The FTTx link, end to end
Every FTTx architecture – FTTH, FTTB, FTTC – is the same chain with the fiber stopped at a different point. The active equipment at the two ends is what changes between projects. The middle is passive, and it is the middle that lasts.
The signal starts at the OLT in your exchange or central office, where one PON port feeds a feeder cable. That feeder reaches an optical splitter – an unpowered PLC device that divides the light into 2, 4, 8, 16, 32 or 64 branches. The split output continues as distribution cable to a street cabinet or a building riser, terminates in a distribution box or a splice closure, and the last leg to each subscriber is a drop cable, normally a 2-core or 4-core bow-type indoor or self-supporting outdoor cable. At the far end sits the ONU or ONT, which converts the light back to Ethernet and the subscriber’s other interfaces.
Two wavelengths travel down the same strand in opposite directions. In GPON, downstream is 1490 nm and upstream is 1310 nm, with an optional 1550 nm window reserved for RF video overlay. XGS-PON deliberately moves to 1577 nm downstream and 1270 nm upstream so that it can share the same fiber and the same splitters as GPON. That non-overlap is the entire basis of a phased upgrade, and it is worth real money: you replace OLT cards and subscriber terminals on a schedule, and leave the outside plant alone.
Figure 1 — The FTTx link from the OLT to the subscriber. The middle of the chain is passive, standardized and bought direct. The two ends are active and tied to the PON standard you freeze.
The PON generations, and why you cannot mix them
The standard you choose decides the wavelengths, the split you can afford, the ONU you can order, and whether your existing plant can be reused. Choose it before you choose any hardware.
| Standard | Body and reference | Down / up per PON port | Downstream / upstream wavelength | Typical split | Optical budget class |
|---|---|---|---|---|---|
| GPON | ITU-T G.984 series | 2.488 Gbps / 1.244 Gbps, asymmetric | 1490 nm / 1310 nm | 1:32 to 1:64 | Class B+ 28 dB, Class C+ 32 dB |
| EPON | IEEE 802.3ah | 1.25 Gbps / 1.25 Gbps, symmetric | 1490 nm / 1310 nm | 1:32, up to 1:64 | PX20, roughly 24 dB |
| 10G-EPON | IEEE 802.3av | 10 Gbps / 10 Gbps symmetric, or 10 / 1 Gbps | 1577 nm / 1270 nm | 1:32, up to 1:64 | PR30, roughly 29 dB |
| XG-PON | ITU-T G.987 series | 10 Gbps / 2.5 Gbps, asymmetric | 1577 nm / 1270 nm | 1:64 | N1 29 dB, N2 33 dB |
| XGS-PON | ITU-T G.9807.1 | 10 Gbps / 10 Gbps, symmetric | 1577 nm / 1270 nm | 1:64 and beyond | N1 29 dB, N2 33 dB |
The split column is a budget decision you make later, not a property of the standard. The same standard serving 32 subscribers per port and 64 subscribers per port is the same OLT with a different splitter in the cabinet.
GPON and XGS-PON share an ODN because their wavelength bands do not overlap, and they are combined at the OLT with a wavelength multiplexer. EPON uses Ethernet framing rather than GEM/GTC, so an EPON ONU will not register on a GPON or XGS-PON port and vice versa, regardless of what the connectors look like. The practical consequence: pick the standard once, and write it into the specification as a frozen requirement, not as a preference.
Which half of this chain you should buy direct
There are three supply routes in the chain above, and they behave completely differently on price and on lead time.
| Link | What it is | Normal supply route | Why it behaves that way |
|---|---|---|---|
| OLT | Active, in your exchange | PON vendor, tied to the standard | Proprietary management, firmware and support contract. Not a commodity purchase. |
| Optical splitter | Passive, in the street or riser | PON vendor’s accessory list, or open market | Class and spectral response matter; the split ratio has to be decided against your budget. |
| ONU / ONT | Active, at the subscriber | PON vendor, certified against your OLT | Must be accepted by the OLT, and its feature set is what your subscriber actually sees. |
| Feeder and distribution cable | Passive, in duct or on pole | Open market, optical for a direct-purchase decision | Standardized fiber and construction. The differentiator is construction quality and lead time, not protocol. |
| Distribution box, terminal box, ODF | Passive, in cabinet or riser | Open market, direct purchase | Mechanical, standardized, and bought by the thousand. Distribution margin is the only thing that moves the price. |
| Drop cable and patch cords | Passive, to the subscriber | Direct purchase, always | Consumable volumes with no proprietary content. This is a pure unit-price and consistency question. |
| Optical modules | Pluggable, in every SFP cage | Direct purchase for volume, coded to platform | MSA hardware is generic; only the EEPROM coding is platform-specific. |
ONU or ONT: the difference, and the seven things to freeze
This is the most-searched question in the whole topic and the answer is shorter than most pages make it. ONU and ONT refer to the same functional device: the subscriber end of the PON, the thing that converts light to Ethernet. The difference is normative and positional, not functional.
