Comment by myself248
4 hours ago
> it's intended to be preterminated SFP-to-SFP
I wonder why nobody's making field-terminatable DACs for custom lengths. If you've torn one down, they're not exactly complicated inside.
If they existed, would people buy them?
I think the only reason RJ45 termination is an (occasional) thing for short patching is you're also in spec to go 100 meters with it so the tools and materials to do so are already commonly in use.
For passive DACs the range of lengths is so low you can just get away with having 2 or 3 different lengths on hand and never need to worry about it. Active DACs start to be too much to bother with again.
Fiber it's possible, but again really only because you can go kilometers with it rather than because people want to make short patch cables themselves.
DAC cables use twinax. Properly terminating twinax is not easy. It's not as forgiving as twisted pair going into an RJ45.
DAC cables have a limited length range. It's not like 10GBASE-T where you can run the cable hundreds of feet and then put a connector on exactly where you need it. The cables only work at short distances so it's easy to stock the cable sizes close enough to everyone's needs.
Doesn't that reduce to RJ45?
No. It's twin-axial. Think coaxial, but more axial.
Nope. For production, you want to reduce risk and variation. DACs are already available in about 5 sizes up to the max 7m length, why would you terminate any other size in the field?
I did spec a couple of 7m dacs a few months ago to run between two adjacent bays, but normally for more than 2m I'll just drop a SM sfp and run a preterminated fibre cable.
In the field its the armoured fibre on a reel, 100m, 200m, 500m etc, with opticon connectors, or some normal cat5 typically for APs
Some network guys I know prefer fibre even within the rack, just because they don't want the weight and the obstructions in the rack. Apparently more than once the weight of the DACs and the bulk of the cable bundle has caused a problem with NICs.
Personally that surprised me, but I can see where they're coming from.
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