Implementing a fibre-to-the-home (FTTH) network is an expensive and time-consuming exercise. The networks take months if not years of planning and civil works before they are ready to connect subscribers. During this time, a whole host of issues can affect the physical layer, including cable and ducting issues, blown fibres and challenges caused by an inexperienced testing workforce.
How can providers identify the right testing strategy when it comes to specific FTTH deployment projects? Decisions depend on several factors: network topology, the deployment phase, deadlines, budget, technicians’ level of expertise and contractor outsourcing, to name a few. This article will review some of these factors to help you make the best decisions according to your specific needs.
Topology and technology overview
Many topologies exist in FTTH and each business will deploy the topology that best suits their model and bandwidth. Topologies range typically from single split ratios of 1 x 32 to multiple split ratios of up to 1 x 128 subscribers per PON. All of these can transport GPON, RFoG and next-generation technologies, such as XGS-PON and NG-PON2 where the bandwidth delivery is up to 10Gbps symmetrically.
Test equipment to consider in FTTH deployments
Several test equipment tools are available on the market with each one having their benefits for specific applications and test results required. The below sections list essential pieces of equipment that should be found in a field technician tool kit.
Fibre inspection tool
With faulty connectors being the number one cause of network failures, a fast connector inspection solution can help you save money and give you the assurance that your network is clean. Connectors are the most overlooked aspect of a network, but contamination from a wide range of sources can have a serious impact on network loss and reflectance. Using a fully automated connector inspection solution that will quickly and objectively evaluate a connector health is highly recommended. Make sure the solution is suited for operation in dense and recessed panels and is compatible with all connectors types found in your network, which can be LC/APC or SC/APC typically.
Fig. 1: Single-stage architecture with XGS-PON over G-PON services.
Optical loss test set (OLTS)
An OLTS will validate the link loss budget in a few seconds. Speed of deployment when using an automated OLTS will enhance the turnover of the FTTH network. Drop terminals can be characterised for loss and ORL in less than three seconds, which will confirm continuity, connector cleanliness and overall loss to ensure that the drop cable activation is a simple straightforward process. Make sure to use the proper referencing methods to ensure validity of results. An on-board, step-by-step animated reference assistant on your unit can minimise risk of referencing errors.
Optical time domain reflectometer (OTDR) and intelligent optical link mapper (iOLM)
Using an OTDR to characterise an FTTH network requires expertise to select the correct setting and interpret the network from the drop terminal to the central office/PoP/exchange. In many cases, due to the proximity of optical splitters to one another and other components in the network, it may require more than one measurement to fully characterise the network. This is why an iOLM can become handy in the field to reduce potential human errors by eliminating the need to configure parameters and to interpret complex multiple OTDR traces. Its advanced algorithms dynamically define the testing parameters, as well as the number of acquisitions that best fit the FTTH network under test.
By correlating multiple pulse widths on multiple wavelengths, the iOLM locates all events and identifies faults with maximum resolution at the push of one button. Results are displayed in an icon-based fibre-link view to quickly assess an event pass/fail status per standard selected. The iOLM also delivers an analysis of failed events and suggests solutions to guide technicians in fixing the fault quickly and successfully. An OTDR or iOLM is also frequently used for troubleshooting from the customer side – its ability to find faults in F1 and/or F2 sections, or after the last splitter(s) up to the CO, is very valuable, especially in fully spliced networks.
Visual fault locator (VFL)
A VFL is a quick solution for identifying breaks, bends, faulty connectors or splices, as well as other causes of signal loss. The device visually locates faults by creating a bright red glow at the exact location of the fault. A VFL also helps with fibre identification in an open circuit.
Power meter (PM) or PON power meter
This device is used to diagnose low power as well as locate faulty sections by taking a sequence of measurements at multiple connection points up the network stream. Using a PM that includes a pass-through mode will let the optical line terminal (OLT) and optical network terminal (ONT) communicate and assess the optical power levels of the downstream/upstream signal at the same time. Also, a PON-aware power meter will avoid any false results that can be caused by the overlay of legacy and next-gen PON technologies on the same fibre by measuring each stream independently and applying the right thresholds.
Fig. 2: Two-stage architecture with G-PON and RF video services.
Automated field test management solution
A cloud-based field test management solution will allow managers to pre-define and assign jobs that will automatically sync with field test equipment, significantly reducing the time field technicians spend on administration tasks while minimizing risks of data entry errors. End-to-end solutions will include reporting capabilities, automated close-out packages and batch validation, as well as insightful analytics. Such a tool ensures 100% compliance of methods of procedures (MoPs), speeds up invoicing and deployments as well as help making better business decisions.
Test and monitoring solution for gigabit Ethernet speed and WiFi testing
A gigabit Ethernet speed tester provides real-life throughput up to full line rate gigabit Ethernet by using Speedtest by Ookla while removing the effect of their home hardware or installation setup. WiFi channel map capabilities will enable technicians to test the WiFi signal in all rooms of the house to ensure optimal signal distribution.
FTTH network phases
Fig. 3: Example of a filtered test cord for live network testing.
