obtain the desired results. Whentesting at several different wavelengths, the same settings for all wavelengths or different settings for each individualwavelength can be used. In addition, there are usually options for storing test results in a database and for printingreports. 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 travelsfurther down the fiber and improves the signal-to-noise ratio (SNR) but results in less resolution, making it moredifficult to separate closely spaced events. A longer pulse also results in longer dead zones. In contrast, a shorterpulse width provides higher resolution and shorter dead zones, but less distance range and lower SNR. Generally, itis preferable to select the shortest possible pulse width, enabling to see everything and then proceed to make furtheradjustments for optimization.

Note that when testing downstream in an FTTx network, the optical power of the OTDR pulse must be large enoughto 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 theacquisition time increases, more of the noise is averaged out; this averaging increases the SNR and the ability forthe 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 beused (e.g., 10 s). To fully characterize a link with optimal precision and to make sure the end-to-end loss budget isrespected, a longer acquisition time (45 s to 3 min) is preferable.


• Pass/warning/fail criteria: Some OTDRs can display a message at the end of an analysis to inform the user if oneor more events exceed a preset threshold. Separate warning and fail thresholds can be set for each type ofmeasurement (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 ProcedureDuring installation, OTDR testing should be performed after installation of each segment of the network. Figures 4-19and 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 witha slightly different geometry, the loss found with an OTDR varies for different testing directions. Averaging the lossesfrom 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 manydistribution fibers are being tested, the reflection of each of the different fibers will be combined and the interpretationof 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


CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

FDHSplitter1 X N

Patch Panel

Drop Terminal

Drop Terminal


ONT

CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

Drop Terminal

Drop Terminal

Drop

Drop Terminal

Drop Terminal

Drop


ONT

Figure 4-20. Testing from the splitter output to the CO

CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

FDHSplitter1 X N

Patch Panel

Drop Terminal

Drop Terminal


ONT

CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

DropONT

ONT

Figure 4-19. Testing from an ONT or drop terminal to the CO


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.

5. Service Activation Testing


5. Service Activation TestingThe 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 isonly done during the initial activation because it cannot be repeated without interrupting service for the entire networkonce the network has been connected. To perform this measurement, disconnect the feeder fiber and measure thepower 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 powerat each individual wavelength, one wavelength at a time

• A wavelength-demux PON powermeter measures the power ofeach wavelength simultaneously:power thresholds can be set inorder to provide pass, warning orfail status for each wavelength

After reconnecting the feederfiber, perform a similar test at theFDH, measuring the power ateach splitter output.

CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

FDHSplitter1 X N

Patch Panel

DropTerminal

Drop

DropTerminal

DistributionFiber

ONT

ONT

ONT

ONT

Figure 5-1. PON power meter connected between the drop and the ONT


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 pass-through device. Another method is to use an OPM and filters; however, this method does not allow measurement of theupstream 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 ofinstrument 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 thetraffic bursts in order to provide accurate measurements.

5.3 Multiple Testing LocationsIt is important to keep in mind that FTTH networks link one location to multiple locations, also called point-to-multipointnetworks (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 defectivecomponents before activating a customer’s service. Since FTTH network problems are often caused by dirty ordamaged connectors, component inspection greatly reduces troubleshooting, as power levels are verified for eachnetwork section. It is also highly recommended to inspect each connection point using a fiber inspection probe, suchas 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):


5.4 Storing Data during Service ActivationData collected during activation must be classified, included in a report and can also beincluded in a data base for future reference.

An advanced PON power meter will feature a PON adapted storage interface whichallows saving results per OLT or central office (CO), per ONT and even per test location.This greatly facilitates data management and reporting.

CO

Patch Panel

Voice

IPTV

RF

Data

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

FDHSplitter1 X N

Patch Panel

Drop Terminal

Drop Terminal


ONT

ONT

ONT

12 3

Figure 5.2. PON power meter measurements at different locations

Figure 5.3. The PPM-350C’s PON-adapted graphical user interface—storage screen


The downstream power at 1550 and1490 nm must meet the minimumONT receiver sensitivity (depending onthe PON class). The upstream powershould correspond to the ONTspecifications. If the optical power levelis insufficient, refer to Chapter 6 andperform the troubleshooting steps.Perform other troubleshooting steps asnecessary to correct the problem.Similarly, the upstream power at 1310 nmmust meet minimum criteria to beproperly detected at the OLT. Knowingthe worst-case optical power budget, itis simple to define a minimum opticalpower value that the 1310 nm signalmust have at the ONT output.

