Why 25G PON is right for the 10G era


Fiber broadband technology evolution is not really about technology: it is about business opportunity. Successive generations of PON technology have increased performance levels, providing the opportunity for PON to deliver unbeatable residential services and go beyond residential broadband into higher ARPU 10G services for businesses, factories, mobile backhaul, smart cities, and more.

In the UK, for example, there are more than 50 altnets building fiber networks. Competition is driving down residential broadband prices to as little as £25 per month in central London. Interestingly, Gigabit business services with a reasonable level of service agreement creates 10x more revenues, at around £270 per month. So, by adding only three business customers, a service provider can roughly double their income on a PON. Take that service level up to 10Gb/s, and ARPU goes beyond £700 per month.

10G opportunities are here today and make for an extremely compelling ROI for fiber network operators. So, what is the best way to deliver 10G?

Until recently, that speed could only be delivered by point-to-point (P2P) fiber. P2P is more costly than PON: it requires more equipment, more real estate, more fiber cabling, and consumes more energy. P2P is also an overlay network, so operators end up running both PON and P2P, which increases costs. Hence, there is a growing appetite for converging business services onto PON networks.

How can this be done successfully? XGS-PON (10G symmetrical PON) networks are becoming more widely deployed, already delivering multi-gigabit connectivity to businesses worldwide. But XGS-PON cannot reach true 10Gb/s because its capacity is limited to 8.5Gb/s due to standard specified overhead. The good news is that XGS-PON can easily run faster with 25G PON, delivering true 10G speeds and beyond from the same hardware that is being deployed today for XGS-PON. And this is already happening. There are now 1 million PON lines worldwide capable of 25G PON, enabling operators to address 10G opportunities very efficiently, and that number is growing fast.

More good news is that 25G PON can be complemented with 50G PON in the future, because the two technologies can co-exist. This will enable the delivery of even higher speeds to more customers, but that is not quite the case yet.

A fully mature 50G symmetrical solution ready for volume deployments will take many more years. Unlike 25G PON which is a straightforward evolution from the current solutions, 50G PON is a technology leap involving a new generation of components that need to mature and reach high volumes to become cost-effective. In addition, the migration to 50G PON requires the introduction of new hardware, which takes time and money. The first demonstrations of 50G PON are asymmetrical with 50Gb/s in downstream and 25Gb/s in upstream. Business services are defined as symmetric, so asymmetrical 50G PON brings no advantage over 25G PON. And finally, since both symmetrical and asymmetrical 50G PON variants share the same wavelengths, operators will need to consider swapping all 50G ONTs when they introduce the symmetrical variant. The industry has seen this kind of issue before with 10G PON, which was one of the reasons operators skipped asymmetrical XG-PON and preferred to wait for symmetrical XGS-PON.

So, is it worth considering 50G PON? Absolutely! But it doesn’t mean you have to make hard decisions between 25G PON and 50G PON, because one doesn’t exclude the other. Every operator should evaluate if they can afford to wait for fully mature and deployable symmetric 50G PON, or address the real opportunities today with 25G PON, while having an open path to 50G PON in the future.

25G PON is the most optimized solution for 10G era, and here’s why:

It is available, mature and being deployed today. No need to wait and lose opportunities to competitors.
It is easy to introduce. The OLTs and line cards in use today for GPON and XGS-PON can also support 25G PON. It’s just a case of plugging in the 25G transceiver.
There’s huge capacity for 10G business services and beyond, with enough bandwidth left over for residential broadband and mobile backhaul.
It’s the most power efficient technology for the 10G era. 25G PON delivers a 10-fold capacity boost over GPON for only a 2.5-fold power increase, consuming 0.25 watts per gigabit. 25G PON’s limited power consumption allows an ONU to be integrated in an SFP form factor (aka ONU on stick) for business and mobile transport applications, while this is not sure for 50G PON.
Backward compatibility with GPON and XGS-PON and forward compatibility with 50G PON make for assured migration paths.
It’s cost-efficient as 25G optics and electronics are mature, with component prices coming down faster than 10G components. Since 25G PON is available on existing hardware, there is very little additional investment to be made.

The industry’s experience with GPON also tells us about commercial sweet spots. Operators successfully deploy 1 Gigabit services on 2.5G GPON networks. This 1:2.5 ratio holds true for 10G business services on 25G PON.

As ever, the decision on which technology an operator will adopt comes down to the business case: when does an operator need it, and at what cost. With 25G PON offering an immediate path into highly lucrative 10G business services, the return on an investment in 25G PON looks highly appealing. All the benefits now, while leaving an open path to symmetrical 50G PON in the future.

Learn more about our 25G PON solution.

This article was written by Ana Pesovic
Ana heads the Fixed Networks Fiber marketing activities in Nokia. She built up extensive international telecom experience, with positions in sales, pre-sales and R&D in Germany, Spain, Portugal, Belgium and India. Ana has a Masters Degree in Informatics and Computer Science from the University of Belgrade. As member of the Board of Directors of the FTTH Council Europe, she’s a strong advocate of Fiber.

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