Different criteria need to be considered when shopping for test equipment, depending on the respective phase of the network cycle. Speed, consistency and efficiency are the most important testing parameters to keep in mind during all phases, but here is a simple breakdown:
Construction or deployment phase
When building a FTTH network, it’s important to follow the same processes regardless of topology and splitter configuration.
This portion of the network can be either an existing network or a new cable installation. This link is tested using the “standard” method to verify that splices are within specifications and losses are as expected. Typically including bi-directional OTDR measurements.
Here a fully connected network is tested from the drop terminal to the CO. The network may be spliced or connectorised through different points, but whatever the topology, you can use the same process. Working with experts in FTTH testing can be a considerable advantage at this stage.
A fibre inspection probe is used to test the ports being deployed in the final part of the built network. All the ports can be tested or only the ports that will be used for the next stage of testing. This is decided according to the pilot or trial.
The ports are then tested with an intelligent iOLM. The major benefit of using an iOLM is that you can create a test configuration and parameters suited to specific network designs. In this test configuration, you can hard code the pass/fail criteria of splices, connectors (both loss and reflectance), splitter enclosure losses, overall link loss and ORL.
Additionally, an OLTS can be used to assess the network’s overall link loss. This is a characteristically speedy process that validates each port for overall loss guaranteeing 100% network compliance from day one.
Consolidating these results using a reporting tool with bespoke templates for contractors to use will further enhance the test process, as the results format and testing criteria will be locked into a quick and easy report template for quick confirmation that the test results pass the criteria set for the network.
These simple steps offer the certainty that the link deployed between the CO/PoP/exchange has the correct connectivity, cleanliness and fibre oraganising and is within the expected loss budget (a margin typically applies).
Once the last step is complete, the OLT can be connected to the ODF and all the splitter ports at the drop terminal will go “live.”
Broadband/service activation or delivery to the subscriber
Once the network has been shown to be operational in the construction or deployment phase, the task of connecting the subscriber to the service should be straightforward. Before disturbing the subscriber on the day of the delivery, the engineer should verify the optical power at the drop terminal. This can be done with a conventional power meter, set to 1490 nm for GPON without RF video, or with a PON power meter that will discriminate power from multiple downstream layers such as 1550 nm RF video over GPON or any combination of GPON and next-gen PON services, such as XGS-PON and NG-PON2. This will confirm that the downstream powers are within budget. Once you have downstream power confirmation, the drop cabling can be installed.
You can then repeat the process above, but with the added benefit of testing upstream power with a power meter that has this capability. By connecting the power meter in series with the ONT, the ONT will start communicating with the OLT and both the burst upstream and downstream power can be verified in pass-through mode, keeping the service live. Results can be stored as a “birth certificate” as part of the installation.
With the ONT connected, you should have a service for the customer. However, to confirm the service is as expected (300 MB or 1 GB as an example), be sure to verify that this is the actual service being delivered. By taking the input to the ONT and connecting it into an independent speed tester (not limited by PC or WiFi speed/design) running a Speedtest by Ookla will provide a result that will be familiar to your customer.
It is recommended to generate a report on the subscriber’s system to avoid any potential complaints not related to the service installation and avert unnecessary truck rolls.
Troubleshooting and maintenance of any service disruptions
Troubleshooting and maintenance in any FTTH network will be a combination of many of the tests performed in previous phases. The approximate location of a fault at an individual residence, business or a group of these can be determined by the service disruptions or complaints reported. With this information, you can then identify what type of test is needed to locate the exact fault.
One of the most important tools for this phase is an OTDR or an iOLM with a filtered patch or port working with an out-of-band wavelength. OTDR with 1310/1550 nm used in construction could not be used on a live network as the OTDR cannot unmerge downstream signal power from the backscattering of its own emitted pulses (even risking burning OTDR detector). Also, the OTDR 1310/1550 signal could disrupt upstream live traffic on the PON network and potentially damage SFPs at the OLT. The only solution is to use a filtered live port that will significantly attenuate any incoming traffic and allow testing to be performed without impacting other subscribers.
Testing with a filter cord/port at either 1625 nm or 1650 nm will show and locate any breaks or high losses very clearly. Due to time constraints, many networks are built first and then tested, so by knowing what and how to test allow technicians to test at any stage of the built network.
Low power or slow speeds issues can be diagnosed as described above with a power meters or a test and monitoring solution, by cross-referencing results obtained during subscriber activation stage.
Investing in testing gear
Investing in FTTH dedicated testing equipment is key to overcoming challenges and potential incremental deployment costs. Operators need to determine the best return on investment for their network and be conscious of future needs.
Testing FTTH networks is a balancing act involving many factors and finely tuning these factors gives providers and contractors the assurance that their network is tested right the first time. Organising the following benefit statements and risk factors in order of priority can help finding the right balance for the project make the best budget decisions. Make sure you explore all your options so that you choose the solution that is best suited to your project and will present the most benefits while minimising risks.
Conclusion
While it may sound appealing to deploy your network quickly for faster time to revenue and relying on troubleshooting to fix issues later, the risk of expenses getting out of hand if too many issues arise is greater than having full visibility over your investment right from the start. Investing in reliable test equipment is key for successful FTTH deployments that will be future proof.
Contact Chris Nel, Lambda Test Equipment, chris@lambdatest.co.za
