Comment by Reubachi
6 hours ago
While working for a broadcasting/networking integration gig, we designed, assembled and field-terminated thousands of copper and fibre runs from 1/2 ft to football field lengths.
The amount of time required to terminate a copper cable in the field is seconds, and felt a bit like art. Something about the way it reliably reacted was magical and felt "strong."
Terminating or splicing a fibre cable felt like wrestling a snake covered in melted crayons, and the failure rate was significantly higher across the board. And it wasn't just workmanship, but quality of product, terminating environment, available equipment, misuse by future operators etc.
That said, at a certain point, we as a firm learned that most purchasers would rather the low latency/small footprint of optical/fibre versus copper, maintenece/failure be damned. Though, maybe part of our willingness to push fibre came from knowing that most purchasers would in 1-2 years call us back in to replace the rack terminations with copper :)
> The amount of time required to terminate a copper cable in the field is seconds,
This article is about Direct Attach Copper (DAC) cables which are not something you can field terminate. They use twinax copper and have special modules on the end.
You are thinking about standard RJ45 terminated cabling for 1GBASE-T or 10GBASE-T, which is a different.
> That said, at a certain point, we as a firm learned that most purchasers would rather the low latency/small footprint of optical/fibre versus copper, maintenece/failure be damned.
Direct Attach Copper has slightly lower latency than fiber, but the difference is negligible. Both have significantly better latency than 10GBASE-T through twisted pair cabling.
Yes, thanks. It was confusing me for a second because no, no almost one is terminating twinax in the server room.
I had IT company recommend to me a bunch of fiber cables for a cleanup I was doing. They had about 20 or 30 laser modules we would need, and however much fiber.
When they asked why I planned on doing copper, I told him because each run is three fucking feet.
I’m not sure if they just didn’t realize that’s not what fiber is for or they didn’t know that DAC existed.
There are 2 very different main types of "copper" in this context. Each can break down into more specific subcategories but they have a relatively common general behavior with their primary type.
First there is the BASE-T RJ45 stuff, which it sounds like you might have been working with. At 10G or higher speeds this get relatively power hungry and is not really an advantage over fiber unless you are also delivering PoE or are trying to reuse existing cabling.
This type (DAC) is a special type of pre-made cable assembly which eschews much of the advanced signalling/conversion logic. The upside is the power usage is low (often even lower than fiber) and the cost is dirt cheap. The downside is the lengths are much more limited and it's intended to be preterminated SFP-to-SFP (or the like) cable assemblies instead of modular patching/custom built.
There is indeed a latency difference, usually DAC < fiber < BASE-T, but they are all within a few microseconds (not milliseconds) of each other so you really have to be pressed to care about it (to the point you're looking at specialized low latency switches and paying extra to lay things out in a way which minimizes the number of L2 hops rather than the cost).
> 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?
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.
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.
Doesn't that reduce to RJ45?
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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?
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> That said, at a certain point, we as a firm learned that most purchasers would rather the low latency/small footprint of optical/fibre versus copper, maintenece/failure be damned.
Copper bundles get real thick, real fast: I ran an OneFS cluster for many years, and we had >50 nodes, and all the cables (each node dual-connected) ran to two central switches for backend replications. Rat's nest.
I was very happy when Isilon started officially supporting active optical cable (AOC) on the backend. Really helped with airflow and keeping things tidy.