Since Adtran pioneered XGS-PON, there has been an ongoing industry debate regarding when and where a 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, as an operator can now leverage both FTTH standards without sacrificing in terms of 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 percent more that 15-year-old GPON electronics. When comparing the entire FTTH network build-out that comes out to only two-to-three percent more capital per home to support the increased capability of symmetrical multi-gigabit 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 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, on the original GPON-powered fiber network, a much higher-capacity FTTH technology. 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 external coexistence module. More on that later. This XGS-PON overlay would enable the FTTH operator to offer differentiated multigigabit services and considerably increase the network’s capacity to deliver 100Mbps 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 on to 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 cost competitive 100Mbps 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 percent reduction in space, 66 percent power reduction, and 50 percent 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 required 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. Less 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, it 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.