The Next Stage in Fiber Network Evolution —
Passive optical network (PON) technologies have a long history and reputation for efficiently adapting to new challenges. From BPON to 10G XG-PON and NG-PON2, the fluidity of PON technology has consistently proved itself to be unparalleled for record-breaking speeds, dual-rate bitrates, and multiple lambdas.
Now with the advent of 5G mobile networks, PON is once again being called upon to tackle a new challenge. As 5G brings greater connectivity speeds it also creates more demands on mobile transport networks. To address this challenge, the blueprint for PON technology and its capabilities is being redrawn to introduce a new hero: 25G PON. The technology enables operators to establish better synergies between fixed and mobile networks through fiber assets as a unified infrastructure for both.
25G PON is disrupting the status quo and leveraging the data center optical technologies to bring the most cost-efficient solution for PON beyond 10G.
A New Hero
There are 2 requirements for 25G PON to be successful. The first is cost-efficiency, which, in a large-scale access network deployment, is key. 25G PON operates in a mature eco-system and leverages the high volume of 25G optical technologies used to interconnect data centers. In addition, as a simple TDM technology, 25G has no requirement for costly, tunable lasers. (See Figure 1.)
The second requirement is the market readiness for the technology, namely in the form of clear use cases such as residential, business, and 5G anyhaul. The residential market presents a potential opportunity for aggregation of Gigabit services on high-density PON. This includes headroom (reserve) for speed tests. In the business sector, 25G PON will allow for full 10G services, or possibly higher, to be extended to the enterprise.
25G can also enhance the value of PON networks for mobile transport. While XGS-PON or 10G P2P can efficiently manage mid-haul and backhaul today, 25 PON will be required to address higher density (more cells per PON) and higher throughput per cell from increased RF bandwidth and MIMO antenna layers.
Additionally, 25G PON is up to date with the mobile network evolution, with 25G physical interfaces due to be used in radio units. Also, 25G will enable telcos following ITU steam standards to respond to operators using IEEE based 25G EPON technology, ensuring competitiveness in the market.
Compared to alternative routes for PON evolution, 25G PON best hits the cost, demand, and time to market targets. For example, 50G PON is currently a premature ecosystem that is not expected to come into its own before 2025. Additionally, the types of services and deployments that will drive 50G bitrates have yet to manifest themselves.
Other options include wavelength bonding, which could be done with tunable or fixed optics. 2x10G bonding with fixed optics uses 1 GPON wavelength and 1 XGS-PON wavelength. The disadvantages of this approach are higher cost and complexity (2x10G optics is more expensive than 1x25G optics), and lack of ability co-exist with current GPON deployments — resulting in no market traction.
Equally, the option to leverage 2xTWDM-PON turntable wavelengths, would require 2 expensive lasers in the ONU to bond the 2 wavelengths, and wouldn’t be cost-effective.
The Natural Successor
Although not yet at the point of commercial deployment, 25G PON has all the makings to become the best approach to evolve fiber networks in line with residential, business, and mobile transport, requirements.
In addition to being a cost-effective, market-ready solution, 25G PON can co-exist with GPON and XGS-PON technologies while offering higher bitrates: 25Gb/s downstream and 10Gb/s or 25Gb/s upstream.
Nokia has been at the forefront of 25G PON’s development, releasing the industry’s first proof of concept, and showing that 25G PON can be used to carry 5G mobile mid-haul traffic. With the ability to significantly enhance speeds and converge services over a single fiber network, the technology is an exciting development that has enormous potential to impact the future of broadband.