NG-PON2: Not Your Father’s PON

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4 Wavelengths Help You Stay Ahead of the Curve:

Next Generation Passive Optical Networks (NG-PON2) is the ITU-T network standard for the latest generation of PON, a technology that transmits data through fiber optic cables, offering very high-capacity connections to multiple subscribers. More than just significantly enhanced speed, NG-PON2 offers extensive improvements over previous generations of PON that make it an ideal technology for opening new advanced services to MDUs, delivering mission-critical business applications, and readying the network for 5G mobile technologies.

Its most valuable application, however, may be as a catalyst to access network transformation. NG-PON2 technology enables the ability to converge multiple services networks onto a single optical distribution network (ODN), resulting in significant TCO reduction, as well as introduces new efficient architectures that are highly tuned to meet emerging subscriber demands.

From a consumer perspective, faster technology can’t come soon enough. Market forecasts predict that by 2020, more than 26 billion networked devices and connections globally will generate nearly 3 times the traffic generated in 2015.1

As bandwidth demands continue to grow, the ability to deliver 10 Gbps to individual businesses and households will be paramount for service providers to deliver the subscriber experience and services required to compete — and win.

It’s Not the Same as the Old PON
NG-PON2 was developed as a successor to GPON, which has been lighting up the world’s optical access networks with 2.5 Gbps downstream and 1.25 Gbps upstream for the past decade. GPON transmits data using a single wavelength on each fiber. Utilizing TWDM technology, NG-PON2 supports a minimum of 4 wavelength groups, making it the industry’s first multi-wavelength access standard. Each wavelength within a single fiber can deliver 10 Gbps symmetrical speed. When 4 wavelengths are combined, throughput can reach 40 Gbps and, in the future, it will be possible to combine 8 wavelengths to deliver 80 Gbps.

NG-PON2 was intentionally designed to use different wavelengths from GPON, allowing the 2 technologies to co-exist on the same fiber using already-deployed cables and splitters.

When migrating from GPON to NG-PON2, there are 2 primary investments that need to be made (See Figure 1.):
1. New ONUs supporting tunable lasers to support the compliant wavelength plans.
2. New OLT line cards to support compliant wavelength plans (as with the ONUs). In some cases, new OLT systems may also be required to ensure non-blocking support of NG-PON2 and to enable the desired density in the central office.

Figure 1. Multi-wavelength NG-PON2 OLT connected to ONUs with tunable lasers and receivers.

Potential Applications of NG-PON2
With the ability to deliver 10 Gbps and beyond to an individual subscriber, new business opportunities are possible, including:

Multi-Dwelling Units (MDUs)
Many existing structures lack in-building fiber optic cabling. When it is not possible to run fiber throughout the building, existing Last Mile technology, like G.fast over copper, is used to deliver broadband service to each individual unit. With NG-PON2, however, up to 40 Gbps can be brought to the MDU on a single fiber, making the delivery of gigabit services for each unit possible.

Mission-Critical Business Services
Forward error correction (FEC) is required to guarantee that services are not interrupted by attenuation caused by physical layer errors. Enabling FEC, however, limits the maximum bit rate that can be delivered over a single wavelength to 8.7 Gbps (in each direction). Thus, to deliver a true 10G service and meet Service Level Agreements (SLA), two NGPON-2 wavelengths must be used. This can be done using channel bonding.

5G Mobile Backhaul
As the industry continues its rapid movement toward 5G cellular technology, wireless data rates may reach as high as 10 Gbps. To backhaul traffic from the tower, connections exceeding 10 Gbps are going to be required. With NG-PON2, as the demand for bandwidth to a cell tower increases, it’s simply a matter of utilizing another wavelength over the existing fiber-to-the-tower.

In addition to increased capacity, NG-PON2 has 2 advantages over other PON technologies.
1. On-demand capacity management enables new service delivery opportunities and load balancing improvements.
2. Multiple wavelengths can be used to manage PON capacity. As utilization grows, PON capacity can be easily redistributed, with new channels turned on and ONUs switched over to different wavelengths, without impacting the delivery of existing services.

