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In prior blogs, we’ve explained what Combo PON is and discussed why deploying XGS-PON using Combo PON technology is better for a fiber network operator. Most fiber network operators now recognize its most basic benefit as a technology that empowers operators to enable both Gigabit Passive Optical Network (GPON) and Ten-Gigabit Symmetric Passive Optical Network (XGS-PON) on the same Optical Distribution Network (ODN) over a single, common OLT port. In this blog, I will focus on the power of PON coexistence using Combo PON and how it enables operators to extend the lifespan of their fiber infrastructure, specifically looking at when GPON can be expected to have fulfilled its useful life.

First, we have attempted to construct a predictive model to help determine when a GPON port will become a bottleneck for Gigabit broadband consumption. Federal Communications Commission (FCC) has defined three user types in its Household Broadband Guide. Similar to these guidelines, we have constructed the following model with four user types – Super Users, Heavy Users, Regular Users, and Low Users. The average measured Busy Hour Offered Load (BHOL) used in this model is 4.75Mbps with an expected CAGR of 30-50%. 4.75Mbps BHOL is based on measured industry wide data usage estimates.

Using a conservative growth rate in BHOL of 30%, we can predict the useable lifetime of a GPON port to the point that it becomes impossible to reliably deliver 1Gbps speed to a subscriber thus risking expensive contact center inquiries. Reminder that a GPON port supports an aggregate 2.5Gbps downstream and 1.25Gbps upstream. The charts below show that at a 1x32 split and a 1x64 split, GPON will have less than 1Gbps headroom by 2028 and 2026 respectively, making it impossible to deliver reliably 1Gbps in busy hour – which is when it is most needed! With such limited lifespan, greenfield deployments built using GPON will struggle to deliver normal payback of 8-10 years before needing to be upgraded to XGS-PON.

GPON Capacity

So, the big question – is how do you extend the lifespan of GPON? The answer – Combo PON! The solution lies in the power of coexistence and the underlying technology that builds coexistence into the transceiver.

Combo PON

Combo PON enables operators to deploy GPON and XGS-PON simultaneously off a single active port. The resulting architecture allows for interesting scenarios in segregating the heavy, moderate, and light users by appropriate PON technology. For instance, if we put all heavy and top half of the moderate users on XGS-PON and leave the remaining on GPON we notice that the lifespan of GPON technology in such a deployment increases by 2-3 years.



Low Usage Subs (GPON)High Usgae (XGS-PON)

Put in perspective, GPON technology, if deployed natively will become a bottleneck for Gigabit services in 5 years on a 1x64 split, but the same will survive 2-3 years longer if deployed over Combo PON technology through suitable allocation of PON resources based on broadband needs. This equates to an 40% increase in the lifespan of GPON.



Low Usage Subs (GPON)High Usgae (XGS-PON)

One might make the case that an integrated coexistence element isn’t necessary to see benefits of lifespan extensions. While true, the advantage of using a single active device or module that accepts a Combo PON transceiver is many folds as shown below. These benefits are relative to a disaggregated GPON and XGS-PON solution combined with an external coexistence module.

  • Price point of GPON – Capacity of XGSPON
    • Operators can begin deployment with GPON but have built-in capacity to migrate to XGS-PON anytime with little effort
  • 20% greater service coverage
    • An external coexistence element takes additional dBs hits that limits the distance at which subscribers can be supported
  • 66% less energy
    • A single-device solution uses half the power of a two-device solution
  • 75% less equipment space
    • A single device solution uses about 75% less space than two device solutions with an external coexistence module

In summary, coexistence with Combo PON provides tremendous flexibility in deployment scenarios that enables operators to start with a combination of GPON and XGS-PON and extend the life of their underlying infrastructure by suitably allocating resources to users based on broadband usage, thereby reducing the associated depreciation expenses and upgrade costs. Combined with the power, space, cost and service reach benefits afforded by the built-in multiplexing functionality in the PON transceiver, Combo PON makes for a fantastic choice for many small city and regional service providers looking to make the most of their fiber network investments.