Build a fibre link loss budget from the installed plant: fibre segments, connectors, splices and an optional PLC splitter, checked against your design margin with link return loss and multimode reach.
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Walkthrough
End-to-end optical path with the loss at each stage.
Overview
A fibre link either closes inside its loss budget or it does not, and the difference is often a few tenths of a dB spread across connectors, splices and kilometres of cable. The budget comes from a physical inventory: feeder, distribution and drop segments with their own attenuation at the operating wavelength, a mix of APC and UPC connectors, fusion and mechanical splices that behave quite differently, and perhaps a PON splitter that takes a large share on its own. Adding it up by hand is slow and easy to get wrong.
The calculator builds the budget the way the plant is built. Each fibre segment has its own length and attenuation, filled in from the selected fibre type and wavelength and editable when you have cable data or OTDR results. Connectors are entered by type and number of mated pairs at the TIA-568.3-E maximum of 0.75 dB, and fusion and mechanical splices are counted separately at 0.30 dB, each editable with manufacturer or measured values. An optional PLC splitter adds the ITU-T G.671 maximum insertion loss for the chosen split ratio, or the manufacturer's figure.
The total link loss is compared with the maximum allowable loss less any ageing and contamination allowance you enter, and the design margin passes at 0 dB or more, or is flagged when it falls under a target you set. No standard gives a value for the allowances or the target, so they are blank by default. A worst-case link return loss is calculated from the TIA minimum return loss of every connection and splice, and the limiting item is named. When a multimode fibre is selected at 850 nm, the span and link loss are also checked against IEEE 802.3 short reach Ethernet limits, because modal dispersion can limit reach even when the loss budget closes.
Build the fibre plant from any number of labelled segments, each with its own length and attenuation. Choosing a single-mode or multimode fibre type and a wavelength fills in the cable maximum attenuation from ITU-T G.652, G.657 or TIA-568.3-E, which you can override with cable or OTDR data.
Enter each connector type, from LC and SC to MPO and E2000, with its number of mated pairs. The TIA-568.3-E maximum of 0.75 dB per mated pair is filled in and can be replaced with manufacturer or measured values, and the TIA minimum return loss follows the polish and fibre type.
Fusion and mechanical splices are counted separately, each with its own loss per splice, defaulting to the TIA-568.3-E maximum of 0.30 dB. Both are counted in the worst-case return loss at the TIA splice minimum.
Add a PLC splitter for PON and FTTH links and choose a split ratio to use its ITU-T G.671 maximum insertion loss, or type the manufacturer's figure. G.671 has no 1:128 value, so that ratio needs a typed figure.
The maximum allowable loss less any ageing and contamination allowance gives the effective budget. ITU-T G Suppl. 39 asks for a margin but gives no value, so the allowances and the margin target are optional and blank by default. Where the link standard sets a minimum channel loss, the link is checked against it in the worst case too, and flagged for measurement when that cannot be shown.
The worst-case link return loss sums the reflectance of every connection and splice at its TIA minimum: 35 dB single-mode from TIA-568.3-D (26 dB in TIA-568-C.3) and 20 dB multimode from TIA-568-B.3. Single-mode APC is taken at 55 dB, a labelled assumption from the TIA CATV value. The item that limits it is named.
For OM3, OM4 and OM5 fibre at 850 nm, the span and link loss are compared with the IEEE 802.3 operating range and channel insertion loss for short reach Ethernet at each data rate, as reproduced by the TIA Fiber Optics Technology Consortium. These PHYs run at 850 nm, so the check is not made at other wavelengths. A link can pass the loss budget and still be too long for the data rate.
Link standard budgets for common Ethernet and PON classes, such as 1000BASE-LX and GPON Class B+, set the sourced budget, any minimum loss, fibre and wavelength in one step, and preset scenarios load example designs. Results copy to the clipboard as a text summary that lists the standards used.
Inputs and outputs
Inputs 10
Outputs 10
Use cases
It is built from the physical inventory rather than a single class figure. The tool adds the loss of every fibre segment (length times attenuation at the selected wavelength), every mated connector pair, every fusion and mechanical splice and the optional PLC splitter. The total is compared with the effective budget, and the difference is the design margin.
The maximum allowable loss is the figure set by the system or link standard, and its source is shown beside it. The effective budget is that figure less any allowance you enter for ageing of the plant and for connector contamination. No standard gives them a value, so they are blank by default.
The tool takes the TIA minimum return loss of every connector pair and splice (35 dB single-mode from TIA-568.3-D, 26 dB in the earlier TIA-568-C.3, and 20 dB multimode from TIA-568-B.3, with single-mode APC at 55 dB as a labelled assumption from the TIA CATV value), converts each to a linear reflectance, adds them together and converts the sum back as −10 log₁₀ of the total. It is a worst case: measured connections are usually better. The item that limits the result is named.
The defaults are the TIA-568.3-E maxima: 0.75 dB per mated connector pair and 0.30 dB per fusion or mechanical splice. Each one is tagged in the inputs, and you can replace it with a manufacturer or measured value, which is then tagged as typed.
It appears when OM3, OM4 or OM5 fibre is selected, and runs at 850 nm, the wavelength of these PHYs. The total span and link loss are compared with the IEEE 802.3 operating range and channel insertion loss for short reach Ethernet at each data rate, and any rate the link is too long or too lossy for is flagged. Modal dispersion limits multimode reach independently of the loss budget, so a link can pass one check and fail the other.
The splitter uses the ITU-T G.671 maximum insertion loss for the chosen split ratio, and the minimum channel loss check uses the worst case: the G.671 minimum splitter loss with fibre, connectors and splices at 0 dB, because no standard gives them a minimum. Type the manufacturer's figure to override it. G.671 has no 1:128 value, so that ratio is not assessed until a figure is typed.
Yes. Choose a link standard to set the budget, fibre type and wavelength for a common Ethernet or PON class, then enter the vendor's fibre, connectors, splices and splitter and read the margin. The copied summary lists the standards used, ready for a design pack or commissioning record.
No. The calculations run in your browser, and your design is kept in your browser's local storage so it is there on your next visit. Nothing you enter is sent to a server.
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