ONT – optical network terminal – is the ITU-T term, and the ITU-T defines it as a single-subscriber device, which is why GPON documentation uses it for the box on the customer’s wall. ONU – optical network unit – is the IEEE term used in EPON documentation, and it is also the general term for a device serving more than one subscriber from a shared position, such as a building riser or a technical room. In commercial practice the two words are used interchangeably, and a device sold as a GPON ONU is normally functioning as an ONT. The distinction matters in exactly two places: when you are writing a specification that has to be unambiguous, and when you are checking whether a multi-subscriber unit differs from a single-subscriber unit in ways your build cares about.
| Form factor | Typical position | Function | Order it when |
|---|---|---|---|
| SFU – single family unit | Single home | Optical-to-Ethernet conversion only, usually 1 GE port, no routing or Wi-Fi | The subscriber supplies their own router, or you are selling a bare bitstream |
| HGU – home gateway unit | Single home | Integrated ONT, NAT router, DHCP, Wi-Fi, VoIP ports, sometimes CATV overlay | You are delivering a finished residential service under your own brand |
| MDU – multi-dwelling unit | Building riser or technical room | Serves several homes or offices over the existing in-building cabling; typically 8 or 16 ports | You are wiring an apartment block and want one device instead of eight or sixteen |
| SBU / MTU | Business park or small enterprise | Enterprise routing and QoS, multiple VLANs, SNMP or TR-069 management | You are selling to business tenants with an SLA attached |
What actually needs to be frozen in the specification, and in this order:
1.The PON generation. GPON, XGS-PON or EPON, stated as a requirement and not as a range. This is the decision that everything else depends on.
2.The optical class of the OLT port and the ONU. Class B+, C+ or the XGS-PON N1 / N2 equivalent. If the two ends differ, the lower one sets the budget.
3.The subscriber interfaces. Port count and speed on the Ethernet side, whether Wi-Fi is in scope, whether there are POTS ports for legacy telephony, and whether a CATV overlay port is needed. This is what the subscriber experiences.
4.The management protocol. TR-069 or OMCI, and which of the two your OSS actually speaks. Discovering this at commissioning is expensive.
5.Temperature and enclosure. An ONT indoors and an ONU in an unconditioned street cabinet are different products. If the unit sits outdoors, specify the enclosure and the temperature range as part of the same line item.
6.Power and battery backup. Subscriber-side power is the subscriber’s problem until the phone stops working during a mains outage. If you sell telephony, decide early whether backup is provided and by whom.
7.Firmware and upgrade policy. Who can push firmware, how often, and whether a failed upgrade is recoverable remotely. This is the largest hidden cost in a large ONU estate.
The passive half: distribution boxes, drop cable and ODF
The passive plant is the part of an FTTx build you construct once and then live with. The OLT is a purchase order every five to seven years; the ONU estate turns over every three to five. The fiber in the duct, the splitter in the street cabinet and the box on the pole are the 20-year assets, and they are also where a large share of the build cost sits. Two consequences follow, and they both point the same way.
First, quality decisions here are permanent in a way that active-equipment decisions are not. A connector that was not cleaned, a splice that was not documented, a distribution box that filled with water – none of these can be fixed by a firmware release. Second, because the parts are standardized and bought in volume, this is the half where direct purchase from the manufacturer changes the arithmetic most, and where a supply problem has the least schedule slack to absorb it.