These changes can be done instantly, shifting and allocating capacity on demand, enabling new time-of-day services, and maintaining load balancing. Physical resources within the access network will be able to meet the dynamic needs of subscribers, without human intervention. (See Figure 2.)

Figure 2. On-demand capacity management allows wavelengths to be redistributed without impacting existing services.

Network Resiliency
With on-demand capacity management, ONUs can be switched to different channels, allowing for routine maintenance operations or network upgrades without service disruptions. In addition, fiber in the feeder plant can be isolated, providing similar equipment protection to what is available with Type B protection on GPON.

Two OLT systems can connect to a shared set of ONUs. The ONUs with the tunable lasers will range to a primary OLT. The ONUs will also be able to migrate to a secondary OLT. This represents a move away from simple equipment protection, to network resiliency, resulting in high network availability. (See Figure 3.)

Figure 3. Move from simple equipment protection, to network resiliency, by enabling 2 OLT systems to manage a shared set of ONUs.

The availability of multiple wavelengths enables a convergence of multiple services (residential, business, and wireless aggregation) on a single ODN. The ability to isolate each service on a dedicated wavelength provides important security benefits, while recognizing that each service is also likely to have different capacity requirements, operational constraints, maintenance schedules, and SLAs.

For example, one wavelength can be assigned to a business customer that requires a 10 Gbps connection for mobile backhaul. Using the same infrastructure, another wavelength can be used for residential Triple Play services. Residential subscribers can also be connected to an existing GPON line card, installed in the new OLT or left in the existing OLT, again using the same ODN. Referring back to Figure 1, you can see how service isolation can be achieved.

In addition, channel bonding enables increased capacity for an individual service. It does not increase the overall capacity of the fiber, but it allows for the grouping of 2 wavelengths on a single fiber. When 2 wavelengths are combined using channel bonding, a 20 Gbps service or beyond can be offered to a subscriber.

Channel bonding is the only way to offer a guaranteed 10 Gbps service to an individual subscriber when FEC
is utilized. Essential to the delivery of mission-critical business services, FEC is used to address attenuation caused by errors on the fiber. With as little as 5db of attenuation, data rates can drop by as much as 2 Gbps. More severe attenuation can cause more significant disruptions. FEC allows for uninterrupted data transport but, owing to the “overhead” of FEC, only NG-PON2 can deliver a guaranteed 10 Gbps service over PON with FEC enabled.

Transforming for the Next Generation
NG-PON2 is gaining momentum around the world. To date, NG-PON2 has been deployed in a live network by Northpower Fibre (New Zealand) using the Calix AXOS E7-2 with NG-PON2, and is in significant testing with Verizon who indicates they will deploy NG-PON2 in 2017.

NG-PON2 technology is key to the transformation of the access network. With the use of NG-PON2 technology, and the ability to converge the services networks onto a single ODN, there is a significant TCO reduction. Add to NG-PON2 new access network architectures like Central Office Re-defined as the Datacenter (CORD), Software Defined Networking (SDN), and more specifically for the access network Software Defined Access (SDA) with Network Functions Virtualization (NFV), the service provider will have transformed their access network to not only reduce their TCO but to also meet the needs of the ever more demanding subscriber.

Endnote:
1. Cisco Visual Networking Index (VNI) Forecast and Methodology, 2015-2020. June 2016. http://www.cisco.com/c/en/us/solutions/collateral/service-provider/visual-networking-index-vni/complete-white-paper-c11-481360.html

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About Author

Teresa McGaughey is Senior Director, Product Marketing, AXOS. She has more than 20 years of experience in access networks and access network technologies. For more information, please email teresa.mcgaughey@calix.com, and follow Teresa on Twitter @t_mcgoo, and on LinkedIn at https://www.linkedin.com/in/teresamcgaughey/. Also visit https://www.calix.com, and follow Calix on Twitter at https://twitter.com/TheCalixNetwork.

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