Why Combo PON makes next-generation PON better

New PON technology efficiently merges GPON and XGS-PON resulting in huge cost and capability benefits.
Kurt Raaflaub

Since Adtran pioneered XGS-PON, there has been an ongoing industry debate regarding when and where a fiber-to-the-home (FTTH) network operator should employ fiber broadband services using GPON versus XGS-PON standards. The availability of Combo PON capabilities built into second-generation XGS-PON solutions concludes the debate because an operator can now leverage both FTTH standards without sacrificing cost or capability.

As first-generation XGS-PON solution costs have fallen over the last couple of years, XGS-PON electronics have leveled off at about 20 to 30% more than 15-year-old GPON electronics. When comparing the entire FTTH network buildout, that comes out to only 2 to 3% more capital per home to support the increased capability of symmetrical multigigabit PON services. Due to this, almost all greenfield networks today are being built using XGS-PON. Where service providers may balk at the need to deviate from tried-and-true GPON technology, there are those smaller brownfield GPON networks that demand neither the added network capacity nor the multigigabit service differentiation offered by XGS-PON.

First-generation XGS-PON provided the ability to simultaneously overlay a much higher-capacity FTTH technology on the original GPON-powered fiber network. If free space is available within the FTTH platform, CO rack, or cabinet, a new XGS-PON FTTH module and the required external coexistence module could be installed with little consequence, save for the optical budget impact of the external coexistence module. This XGS-PON overlay would enable the FTTH operator to offer differentiated multigigabit services and considerably increase the network’s capacity to deliver 100Mbit/s and Gigabit services.

Figure 1: Combined XGS-PON and GPON technologies on a common ODN and separate OLT systems.
Combo PON allows both GPON and XGS-PON services to be deployed on the same optical distribution network (ODN), but unlike first-generation XGS-PON technology, it does so without requiring external coexistence element (CEx) modules to combine the services of each technology onto the same fiber. This is possible by having both GPON MAC and XGS-PON MAC supported from a common optical line termination (OLT) port. At the same time, the optics combine the two technologies on one optical fiber.
Figure 2: Combining XGS-PON and GPON technologies within a common OLT module (line card).

Combo PON provides the ability to merge highly mature GPON networks with next-generation 10G XGS-PON technology while combining their respective values. An operator may deploy GPON to deliver highly competitive 100Mbit/s services leveraging ultra-low-cost GPON-based home gateways while using XGS-PON to offer differentiated home and enterprise services at a price premium.

Second-generation XGS-PON, inclusive of Combo PON technology, provides improved economics for operators building new FTTH networks or modernizing existing GPON fiber networks to support the economic and social development of the communities they serve. Quantifying the economic benefits, when upgrading to XGS-PON on an existing 20,000-subscriber GPON network, Combo PON affords service providers up to 75% reduction in space, 66% power reduction, and 50% reduction in capex when compared to operating two discrete GPON and XGS-PON optical OLT systems.

Figure 3: Combined XGS-PON and GPON technologies on a common ODN and OLT system.

Without combo PON, this higher density XGS-PON overlay scenario would require an additional two chassis worth of first generation XGS-PON OLTs in addition to the necessary external coexistence elements using second generation XGS-PON OLTs, leveraging Combo PON, this added gear is eliminated affording the network operator to make an in-skin replacement within the existing single chassis. Three chassis of OLTs reduces to one with the CEx gear requirement also eliminated, and no new network uplink ports are required. This equates to a 75 percent reduction in space. Fewer OLTs operating translate to less power consumption and less heat dissipation (66 percent less), and up to 50 percent less capital expense. Further, on the operational side, it is all quite transparent: no ODN impact, same splitters, same optical budget; no customer impact; no home visits, Combo PON auto-inherited provisioning from existing GPON service. On the revenue side of the business case, elimination of an external coexistence module increases the optical budget affording the network additional fiber reach, extending the service area by an extra 20 percent. More customers served means more services revenue generated.

Not only does Combo PON provide all of the first-generation XGS-PON capacity and operational benefits, but it also affords the opportunity to leverage the full value of mass market GPON technology while further simplifying fiber network modernization processes, thus making Combo PON the next next-generation FTTH solution.

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