Distribution boxes and splitter housings
The box that holds the splitter or the splice is chosen by core count, mounting and environment, and it is one of the few places where a small specification error is expensive to undo: the enclosure is sized to the street cabinet, the pole bracket or the riser, and changing it later means re-entering the customer’s building. PX-type distribution boxes cover 12 to 144 cores, which is the range that covers a street cabinet feeding a residential block through to a riser serving a large building.
Drop cable
The drop cable is the least glamorous item on the bill of materials and the one that generates the most truck rolls. It is bent, stapled, pulled around corners and terminated by hand in an apartment, so its mechanical behaviour matters more than its optical behaviour. Bow-type indoor drop cable and self-supporting outdoor drop cable are the two constructions; the outdoor version carries its own strength member so it does not need a messenger wire. Bend-insensitive single-mode fiber is what allows the tight radii a real building imposes, and it is the single most useful thing to specify on this line.
Patch cords, pigtails and ODF
Inside the exchange and inside every street cabinet, the fiber has to be terminated, presented and recorded. The optical distribution frame is the interface between the outside plant and the equipment: it holds the adapters, protects the splices, and gives the field team a documented end to every strand. Rack-mount ODF frames run from 12 to 144 ports and are compatible with splice trays, which matters because the tray is where the actual loss is introduced – 0.05 to 0.1 dB per fusion splice, against roughly 0.2 to 0.5 dB per mated connector pair. Both figures are small individually and both add up across a link, which is why the frame and the tray should come from the same supplier as the cable.
| Position in the link | What you order | Range we build | What to state on the enquiry |
|---|---|---|---|
| Street cabinet or splice point | PX-type fiber distribution box | 12 to 144 cores | Core count, mounting (pole, wall, cabinet), and whether a splitter module is housed inside |
| Building riser or technical room | GHQ-series termination box | 4 and 8 port wall-mount; 12, 24 and 48 port rack-mount | Port count, mounting, and connector type (LC, SC, ST or FC) |
| Exchange or equipment room | Rack-mount ODF | 24, 48, 72, 96 and 144 ports | Port count, rack unit height, adapter type, and splice tray capacity |
| Splice closure | 300-type splice tray | 12 ports, LC / SC / ST / FC | Fiber count per tray and the closure it has to fit |
| Every termination | SPQ-series adapter | LC duplex; SC, ST and FC simplex | Connector type and whether simplex or duplex |
| Subscriber drop | Bow-type indoor drop cable | 2-core and 4-core, length to order | Core count, length, whether pre-terminated, and the bend radius the route imposes |
| Feeder and distribution | Outdoor single-mode cable | Central loose tube light-armored (GYXTW); stranded armored flame-retardant (GYTS / GYTA); GJFJV indoor, 2 to 128 fibers | Core count, construction (duct, aerial, direct-burial), and span |
| Equipment patch | Single-mode and duplex patch cords, plus pigtails | LC / SC / FC / ST, simplex or duplex, 0.5 to 1000 m, custom lengths | Connector pairing, length, fiber type and polish |
The cable range carries 47 products in stock and the accessories range carries 34. Core counts and mounting styles that are not on the shelf are built to order, and every batch ships with its CE, FCC and RoHS certificates.
Optical modules and media converters: compatibility and bulk buying
Optical modules are the one line item that appears at both ends of the chain you saw earlier: in the OLT’s uplink cages, in the switches in your backhaul and aggregation, in media converters in cabinets that have no switch, and in the OLT’s own client-facing ports on some architectures. That is why they deserve their own line in the budget rather than being absorbed into “active equipment”.
Four numbers, and a fifth spec
A module part number is fully determined by four things: the rate the port negotiates, the package that matches the cage, the reach the link needs, and the fiber you already have in the ground. That last one decides more than people expect, because a single-fiber bidirectional (BiDi) link uses a complementary wavelength pair – one end transmits where the other receives – and the pair has to be ordered as a pair.
