TECHNICAL
time, but bad installations result in re- work, repeat truck rolls and delays in activation. Installers need to inspect every time they make a connection. Proper qualification during construction means doing testing not only at 1310/1550nm but also at 1625 for NG-PON2, storing of test results, and for contractors, easy submission of results (to get paid quicker). For service activation, power levels of all downstream and upstream services must be verified. With the use of new wavelengths for XGS-PON as well as for NG-PON2, there is a need for new PON power meters, like VIAVI OLP instruments, that enable wavelength-selective, through-mode power measurements. Support for ongoing operations requires troubleshooting tools that won’t disrupt those existing services, in order to be used in-service and be future proofed avoiding those XGS-PON and NG-PON2 wavelengths means using 1650nm. There is also a case to be made for centralised PON monitoring to reduce service outage time, Mean Time To Repair (MTTR) and guarantee high quality of service for high-speed access networks. Next-generation PONs will help service providers launch and sell in-demand, on-demand services to their customers. However, as we know, innovative technologies can bring new challenges – especially during the time of evolution from one standard to another. While NG- PON2 is a very promising approach, it does come with new considerations that are best mitigated with consistent, basic testing during construction, installation and deployment. After all, higher capacities mean more services are riding on their networks—which means more reward, but also more risk.
There are several failure risks that can affect the success of roll out plans, migration timelines, service quality and churn rates (see Figure 2). Here are some of the vulnerabilities exposed with all variants of PON services/standards: n Dirty connectors, bad splices and microbends that add loss, which means the total ODN loss no longer meets the standards; such conditions lead to intermittent or poor service (or no service)
While evolving networks and standards mean things are getting more complicated, test equipment should remain simple to use to ensure job and workflow efficiency.
n Splitter elements can be faulty
n Transposed fibres caused by human error when connecting a fibre to a wrong splitter port n Rogue ONTs that transmit outside of their allocated upstream time slot, which results in upstream clashes with other ONTs and service disruption n Alien devices, where a subscriber has accidentally installed other devices than an ONT (e.g., a media converter). These devices may send continuous upstream traffic that interferes with other ONTs in the PON and degrades or interrupts the service. Even greater vulnerabilities exist around in-house cabling. As with any fibre connection, making sure end faces are clean and free from any damage is key. Macrobends due to bad cable installation practices are a key issue to be aware of for XGS- and NG-PON2 deployments. Those services are using higher wavelength bands (>1550nm) that are more sensitive to bending loss. Installers, contractors and subscribers may simply not be aware of the issue that small bending radius in indoor cable installation will cause excessive loss and degrade service performance. Even when using new bend-insensitive G.657B fibres, bending loss may reach more than 1dB when cabling radius reaches values <7.5mm (e.g., around corners). Having an installer perform this check as part of an install is relatively easy to implement, but subscriber self-installs remove that assurance. In fact, self-install may not be the best approach for higher- speed, higher-revenue services like XGS- PON and NG-PON2. While evolving networks and standards mean things are getting more complicated, test equipment should remain simple to use to ensure job and workflow efficiency. Testing does take
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DECEMBER 2024 Volume 46 No.4
89
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