Maintenance & Troubleshooting of a PON Network with an OTDR
Contents
1. OTDR tool the correct pulse width and the best location to start troubleshooting OTDR configuration should be set according to the equipment being qualified and the distance to cover Consider each case from the scenarios presented in Figure 7 To avoid complexity this document only analyzes the cases where connectors are only available at the ONT OLTs Case 1 Troubleshooting of the Distribution Fiber Simple PON Only one subscriber affected Consider that no connectors are available at the splitter see Figure 7 Test 3 Case Test OTDR What Must Comment PulseWidth Specific OTDR Location Direction be Seen to Use Case 1 Customer s Upstream Distribution Testing through Short pulse In service OTDR One Home fiber up to the splitter 3 to 30 ns customer Disconnect the closest splitter is not required down the ONT as the issue is only on the distribution fiber side ONT or ONU Splitter A 5038 99m 2 520dB B 5038 99m 2 520dB an Rison m 0 000dB A A B 0 00m Ba 04 0 328dBkm l 57 2533 54m 0 50348 1 1 1 1 0 1 2 3 4 5 Km The OTDR trace must clearly ween show all events until the closest splitter Case 1 A Simple PON Only one customer affected Test direction upstream No need to test beyond the splitter Test the distribution Fiber from Customer 2 up to the closest splitter Figure 10 OTDR is Shot Upstream and Trace only Matters up to the S2. Application Note lt gt JDSU Maintenance amp Troubleshooting of a PON Network with an OTDR Troubleshooting a faulty passive optical point to multipoint network PON can be more complex than a point to point network This application note looks at the use of non intrusive or active fiber testing for troubleshooting PON networks Point to Point FT Tx Network When a failure occurs on a point to point FTTx network the network completely shuts down It is then easy to disconnect the fiber without further affecting the customer issue To troubleshoot and fix FT Tx network problems an optical time domain reflectometry OTDR test can be performed with any test wavelength such as 1310 or 1550 nm as the transmission signals are shut down CO ONT or DSLAM Switch or Final OLT customer B Figure 1 FTTx Case Point to Point FTTH Network Point to Multipoint FTTH Network PON Topology Troubleshooting a point to multipoint fiber to the home FTTH network also defined as a PON net work differs significantly The International Telecommunications Union ITU T and Institute of Electrical and Electronic Engineers IEEE have created several standards for optical access systems based on PON architecture G 982 G 983 or G 984 for ITU and 802 3ah or 802 3av for IEEE As Figure 2 shows a PON network consists of one optical line terminal OLT connected via a splitter to multiple optical network terminal
3. DR 4 Recommended Steps for Locating Faults Despite the fact companies with diverse fiber networks have their own methods and procedures most of them optimize their fault location process to reduce the number of truck rolls The schematic in Figure 7 offers a complete view of Allofthe possible fault locations depending on how many customers are affected The best location to shoot an OTDR while minimizing truck rolls Whether or not a specific in service OTDR device should be used Which scenario What type of FFTx Network is it Point to Point FTTx Network ONT or ONU PON Network Multi Point FTTH network How many customers are affected Possible faulty elements The OLT The distribution fiber The ONT The customer home wiring Second step analysis The distribution fiber between the customer amp the closest splitter The ONT The customer home wiring See Figure 4 More than one Are affected customers connected to the same first splitter Yes wether cascaded splitters or not Figure 7 Schematic Summary e eee The last splitter The fiber link between the cascaded splitters See Figure 5 The OLT itself The feeder part of the fiber network The first splitter See Figure 6 Are connectors availabe at the last splitter Assuming problem could not be solved by phone Are conne
4. Possible Faults When Only One Subscriber is Affected Final customer 2 Last splitter Final customer 3 PON Case 2 Cascaded PON and all Affected Customers are Connected to the Same Splitter When all customers connected to the same splitter cannot receive service but others connected to the same OLT can the cause may be because of one of the following see Figure 5 Fault at the last splitter Fault in the fiber link between the cascaded splitters ONT or ONU First splitter Final customer 1 f D Final i customer Last splitter 2 f D Final customer 3 Figure 5 PON Case 2 Cascaded PON with Affected Subscribers Connected to Last Splitter Application Note Maintenance amp Troubleshooting of a PON Network with an OTDR PON Case 3 All Customers are Affected at the OLT level Whether or not the PON is cascaded all customers dependant on the same OLT may be affected If all cus tomers are affected the cause may be from of the following Faultin the splitter closest to the OLT Fault in the feeder fiber cable of the fiber network Fault in the OLT equipment ONT or ONU Final customer 1 First splitter OLT Final customer 2 Final customer 3 Figure 6 PON Case 3 All Subscribers are Affected All Connected to the First Splitter Other Variable Splices or Connectors at