| Dimension | Options in our range | What decides it |
|---|---|---|
| Rate | 155 Mbps, 1.25 Gbps, 2.5 Gbps, 10 Gbps, 25 Gbps, 40 Gbps, 100 Gbps | The highest rate the port and the service require, not the highest the module can do |
| Package | SFP, SFP+, SFP28, QSFP+, QSFP28 | The cage. A 10G port runs a 1G module; a 1G port cannot run a 10G module. SFP28 negotiates at 10G in an SFP+ cage. |
| Reach | Dual-fiber multimode 2 and 5 km; dual-fiber single-mode 20, 40, 60, 80, 100 and 120 km; single-fiber single-mode 20, 40, 80, 100 and 120 km | Distance plus the loss of the connectors and splices on the way, plus a safety margin |
| Fiber | Dual-fiber single-mode by default; single-fiber BiDi on request; CWDM and DWDM channels for fiber-constrained routes | How many strands you have, and whether the route is fiber-poor |
| Temperature grade | Commercial 0 °C to +70 °C; extended −10 °C to +80 °C; industrial −40 °C to +85 °C | Whether the module lives in an air-conditioned room or in a street cabinet |
Figure 2 — Four numbers fix the part number of an optical module. The fifth specification, the EEPROM coding, decides whether your switch will accept it.
The four compatibility questions that cause returns
Compatibility is where bulk purchases go wrong, and almost always for a reason that has nothing to do with optical performance. An SFP is physically and electrically standardized by the MSA, and its diagnostic interface is defined by SFF-8472. What is not standardized is the firmware conversation between the module and the host. A router or switch reads the module’s EEPROM before it enables the port, and if the identity fields are not what that platform expects, the result ranges from a log warning through to a port that stays down.
| Question to settle before ordering volume | Why it changes the order |
|---|---|
| Which exact host platforms will these modules go into – make, model and firmware version? | The EEPROM coding has to match the platform. “Cisco-compatible” is not a specification; a model and a firmware train is. |
| Does the platform enforce module validation, and does it warn, restrict diagnostics, or keep the port down? | Determines whether a coding miss is an annoyance or an outage, and therefore how much of the batch needs to be tested first. |
| Will digital optical monitoring be visible on your NMS? | Modules that are accepted but that do not report Tx / Rx power and temperature blind your fault-finding. Get this confirmed rather than assumed. |
| Is the wavelength pair correct end to end on every BiDi link? | A BiDi link with two modules of the same side transmits into a receiver on both ends and links nowhere. This is the single most common BiDi mistake. |
The honest way to buy in volume is to ask for a pilot batch, put it into the platforms you actually run, and read the transceiver inventory from the switch rather than trusting the label. That is also what makes a factory-direct order safe: the coding is a manufacturing step, not a stock item, so it is set for the platform you name. Our converter and module range is coded for the switch brands your network already runs, in SFP, SFP+ and BiDi form factors, with every unit tested before it ships.
Where media converters still earn their place
A media converter does one job: it takes Ethernet on copper, puts it on fiber, and does the reverse at the far end. It is the wrong answer when the far end needs more than one device, when traffic has to be separated, or when you want remote diagnostics – those are switch jobs. It is the right answer in a lot of ISP cabinets, where a single device needs a fiber uplink and there is no room, no power budget and no management network for a switch.
| Model | Ports | Rate | Fiber side | Notes |
|---|---|---|---|---|
| wsCom1000-1GST-2G/DC-INT | 1 fiber + 2 RJ45 | 1000 Mbps | 1×9, ST / FC / LC; dual-fiber by default, single-fiber 1310 nm / 1550 nm optional | DC 12–57 V, DIN-rail, −20 °C to 65 °C |
| wsCom1005-1GST-4G/DC-INT | 1 fiber + 4 RJ45 | 1000 Mbps | 1×9, ST / FC / LC | Aluminium housing, 4 kV surge protection, supports PoE power supply |
| wsCom3010-2GST-8G/DC-INT | 2 fiber + 8 RJ45 | 1000 Mbps | SFP slot, module not included | The step up when a cabinet serves several devices on one uplink |
| WS105-2TXST-4TX/DC-INT | 2 fiber + 4 RJ45 | 100 Mbps | ST / FC / LC | Commercial carrier-grade series for indoor cabinets |
| WS1005-2GESFP-4GE/DC-INT | 2 fiber + 4 RJ45 | 4 × 2.5G / 1G RJ45 + 2 × 10G SFP+ | SFP+ slot, module not included | PoE+ 802.3at, 3-level surge protection, external DC 12 V adapter |
Two ordering points that catch people out on industrial models: the SFP modules are sold separately on the models with SFP slots, and the power adapter is not included by default. State both on the enquiry so the quote is complete.