When all problems have been corrected and the measured power level at the drop is sufficient, connect the drop directlyto the ONT.

Note: It is crucial to understand that the 1310 nm signal transmitted upstream by the ONT is, by nature, a burst andis 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 • PPM-350 Measurement Techniqueshttp://documents.exfo.com/appnotes/anote207-ang.pdf http://documents.exfo.com/appnotes/anote131-ang.pdf

Table 5-1. PON optical loss budget requirements for single-fiber topology (Rx max. power sensitivityis called “overload”)

Bit Rate Class 1490 nm Power (dBm) Standards(Mbit/s) OLT Tx ONT Rx

Min Max Sens. Over155.52 A -6 0 -27 -5 G.983/G.984 series

B -4 +2 -30 -8C -2 +4 -33 -11

622.08 A -6 -1 -27 -6 G.983/G.984 seriesB -1 +4 -27 -6C -1 +4 -32 -11

1000 (nominal) -1 +4 -24 EPON: 1000BASE-PX10-1 +4 -27 EPON: 1000BASE-PX20

1244.16 A -3/-2 +2/+3 -24/-23 -3/-8 G.983/G.983 seriesB -2 +3 -28 -7/-13C +2 +7 -29 -8/-14

2488.32 A G.984 seriesBC

6. Network Troubleshooting


6. Network TroubleshootingTroubleshooting a PON first involves locating and identifying the source of an optical problem in what may be a complexoptical network topology that includes several splitters, fibers and ONTs. Figure 6-1 shows a multisplitter topologynetwork with multiple splitters. The numbers indicate the different zones where a problem may be located. If a breakoccurs in the cable between the OLT and adownstream splitter, all ONTs downstreamfrom that splitter will be affected; however, ifa problem such as macrobending or dirtyconnectors causes optical power to be lostsomewhere in the network, only a number ofdownstream ONTs may be affected. Sincethe attenuation in fiber optic cables isproportional to length, distant ONTs receive aweaker downstream optical signal thancloser ones. The upstream optical signalsreceived at the CO from the more distantONTs are also weaker and the OLT willdetect such decreased performance.

Problems that may occur in an FTTx network

Neighborhood FDH

Splitter

.........

........

FDHCO

Zone

-1

Zone

-2

Zone

-4

Zone

-6

Zone

-3

Zone

-5

Zone

-7

OLTWDM

CouplerOpticalVideo

Transmitter

1x4

.........

1x8

.........

1x8

ONT

ONT

ONT

ONT

Figure 6-1. Troubleshooting zones in a typical FTTx network


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 todirty/damaged/misaligned connectors or breaks/macrobends in the fiber-optical cable. These will affect one, some orall 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 thatenables 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 fortesting at 1625 or 1650 nm and incorporate a filter that rejects all unwanted signals (1310, 1490 and 1550 nm) that couldcontaminate the OTDR measurement. Only the OTDR signal at 1625 or 1650 nm is allowed to pass through thefilter, 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.


A PON-optimized OTDR does not interfere with the CO’s transmitter lasers because the 1650 nm wavelength complieswith the ITU-T L.41 Recommendation (Maintenance wavelength on fibers carrying signals). This ITU-T recommendationsuggests a 100 nm difference between the OTDR wavelength used for in-service maintenance and the closesttransmission wavelength, in this case, 1550 nm. The addition of a broadband filter, acting as a 1625 or 1650 nm testingport at the CO’s WDM coupler, may also be beneficial. As a result, the quality of service provided to other subscribersserviced by the same 1xN splitter is not affected. Armed with this technology, the technician can connect the OTDR’s1625 or 1650 nm port to the ONT and send the signal toward the CO. If a 1625 or 1650 nm testing port is added tothe CO, it is also possible to perform tests from the CO down to the ONT, but a 1625 or 1650 nm filter may be neededat each ONT.

For further information on using an OTDR for troubleshooting a PON network, refer to the following articles on ourwebsite (www.EXFO.com):

• An Innovative Solution for In-service Troubleshooting on Live FTTH Networkshttp://documents.EXFO.com/appnotes/anote130-ang.pdf

• OTDR PON Testing: The Challenges—The Solutionhttp://documents.EXFO.com/appnotes/anote201-ang.pdf


Fiber inspection probe: A fiber inspection probe (FIP) is the most versatileway 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 connectorsas it relies on an LCD display or instrument screen to display the connectorimage as opposed to a microscope that uses lenses. Some FIPs also allowtaking pictures of connector ports for documentation.