5. Strategic Places If connectors are available at the splitters terminals or drops isolating part of the faulty network easier Inspecting connectors and taking OTDR measurements using 1310 1550 nm wavelengths are often per formed on network sections that are out of service In service testing test on a network carrying traffic is needed mostly when the entire network is spliced and when some but not all customers are affected Constraints of In service Testing Measurements In order to troubleshoot PON networks in service two dedicated tools are available PON power meter In service 1625 or 1650 nm OTDR Traffic wavelengths are typically 1310 1490 or 1310 1490 1550 nm A PON power meter is normally employed to verify that the signal is transmitted correctly to and from the ONT A PON meter measures the power levels of all the signals and can then discriminate whether the issue comes from the customer s ONT or from the network The use of a classical OTDR with 1310 or 1550 nm test wavelengths would interfere with the traffic signals and disturb the traffic At the same time the traffic signals could also disturb the receiver of the OTDR making it difficult to interpret OTDR traces Because of these mutual disturbances classical OTDRs cannot be used and specific in service OTDRs are required see section on Specific In service Portable OTDR Device Application Note Maintenance amp Troubleshooting of a PON Network with an OT
6. ctors availabe at the last splitter Shoot an OTDR from the OLT towards the ONT Shoot an OTDR from the last splitter towards the ONT Shoot an OTDR from the OLT towards the first splitter Shoot an OTDR from the ONT up to the closest splitter Shoot an OTDR from the last splitter towards the fist splitter Shoot an OTDR from the ONT towardsthe closest splitter Application Note Maintenance amp Troubleshooting of a PON Network with an OTDR Specific In service Portable OTDR Device The in service OTDR was designed specifically for testing live fiber networks This dedicated device uses an out of band wavelength test wavelength far away from traffic wavelength to enable OTDR testing without disturbing either the network transmitters or the receivers JDSU first developed this particular OTDR a few years ago allowing dark fiber providers to perform in service monitoring on metropolitan and long distance networks In this case a wavelength dense mul tiplexer WDM is required to connect the OTDR to the network itself while the traffic remains active In the case of a PON network this WDM is no longer needed except for monitoring purposes using a remote fiber test system The PON network is a point to multipoint configuration and the troubleshoot ing test is performed directly from an accessible element ONT or splitter The operator can disconnect the element because service is already of
7. ery first splitter Figure 11 OTDRis Shot Upstream and Trace should Display the Traffic through the Last Splitter up to the First One Application Note Maintenance amp Troubleshooting of a PON Network with an OTDR 8 Case 3 Troubleshooting of the Feeder Whether it is a non cascaded network which is typical in the USA or a cascaded network which is typical in Europe and Asia Pacific information received at the NOC shows that all customers are down As the problem likely comes from the feeder side the most common way to test the faulty network is to shoot an OTDR downstream from the OLT see Figure7 Test 6 Case Test OTDR What Must Comment PulseWidth Specific OTDR Location Direction be Seen to Use Case 3 OLT Downstream Feeder Testing through Short pulse Unnecessary All the splitter is 3 to 30 ns customers unnecessary are down ONT or ONU Final customer 1 First splitter 1625nm 10ns 1 44 Fiber044_620E A 0 00m 20 782dB_ _B 2431 98m 20 782dB AB at 98m 0 000dB km 0 000d B 29 68dB 2 1007 831 No need to test The OTDR trace must clearly Test the feeder j beyond the first show all events down to the first splitter up to the splitter splitter Figure 12 OTDR is Shot Downstream and Trace should Display the Traffic Down to the First Splitter Application Note Maintenance amp Troubleshooting of a PON Network with an OTDR 9 Troubleshooting the Dis
8. f downstream toward the customer First the in service OTDR must not disturb the other customers while shooting the OTDR test wave length upstream toward the OLT which is most likely the case as OLTs reject signals above 1625 nm based on ITU T recommendations Second the traffic signals that the OTDR receives will be rejected to obtain accurate OTDR traces The specific long pass filter used to protect the OTDR diode can be added either via a jumper between the OTDR and the network or built into the OTDR Test wavelength OTDR with built in LP filter Multiplexer Signals Link 1 Final gh ati 3 amp OTDR Filter Figure 8 OTDR Insertion for In service Monitoring Figure 9 OTDR Insertion for FTTH Troubleshooting at a Customer Location ONT is disconnected Most equipment providers enable the use of the 1625 nm wavelength for safe testing Some countries such as Japan are nevertheless pushing the 1650 nm wavelength as reflected in the ITU T L 41 recommen dation which provides maintenance wavelengths on fiber carrying signals The 1650 nm wavelength is preferred based on the design of the filters and also because it is further away from the traffic signals cur rent and future PON technologies Application Note Maintenance amp Troubleshooting of a PON Network with an OTDR O Making the Right Testing Decisions To optimize maintenance costs and time it is essential to select the right
9. oducts communications test measurement products details triple play service deployment html ae Application Note Maintenance amp Troubleshooting of a PON Network with an OTDR Test amp Measurement Regional Sales WEBSITE www jdsu com test ASIA PACIFIC EMEA TEL 852 2892 0990 TEL 49 7121 86 2222 FAX 852 2892 0770 FAX 49 7121 86 1222 30162937 000 0110 LATIN AMERICA TEL 1 954 688 5660 FAX 1 954 345 4668 NORTH AMERICA TEL 1 866 228 3762 FAX 1 301 353 9216 Product specifications and descriptions in this document subject to change without notice 2010 JDS Uniphase Corporation PONOTDR AN FOP TM AE January 2010
