Size a GPON, XG-PON, XGS-PON or NG-PON2 network from a subscriber target to ONTs, PON ports, line cards and OLT shelves, with the bandwidth limit, the binding constraint and fair share at peak.
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Overview
PON sizing often collapses to a single figure, subscribers per PON port, and that is where mistakes hide. The real path is a chain: one PON port feeds a 1:N splitter, each splitter output feeds one ONT, each ONT has a number of Ethernet ports, and each port serves an access point with its own subscribers. If the chain is wrong, a splitter can be oversold against the bandwidth available, or a rollout across several buildings can strand half its splitter outputs.
The planner works through that chain explicitly. Each step is a plain number, subscribers per ONT and per PON port are derived as you type, and the bandwidth model for the selected standard (ITU-T G.984 GPON, G.987 XG-PON, G.9807 XGS-PON or G.989 NG-PON2) is run against peak concurrency, over-subscription and protocol efficiency. The result is the number of ONTs, PON ports, line cards and OLT shelves needed, with the limiting constraint named: downstream or upstream bandwidth, the ONT limit per port, or the splitter ratio.
Distribution points are part of the model. Subscribers are spread evenly across them and each one is sized on its own, because a partly filled splitter cannot be shared between locations, so sparse sites are not under-counted. Comparison tables run every splitter ratio and every PON standard against the same design, a growth percentage shows the extra equipment a larger subscriber base would need, and the standard and splitter ratio are shared with the PON Optical Budget Calculator.
The design is built from PON port to splitter, ONT, Ethernet ports, access points and subscribers, rather than from a single subscribers per port figure. A diagram of the chain shows the running count at each step, so every multiplication can be checked.
Subscribers are spread evenly across distribution points and each point is sized on its own, then the totals are added up for the OLT. When the splitters at each point would be less than half full, the planner suggests a smaller splitter to reduce stranded outputs.
For the selected standard, the ITU-T nominal line rate is reduced by protocol efficiency and compared with the per-ONT load at peak, based on bandwidth per subscriber, concurrency and over-subscription. Efficiency, concurrency and over-subscription have no standard value, so they are labelled design assumptions, and a blank input is named rather than filled in. You can limit on downstream, upstream or whichever is worse, and per-PON demand at full splitter fill is flagged when it exceeds the usable rate.
Downstream bandwidth, upstream bandwidth, the ONT limit per PON port and the splitter ratio are compared side by side, and the lowest is named as the binding constraint. When bandwidth could support more ONTs than the physical limits allow, the spare headroom is shown.
The usable line rate is divided among the subscribers active at peak when the PON is filled to its effective maximum, giving the downstream and upstream share for each subscriber and each ONT. This is a useful figure to set against an advertised headline speed.
Tables run every splitter ratio and every PON standard against the current design, showing the ONTs per port, fair share and equipment counts for each. They show whether a faster standard saves PON ports or only adds speed per subscriber.
A growth percentage runs the same model for a larger subscriber base and shows the extra ONTs, PON ports, cards and shelves. The PON standard and splitter ratio are shared with the PON Optical Budget Calculator, and the results copy to the clipboard as a text summary.
Inputs and outputs
Inputs 11
Outputs 10
Use cases
It builds the design from the downstream chain. The splitter ratio, Ethernet ports per ONT and subscribers per access point give subscribers per ONT and per PON port. The bandwidth model then sets the maximum ONTs per PON port, and the subscriber count is worked up to ONTs, PON ports, line cards and OLT shelves.
Each distribution point needs its own splitter, and a partly filled splitter cannot serve subscribers at another location. The planner spreads subscribers evenly across the points, sizes each one on its own and adds up the totals. With few subscribers per point, this can need several times more PON ports than a single aggregate calculation would suggest.
The number of ONTs one PON port can carry is limited by downstream bandwidth, upstream bandwidth, the ONT limit per port and the splitter ratio. The binding constraint is the lowest of these, and the planner names it so you know what to change to serve more subscribers per port.
GPON (ITU-T G.984), XG-PON (G.987), XGS-PON (G.9807) and NG-PON2 (G.989). The selected standard sets the downstream and upstream line rates used by the bandwidth model, and a comparison table runs all four against the current design.
Fair share is the usable line rate, after protocol efficiency, divided by the number of subscribers active at peak when the PON is filled to its effective maximum. It is reported for downstream and upstream, per subscriber and per ONT.
No. The ONT limit per port, PON ports per card and card slots per shelf are plain numbers you set to match the equipment you are using, so the planner can be used to review any vendor's proposal.
No. The calculations run in your browser, and your design is kept in your browser's local storage between visits. The PON standard and splitter ratio are shared with the PON Optical Budget Calculator in the same browser.
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