Note on security:

In PON troubleshooting, if one customeris activated, the whole network receivesthe broadcasted DATA signal at 1490 nmor RF video signal (if present) at 1550 nmas the network is passive. For this reason,it is highly recommended to use an FIPinstead of a microscope whentroubleshooting a customer on an activenetwork.

Figure 6-2: OLTS with a fiber inspection probeconnection port

CO

OLTWDM

Coupler

OpticalVideo

Transmitter

FDHNeighborhood FDH

Splitter1 X N ONT

ONT

ONT

ONT

Figure 6-3.


Problem Possible Cause Troubleshooting Steps

One ONT is Dirty/damaged connectors or At the end of the drop:malfunctioning; excessive macrobends after � Measure the optical poweroptical power level last splitter � Inspect the connectorsat ONT is low ONT failure At the drop terminal:

� Measure the optical power� Inspect the connectorsAt the splitter output:� Measure the optical power� Inspect the connectors

One ONT is not working; Fiber break after last splitter � Measure optical power at ONT to confirm that there is no signalno optical power (in distribution fiber or drop cable) � Measure optical fiber at drop terminal

ONT failure If signal is present: Problem is in drop cable� Test drop cable from ONT or from drop terminal using VFL or OTDR

If signal is not present: Problem is in distribution fiber� Test distribution fiber from drop terminal using OTDR

One ONT is malfunctioning; ONT hardware problem � Refer to ONT manufacturer’s troubleshooting procedurepower level at ONT is OK

The following table lists problems, their possible causes and the troubleshooting steps to take:

Table 6-1. Troubleshooting


Problem Possible Cause Troubleshooting Steps

Some or all ONTs connected Dirty/damaged connectors or At the splitter output:to one splitter are macrobends before splitter � Measure the optical powermalfunctioning; � Inspect the connectorspower level at ONTs is low Check for macrobends (inside and outside the FDH)

At the splitter input:� Measure the optical power� Inspect the connectors

All ONTs connected to one Fiber break before last splitter � Test feeder fiber (or fiber between splitters in the case of multisplitter splitter are not working; link) with OTDR from ONT, drop terminal or splitterno optical power

All ONTs are not working; Break in feeder fiber or � Test feeder fiber with OTDR from the FDH or the COno optical power problem at CO � Measure OLT output power

� Measure power of video signal before WDM coupler� Measure WDM coupler output power� Check equipment at CO

BER increase Insufficient power at ONT or � Perform steps above as necessaryONT hardware problem � Refer to ONT manufacturer’s troubleshooting procedure

Intermittent problem ONT hardware problem � Refer to ONT manufacturer’s troubleshooting procedure

Table 6-1. Troubleshooting (continued)


Figure 6-4. Using a PON power meter for troubleshooting various points in the network

CO

Patch Panel

VoiceData

OLT

EDFA

WDM Coupler

OpticalVideo

Transmitter

FDHSplitter1 X N

Patch Panel

Drop Terminal

Drop Terminal


ONT

ONT

ONT


7. Abbreviations and AcronymsADS Additional digital serviceADSL Asymmetric digital subscriber line (copper based)APC Angled physical contact/angled polished

connectorAPD Avalanche photo diode (detector)ATM Asynchronous transfer mode protocolBER Bit error rate (ITU-T uses bit error ratio)BLEC Building local exchange carrierBPON Broadband passive optical networkCD Chromatic dispersionCDMA Collision detected multiple accessCLEC Competitive local exchange carrierCO Central officeCVD Chemical vapor despositionCWDM Coarse wavelength-division multiplexingDBS Direct broadcast serviceDFB Distributed-feedback (laser)DSL Digital subscriber line (copper based)DSLAM Digital subscriber line access multiplexerDUT Device under testDWDM Dense wavelength-division multiplexing

EDFA Erbium-doped fiber amplifierEFM Ethernet in the first mileEFMA Ethernet-in-the-first-mile allianceEPON Ethernet-ready passive optical networkFBT Fused biconic taper (fiber coupler/splitter)FCC Federal communications commission (US)FDH Fiber Distribution HubFDT Fiber Distribution TerminalFEC Forward Error CorrectionFC Fiber CollectorFO Fiber-opticFP Fabry-Perot (laser)FSAN Full-service access networkFTTB Fiber-to-the-buildingFTTC Fiber-to-the-curbFTTCab Fiber-to-the-cabinetFTTH Fiber-to-the-homeFTTN Fiber-to-the-nodeFTTP Fiber-to-the-premisesFTTx Fiber-to-the-x, where x = (H)ome, (C)urb,

(B)uilding, (N)ode, (P)remises, etc.