Cost structure: what buying direct from the factory changes
Take any line in an FTTx bill of materials and trace what is inside its landed cost. There are six layers, and the difference between a channel purchase and a factory purchase is which of them you keep paying for.
| Layer in the landed cost | What it pays for | Channel purchase | Factory-direct purchase |
|---|---|---|---|
| Factory cost | Components, housing, assembly, test | You pay it, plus everything below | You pay it |
| Coding and configuration | Platform-specific EEPROM coding, labelling, batch traceability | Absorbed invisibly into the channel price | A stated step, quoted per platform and per quantity |
| Certification and documentation | CE, FCC, RoHS batch certificates, test records | Provided, but rarely with the factory record | Provided with the batch |
| Freight and clearance | Movement from the factory to your border | Bundled and invisible | Yours, and visible, so you can choose the mode |
| Import duty and local charges | Border charges in your country | Yours either way | Yours either way |
| Channel margin and local stock | Distributor margin at each tier, warehousing, local availability, warranty handling, small-quantity premium | The largest discretionary layer. Two tiers means two margins. | Removed – and replaced by your own stock, handling and warranty process |
Three things follow from that table, and they are the whole of the argument. First, the layers you remove are real money at volume, because a two-tier channel on a commodity line carries two margins plus the cost of holding stock locally. Second, the layers you add back are yours to control: freight mode, consolidation across a mixed container, and your own incoming inspection. Third, the layers that do not change – duty and local charges – are the same either way, which is why the percentage you save is never the same as the percentage of the channel margin.
So work the arithmetic on your own numbers rather than on a headline percentage. For each line, take the channel unit price, subtract the factory unit price, subtract whatever the direct route adds for coding and freight and inspection, and divide by the channel unit price. On high-volume passive parts – drop cable, patch cords, distribution boxes, adapters – that normally gives the largest number, because the part is fully standardized and both channel margins are pure overhead. On OLT and ONU the arithmetic does not apply at all, because those are not commodity purchases. On optical modules it lands well above the passive parts on unit price and somewhat below them on percentage, because coding is a real cost that a channel absorbs but a factory quotes. Across a mixed FTTx bill of materials at wholesale volume, a planning range of 30 to 40 percent below a two-tier channel cost is a reasonable target to work to; whether a particular line reaches it depends on volume, HS classification and freight, and we would rather show you the layers than defend a single number.
What direct sourcing does not remove
· Freight and duty. They move from invisible to visible, not to zero. Plan the landed cost, not the ex-works price.
· Your own incoming inspection. A distributor’s local stock is also a buffer against the batch you would otherwise have to check yourself. Budget for the check.
· Spares and warranty logistics. If a module fails, the replacement comes from your shelf or by air from ours. Either way, someone carries it.
· Lead time versus availability. A local distributor sells what is on the shelf today. A factory sells what it builds next. Faster and cheaper are different decisions, and on long-lead passive parts the schedule matters more than either.
· Minimum order quantities. Factory pricing assumes a volume that justifies a production run. Below that, the channel price may genuinely be the better one.
Send us the bill of materials
Quoting an FTTx package without a specification is how both sides waste a week. A bill of materials we can price in one pass carries six things: the item, the quantity, the technical parameters that fix the part number, the destination, the certificate or standard the project requires, and the date it has to be on site. If you have a spreadsheet, send the spreadsheet.
| Line type | The parameters we need to quote it exactly |
|---|---|
| Optical module | Rate, package, reach, fiber type (dual-fiber or single-fiber, and which side of a BiDi pair), temperature grade, host platform with firmware version, quantity, connector. |
| Media converter | Fiber port count and type, RJ45 port count, rate, whether PoE output is needed, input voltage, mounting, temperature, quantity. |
| Drop cable and patch cords | Core count, construction (indoor bow-type or self-supporting outdoor), connector pairing, length, whether pre-terminated, quantity. |
| Feeder and distribution cable | Core count, construction (duct, aerial, direct-burial), span, jacket requirement, quantity. |
| Distribution box, termination box, ODF | Core or port count, mounting, connector type, rack unit height for ODF, splice tray capacity, quantity. |
| Splice trays and adapters | Type, port count, connector type, simplex or duplex, and the closure or frame they must fit, quantity. |
An engineer reads the list, tells you where the specification is ambiguous, and sends a written quote within 24 hours. If a line we do not build is on the list – OLT, ONU, splitter – we will say so and quote the rest, so you can place one order for the passive half and the modules and keep the active procurement with your PON vendor. Start from the optical transceiver range, the fiber cable range, the fiber accessories range, or send the BOM directly through the contact form. Everything is built in our own factory in Shenzhen; Winsure since 2016, the Hansun group since 2004, with ISO 9001, ISO 14001 and ISO 45001.
