Single-mode or multi-mode is decided by the optics, not the distance you are covering

This is the one choice that goes wrong most often. The cable has to match the transceivers at both ends: OS2 single-mode pairs with single-mode optics, OM3, OM4 and OM5 multi-mode with multi-mode optics. They are not interchangeable, and a multi-mode lead between two single-mode transceivers will either not link at all or link and behave unpredictably. Multi-mode optics are cheaper and suit runs inside a building; single-mode carries further and is the usual answer between buildings. The jacket colour is the fastest way to identify what you already have — yellow is OS2, aqua is OM3, violet OM4 and lime green OM5.

Connector type and polish

LC is the modern duplex connector and the majority of what is here. SC is larger and still common on older switches, media converters and building infrastructure. ST turns up on legacy multi-mode. MPO and MTP are multi-fibre trunks used for 40G and 100G parallel optics and for breakout to four separate links. Polish matters as much as the connector: UPC ferrules are blue, APC are green and angled to reduce back reflection on single-mode. Do not mate APC to UPC — the geometries do not meet, the loss is high, and you can damage the end faces.

Inside a rack, a DAC or AOC is often the cheaper answer

For a switch-to-server hop of a few metres, a direct attach copper lead with the transceivers already fitted costs less than two optics plus a patch cable, and draws less power. Active optical leads do the same job over longer distances. Both are usually coded for a particular switch vendor, so check compatibility against the equipment rather than the speed alone. Where a building is occupied, specify an LSZH jacket.

Brands

Microconnect, Mercodan, Lanview and Ubiquiti, alongside fibre and direct attach leads from Cisco, HPE, StarTech.com, AddOn Networks, Lindy, NVIDIA and MikroTik.

Trade pricing and business accounts are available for UK organisations, and bulk orders are welcome — request a quote.