FUT Fiber under testGEM GPON encapsulation modeGPON Gigabit-capable passive optical networkHDD Horizontal direct drillingHDSL High-bit-rate digital subscriber line

(copper based)HDTV High-definition televisionHFC Hybrid fiber coaxial transmissionsIEC International electrotechnical commissionIEEE Institute of electrical and electronic engineersILEC Incumbent local exchange carrierIP Internet protocolIPTV Internet protocol television ITU International telecommunication unionITU-T International telecommunication union—

telecommunications standardization sectorwavelength

LFD Live fiber detectorMAN Metropolitan area networkMDU Multi-Dwelling UnitMFD Mode-field diameterMLM Multilongitudinal mode (Laser)

MM MultimodeMMF Multimode fiberMWM Multiwavelength meterNF Noise figure (noise from an optical amplifier in dB)OC Optical carrier (transport rate)ODN Optical distribution networkODU Optical distribution unitOLT Optical line terminal/terminationOLTS Optical loss test setONT Optical network terminal/terminationONU Optical network unit (non-transmitting ONT)OPM Optical power meterORL Optical return lossOSA Optical spectrum analyzerOSC Optical service channelOSNR Optical signal-to-noise ratioOSP Outside plantOTDR Optical time-domain reflectometerP2MP Point-to-multipointP2P Point-to-pointPBX Private branch exchange


PC Polished connectorPIN Positive-insulator-negative (detector)PLC Planar lightwave (or lightguide) circuitPMD Polarization mode dispersion or physical

medium dependentPON Passive optical networkPOTS Plain old telephone servicePSB Pulse suppressor boxPSTN Public switched telephone networkQoS Quality of serviceRBOC Regional Bell operating companyRec ITU-T RecommendationRLEC Rural local exchange carrierRT Remote terminalRx ReceiverSC Supervisory channel or service channelSDH Synchronous digital hierarchySM SinglemodeSMF Singlemode fiberSNR Signal-to-noise ratioSONET Synchronous optical network

STM Synchronous transfer mode (SDH transfer rate)

TDM Time-division multiplexingTDMA Time-division multiple accessTIA Telecommunications Industry AssociationTx TransmitterUPC Ultra-polished connectorVDSL Very-high-speed digital subscriber line

(copper based)VFL Visual fault locatorVOD Video-on-demandVoIP Voice over Internet protocolWDM Wavelength-division multiplexingxDSL Generic digital subscriber line (copper based)

8. List of ITU-T PON RecommendationsFiber RecommendationsG.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 caG.652: Characteristics of a single-mode optical fibre and cableG.653: Characteristics of a dispersion-shifted single-mode optical fibre and cableG.654: Characteristics of a cut-off shifted single-mode optical fibre and cableG.655: Characteristics of a non-zero dispersion-shifted single-mode optical fibre and cableG.656: Characteristics of a fibre and cable with non-zero dispersion for wideband optical transportG.657: Characteristics of a bending loss insensitive single mode optical fibre and cable for the access network

Component and sub-system RecommendationsG.671: Transmission characteristics of optical components and subsystems

PON System and network RecommendationsG.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-PONG.983.3: A broadband optical access system with increased service capability by wavelength allocationG.983.4: A broadband optical access system with increased service capability using dynamic bandwidth assignmentG.983.5: A broadband optical access system with enhanced survivabilityG.983.9: B-PON ONT management and control interface (MCI) support for wireless local-area network interfacesG.983.10: B-PON ONT management and control interface (OMCI) support for digital subscriber line interfaces



G.984 seriesG.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 exchangebetween systems—local and metropolitan area networks. Specific requirements Part 3: Carrier Sense Multiple Accesswith Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications Amendment: Media AccessControl Parameters, Physical Layers and Management Parameters for Subscriber Access Networks

9. Appendix


9. AppendixPON Classification1. ONU1.1 ONU installed inside premises1.2 ONU installed outside premises

2. Drop terminals/drop cables2.1 ODN installed using drop terminal and drop cables2.2 ODN installed without drop terminal and drop cables (F2 directly to ONU)

3. Splitter3.1 ODN using single splitter with maximum split ratio3.2 ODN using multistage splitter with various split ratios

4. F14.1 F1 with no redundancy4.2 F1 using redundancy

5. Video5.1 PON without video distribution5.2 PON including video distribution

5.2.1 PON with overlaid analog RF video5.2.2 PON with digital IPTV

6. Monitoring6.1 PON without optical/physical monitoring6.2 PON with optical/physical monitoring


Notes

For details on any of our products andservices, or to download technical andapplication notes, visit our website atwww.EXFO.com.

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