Tim's blah blah blah

Coupling my fiber internet directly into my router

(Updated: )

I have FttH which we use for our internet. Because I can, I replaced our NTU (Network Termination Unit) that converts optical to electrical signals, and directly coupled the fiber into my MikroTik router. Here I summarise my findings for my own record and hopefully to help others. Among other things, I cover TX/RX wavelengths, fiber ends, fiber connectors, SFP compatibility, transceivers, and DHCP & VLAN settings.

Theory

Nomenclature

Wavelengths

Our internet (sput.nl) uses one fiber with two wavelengths, meaning there are different wavelengths for upstream and downstream data. This asymmetry means you have to pick the right transceiver on your end. In our case, I use a 1310nm-TX/1550nm-RX transceiver (fs.com) . Note that 1490nm RX wavelength is also mentioned occasionally, but the photodiodes used for receiving are rumoured to be sensitive to both 1490nm and 1550nm light.

Fiber ends

There are different ways fiber tips are polished (ppc-online.com) to reduce signal loss of fiber-to-fiber connections (fiberopticshare.com) . There are two main flavours: flat fiber tips (PC, UPC, with blue connectors) and angled fiber tips (APC, APC8, APC11, with green connectors). Angled fibers are superior, but orientation sensitive, which is taken care of by the connector.

Fiber connectors

There are different physical optical fiber connectors (wikipedia.org) . Main types are FC, LC, and SC. A cable can have different connectors on either side.

Fiber modality

Fibers an be single mode (wikipedia.org) or multi mode. In my case I need a single mode fiber (SMF).

Hardware

Transceivers

A transceiver in this context translates optical signals to electrical signals and vice versa. It has to combine all previously mentioned parameters in one device:

I bought mine on fs.com selecting ‘SFP transceivers’ (fs.com) , filtering on 1G BiDI SFP (fs.com) , then on max 20km distance (fs.com) , and finally selecting the right wavelengths: 1310nm TX and 1550nm RX (fs.com) .

Fiber

In my case the transceiver has an LC simplex connector (fs.com) and the FTU has an SC connector. The fiber end on both the transceiver and the FTU end are blue, and hence I need a UPC fiber tip. Finally, I need a single mode fiber (SMF) for this type of data. In the end, this gives me an LC-SC UPC Simplex Single Mode Fibre Patch Lead 2.0mm (fs.com) fiber.

Software

Once the hardware level is in order, with my fiber connection I needed the following software settings:

Mounting

Below I describe the steps to physically mount the fiber. The SFP simply plugs in the router, the NTU/FTU is more tricky. Also see these videos of connecting the fiber to FTU (youtu.be) , FTU & NTU mounting (youtu.be) , and these various video of mounting NTU/fiber modem (fiber.nl)

To de-mount the NTU, there’s a clip on the top of the box:

After sliding it open, and removing the NTU (ZTE in my case), you have the bare FTU:

I took the NTU, opened it, and removed the PCB:

In the empty NTU I connected the fiber to one side of the connector, the other end is ready for the SFP transceiver:

After connecting the fiber to the empty FTU, I slid it back on the NTU and connected it to my router:

Sources

#Linux