The role of next generation PON technologies in FTTX

Nov 14, 2023

Advanced test equipment is required for new forms of passive optical networks, says Richard Martin of Electro Rent.

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The prevalence of fibre-oriented communication infrastructure continues to grow across the continent of Europe. A recent report compiled by market consultancy firm iDate predicted that the number of fibre-to-the-home (FTTH) and fibre-to-the-building subscribers within the EU/UK will grow from 49 million today to 148 million in 2026.

The number of residences where fibre-to-the-kerb services can be accessed will be very close to doubling during that period, with an increase from 105 million to 202 million expected. The UK, Germany and Italy are among the countries in which much of the envisioned FTTX (all types of fibre infrastructure) investment is going to take place.

Passive optical network (PON) technology has been pivotal in allowing broadband operators to undertake large-scale FTTX projects, providing a straightforward and cost-effective means via which implementation work can be done. As this medium continues to evolve, with the advent of next generation derivatives, the data rates and split ratios that PON-based FTTX will be able to support are going to increase dramatically. However, it also exacerbates the sizeable test challenges already associated with PON.

The underlying dynamics driving FTTX rollout (such as more connected devices per household, alongside the growing popularity of online gaming, 4K/8K video streaming and cloud services) were already evident. Other factors, however, must be added into the mix. For example, the changes to working culture in the aftermath of the global Covid-19 pandemic are certain to have a significant long-term influence too. A larger proportion of the population is now working from home and it is likely that many will be at least part home-based in the future. Residential broadband demands are therefore going to remain high and, in response to this, the rate at which FTTX deployment activity is undertaken is almost certain to accelerate considerably.

Gigabit PON (GPON) was introduced in 2003. This had the inherent point-to-multipoint shared fibre benefits of PON and the ability for more subscribers to be served by a given infrastructure investment, while markedly raising the data rates that could be supported. It had downstream speeds of up to 2.5Gbps and 1.25Gbps upstream speeds.

Over the next few years, GPON was followed by other asymmetrical standards. Ever rising bandwidth demands meant that greater speeds were needed. As user behaviour changed, the differentiation between upload and download requirements became less apparent. This would drive the need for symmetrical standards.

The introduction of XGS-PON (which can support 10Gbps symmetrical data transfer rates) enabled single-channel 10Gbps data transfer in both directions via the use of wave division multiplexing. After this came NG-PON2, which means that symmetric operation may now be delivered across four and eight downstream and upstream channels respectively. This translates into a total capacity of up to 80Gbps available on a single fibre. Key to this technology is the use of time and wave division multiplexing and the incorporation of tuneable lasers into the system.

With GPON, the 1490nm and 1310nm wavelengths are used for downstream and upstream respectively. For NG-PON2, 1600nm is used for downstream and 1530nm for upstream traffic, whereas XGS-PON relies upon 1577nm for downstream and 1270nm for upstream. The ability of these two newer standards to coexist with GPON is important. It means operators can address different customers’ service level requirements while using much of the same infrastructure to protect earlier investments. It also means that when an upgrade is finally needed, it is straightforward for operators to migrate a GPON network to XGS-PON or NG-PON2, with most of the deployed hardware (in particular the fibre laid) staying unchanged and only certain optoelectronic devices needing to be replaced.

The fact that XGS-PON and NG-PON2 both rely on downstream wavelengths that are higher than conventional GPON does have certain drawbacks. Most notably, it exposes them to greater power losses. Use of multiple wavelengths also adds substantially to the complexity of test procedures. There are other potential issues to contend with, such as heightened susceptibility of the output to bends in the fibre caused by poor installation.

There is equipment suitable for both legacy and next generation PON infrastructure. An example is Exfo's P-174631 FTTH contractors’ kit. It consists of the pocket-sized EX1 GPON tester, an OX1 fault detector and a FIP-4858 fibre inspection probe.

The SmartOTDR handheld fibre tester from Viavi analyses networks that are using the latest PON standards. It enables detailed troubleshooting work to be undertaken through its optical time domain reflectometry and visual fault location functions, with the ability to deal with up to 256,000 data points. The company's Smart Link Mapper software is claimed to make test data easier for the operative to interpret – so testing procedures are completed quicker and the risk of errors occurring is kept to a minimum. The unit has power-metering capabilities built in, with 1310nm, 1490nm, 1550nm, 1625nm and 1650nm calibrated wavelengths.

The arrival of XGS-PON and NG-PON2 has taken fibre networking to another level, enabling 10Gbps symmetric services to be delivered to homes. It does, nevertheless, call for more sophisticated test procedures, along with access to instrumentation incorporating all the appropriate functionality. The fast-moving nature of the FTTX (fibre to the destination of the fibre optic line) sector means the infrastructure needs to be rolled out within short timeframes.

Additionally, the regular emergence of new standards means that the direct purchasing of new equipment might not be a financially valid strategy. It may be prudent for alternative sourcing methods to be considered instead.

Implementing a more effective test strategy, which encompasses the various different equipment sourcing methods, should ensure that available inventory is better matched to current requirements (and subsequently adapted as these change). Rental allows equipment that is no longer in use to be quickly upgraded to other items for which a pressing need has been identified. Equally, the number of units can be scaled up or down to address any fluctuations in demand that are experienced over time.