What is Combo PON?
OK. You aren’t quite sure about the choice between Gigabit Passive Optical Network (GPON) and Ten Gigabit Symmetric Passive Optical Network (XGS-PON) to power your optical distribution network (ODN).
Let’s face it. The difference in the cost for a GPON based Optical Networking Unit (ONU) and an XGS-PON based ONU can be large enough, especially that when scaled to 100,000 subscribers or more, to tilt you to favor deploying your access network with GPON.
Many operators, though, look beyond the 20-30% increased cost of XGS-PON electronics over GPON and compare the overall cost to connect a FTTH subscriber. With the ONU making up a small portion of the overall connection cost, the cost adder for using XGS-PON over GPON ranges most of the time between 2 and 3%. So, is the extra cost delta justifiable?
Figure 1 GPON and XGS-PON comparison
Supporting More Subscribers, Better Services
If you were to switch to an XGS-PON network, you benefit from the network capacity required to expand your existing network footprint and increased service take rate. The network capacity to offer lucrative multi-gigabit services directed at premium residential and enterprise customers and do this all cost effectively using a single common ODN.
When an operator chooses XGS-PON to power their network they afford themselves the expanded network capacity to support the upcoming proliferation of streaming 4k cameras, uncompressed gaming and streaming services and mitigate the ensuing spike of failed gigabit speed tests that would follow. With a GPON network, an average peak rate of 4Mbps upstream and 25Mbps downstream will greatly elevate the number of failed gigabit speed tests and the quantity of costly customer cares calls. That level of bandwidth growth equates to a couple 4k cameras and one 4k video stream usage per home at peak time. But when will that happen?
A case for Combo PON
So, how do you best position yourself today to benefit from the economies of GPON and migrate to XGS-PON with minimal investment and fastest time to market to power your ODN? Let’s consider all the alternatives.
How about GPON now and XGS-PON later?
Since the two technologies operate on different wavelengths – GPON uses 1310 nm in the upstream and 1490 nm in the downstream, while XGS-PON uses 1270 nm un the upstream and 1577 nm in the downstream – it is possible for both GPON and XGS-PON to co-exist on a single ODN. Coexistence is extremely handy, since it allows you to serve different customers and cater to different needs on the same ODN.
Figure 2 Converged GPON and XGS-PON on a single ODN using a Co-Existence Module
Deploying GPON now and XGS-PON later is fairly simple. All you need is to multiplex the new XGS-PON ODN with the existing GPON ODN using a co-existence module. This is where an operator benefits from the economies of scale and breadth of choice offered by GPON and delays the cost adder of XGS-PON for later or never if market drivers for increased capacity do not come to fruition.
This is also where operators risk losing subscribers and impacting customer care as Quality of Experience (QoE) levels deteriorate, while the network team looks to fund, deploy and operationalize XGS-PON, and , of course, there is then the economic impact of truck rolls to upgrade customers premises gear to support XGS-PON.
How about both GPON now and XGS-PON now?
The second option to consider is deploying both GPON and XGS-PON today with or without a co-existence module, using a GPON OLT and an XGS-PON OLT. This solution gives you a clear separation between subscribers that you wish to keep on GPON network versus those you wish to keep on an XGS-PON network. Because of the separation, each PON port can be used to serve up to 128 subscribers. The flip side, of course, is the extra investment to fund and maintain the architecture, and the difficulty associated with moving GPON customers to the XGS-PON network in the future, if need be. Could there be a better alternative?
How about both GPON and XGS-PON now, but better?
Figure 3 Combo PON
Combo OLT uses Combo PON transceivers that integrate the co-existence module with GPON and XGS-PON transceivers into a single pluggable entity. The GPON portion of the transceiver plugs in to a GPON Media Access Control (MAC) chip, while the XGS-PON portion of the transceiver plugs in to the XGS-PON MAC chip. Since, we are limited by the power levels on these transceivers, the end split ratio of the Combo transceiver is still limited to 128 splits. The advantage of deploying with Combo PON OLT is that you can serve GPON customers today, and later add XGS-PON customers without having to add any new equipment Since most of the cost differential between GPON and XGS-PON deployment is on the ONU side, Combo PON OLT makes for a perfect recipe for low cost upfront investment in GPON and least disruptive and most economical migration to XGS-PON.