10. onally or bidirectionally OTDR For this phase JDSU recommends the SmartClass Family and or the T BERD MTS 4000 or 6000 to optimize this process d B j IL A N H e ie T Figure 14 Recommended tools a SmartClass Family optical handheld or a T BERD MTS 4000 or T BERD MTS 6000 equipped with an OTDR module Turn up Phase The following equipments should be used in conjunction A PON power meter 1310 1490 1490 1550 or 1310 1490 1550 nm IP testers voice data video and coaxial testers For this phase JDSU recommends our SmartClass Family in particular the PON dedicated OLP 57 the T BERD MTS 4000 and the HST 3000 to optimize this process Figure 15 Recommended tools an HST 3000 a SmartClass Family OLP 57 and aT BERD MTS 4000 equipped with a PON power meter Oe eee Application Note Maintenance amp Troubleshooting of a PON Network with an OTDR 1 1 aa Maintenance and Troubleshooting Phase The following equipments should be used in conjunction A PON power meter 1310 1490 1490 1550 or 1310 1490 1550 nm A loss test set or an OTDR IP testers voice data video and coaxial testers For this phase JDSU recommends once more the material described above Figure 16 The Dedicated FTTx T BERD MTS 4000 Platform can be Equipped with a PON an OTDR and Triple Play WiFi Testing Refer to the JDSU Triple Play book for more information which is available on demand at www jdsu com pr
11. plitter Application Note Maintenance amp Troubleshooting of a PON Network with an OTDR a Case 2 Troubleshooting of the Distribution Fiber and the Fiber between the Two Splitters in case of a Cascaded Network A cascaded network with 1x4 or 1x8 splitters is often found in Europe Information received at the network operations center NOC says that all customers linked to the second splitter are down Lets consider the case where no connectors are available at the splitter see Figure 7 Test 5 Case Test OTDR What Must Comment PulseWidth Specific OTDR Location Direction be Seen to Use Case 2 Customer s Upstream Distribution fiber Testing through Medium pulse In service OTDR All customers home and fiber between the closest splitter 100 to 300 ns Short dead zone are down Disconnect the two splitters is required after the the ONT second splitter This case requires viewing the signal after the splitter The OTDR used must be optimized for this applica tion and have the shortest possible dead zone as the splitter typically provides 7 to 10 dB loss ONT or ONU First splitter Final I at j Fiber030_620E an A 0 00m 34 466dB B 0 00m 34 466dB i a ai 0 000dB I A B 0 00m Last splitter 51 22dB Case 2 Cascaded PON Test direction upstream Need to test beyond the closest splitter up to the first splitter Test the distribution Fiber from Customer 2 up to the v
12. s ONTs one for each subscriber up to 64 subscribers Sometimes a second splitter can be connected in cascade to the first splitter as Figure 3 shows to dispatch services to buildings or residential areas CO ONT or ONU CO ONT or ONU Splitter Final Splitter Final customer customer 1 1 Final customer 2 Final customer 3 Final customer 3 pa E ae Final customer 2 ih Figure 2 Simple PON Network Topology Figure 3 Cascaded PON Topology WEBSITE www jdsu com test Application Note Maintenance amp Troubleshooting of a PON Network with an OTDR 2 Using the network monitoring system at the Network Operation Center NOC operators can easily determine which subscribers are affected They can also identify possible fault elements such as how many customers are affected and whether the PON is cascaded The cases below describe each possible scenario PON Case 1 Simple PON Only One Customer is Affected When only one subscriber cannot receive service three potential faults are probable see Figure 4 Fault in the distribution fiber between the customer and the closest splitter Fault in the ONT equipment Fault in the customer s home wiring ONT or ONU ONT or ONU Splitter Final First splitter Final customer customer 1 f i 1 Final OLT customer 2 Final customer 3 Figure 4 PON Case 1
13. tribution Fiber and or the Fiber between Splitters with Alternative OTDR Testing from the OLT OTDR testing directly from the OLT is certainly the preferred choice when a faulty feeder is suspected Case 3 but this method is not recommended in the other cases JOSU OTDR instruments can indeed test through splitters and provide accurate traces Nevertheless complete analysis of the resulting trace requires linking that trace to the exact precisely documented network topology 1550nm 100ns 56 56 030703c 1550100nsnew der A 19919 81m 19 924dB B 0 00m 42 153dB AB 1681881 1 116dBikm i 22 230dB A ee The OTDR trace shows all events including the first splitter 1 8 some end of fibers the second splitter 1 4 Shoot downstream from the feeder All splitters amp ONTs can be seen Figure 13 OTDRis Shot Downstream and Trace Displays Many Events that are Difficult to Identify without Exact Network Topology and corresponding distances Application Note Maintenance amp Troubleshooting of a PON Network with an OTDR 1 0 Complete PON Test Tools This application note focuses primarily on the maintenance and troubleshooting of a PON network using an OTDR Nevertheless other tools can be used during the installation and maintenance trouble shooting stages Installation Phase The following equipment may be used Loss test set provides insertion loss and ORL either unidirecti
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