Frequently asked questions
1.What is the difference between an ONU and an ONT?
They are the same device in the same place, and the difference is terminology rather than function. Both convert the optical signal at the subscriber end into Ethernet and other interfaces. ONT is the term used in ITU-T documentation, and the ITU-T defines it as a single-subscriber device, so it is the normal word in GPON. ONU is the term used in IEEE 802.3ah (EPON) documentation and is also the general term for a unit serving more than one subscriber, such as a building riser unit. In practice vendors use them interchangeably. When you write a specification, say which PON generation and which form factor you mean, and the acronym stops mattering.
2.Can I use third-party SFP modules in my OLT or my switches?
Physically and optically, yes – SFP, SFP+, SFP28, QSFP+ and QSFP28 modules are standardized by the MSA, and diagnostics follow SFF-8472. The variable is the firmware check the host performs against the module’s EEPROM identity fields. Some platforms accept any MSA module, some log a warning, some restrict diagnostic monitoring, and some keep the port down. That is why the order should name the platform and the firmware version, and why a pilot batch tested in your own equipment is worth more than any compatibility list. Factory coding is what makes volume purchase safe here: it is a production step, so it is set for the platform you specify rather than for a generic market.
3.Single-mode or multimode for a regional FTTx build?
Single-mode, essentially always, for anything that leaves the building. Single-mode OS2 fiber with 1310 nm and 1490 nm optics carries the distances an access network needs – 20 km and beyond – with a loss budget that allows a realistic split. Multimode is a 2 to 5 km option and belongs to short campus or in-building links, where the cost of the optics and the ease of termination can justify it. Mixing them is not possible: 850 nm multimode optics and 1310 nm single-mode optics are not interchangeable, and the fibers themselves are different, so this is a decision to make once at design time. On a single-mode build, use single-fiber BiDi modules where strands are scarce and dual-fiber everywhere else.
4.What split ratio should I choose?
Choose it last, from the budget, not from the subscriber count. Calculate the ODN loss first: fiber attenuation (about 0.35 dB per km at 1310 and 1490 nm on standard single-mode), plus the splitter insertion loss (roughly 14 dB at 1:16, 17 dB at 1:32 and about 20 dB at 1:64), plus connector losses at around 0.2 to 0.5 dB per mated pair, plus splice losses at 0.05 to 0.1 dB each, plus a safety margin of about 3 dB. Compare the total with the class of your optics: 28 dB for GPON Class B+, 32 dB for Class C+, 29 to 33 dB for the XGS-PON N-classes. If the total exceeds the class, reduce the split ratio, shorten the feeder or move to a higher class – in that order, because the first two are cheaper than the third.
5.Do you supply the ONU and the optical splitter?
No, and we will tell you that on the enquiry rather than after you have placed an order. Winsure builds the passive half of an FTTx link and the pluggable modules: fiber drop and distribution cable, PX-type distribution boxes, GHQ termination boxes, rack-mount ODF, splice trays and adapters, and SFP, SFP+, SFP28, QSFP+ and QSFP28 optical modules, plus fiber media converters. OLT, ONU/ONT and optical splitters come from your PON vendor, tied to the standard you have frozen. A mixed bill of materials is normal, and we quote our lines so you can combine them with the active lines from whoever supplies them.
6.What do you need in order to quote an FTTx bill of materials?
Six things per line: the item, the quantity, the technical parameters that fix the part number, the destination, any certificate or standard the project requires, and the required on-site date. For modules, the parameters are rate, package, reach, fiber type and side of a BiDi pair, temperature grade, and the host platform with its firmware version. For cable, they are core count, construction, span and connector pairing. For boxes and frames, they are core or port count, mounting and connector type. Send it as a list or a spreadsheet and an engineer will review it, flag anything ambiguous, and return a written quote within 24 hours.