Latency Difference Between AOC and DAC Cables

[am45931472]

Searched all over, cant find the exact answer i'm looking for.

Is there any difference in latency performance in active optical cables (AOC) vs copper direct attach cables (DAC). Alot of posts seem to indicate that their performance is 'similar' or nearly similar but never states the exact difference.

I understand cost and power use / heat but not latency / performance differences.

 

[altmind]

I've seen some reports that DAC is faster than plain fiber. idk how fiber compares to AOC.

https://www.arista.com/assets/data/pdf/Copper-Faster-Than-Fiber-Brief.pdf

 

[am45931472]

I've seen some reports that DAC is faster than plain fiber. idk how fiber compares to AOC.

https://www.arista.com/assets/data/pdf/Copper-Faster-Than-Fiber-Brief.pdf

Yes, I've read that PDF. just doesnt get into AOC vs DAC

 

[Spartacus]

Less than a microsecond of difference between the two, there will be no noticeable difference short of crazy high end stock trading automation stuff. If you're doing this for home, its preference and cost (which is similar as well) the fiber does better for longer distances, the DAC for shorter (<10m) is generally the recommended selection.

 

[am45931472]

Less than a microsecond of difference between the two, there will be no noticeable difference short of crazy high end stock trading automation stuff. If you're doing this for home, its preference and cost (which is similar as well) the fiber does better for longer distances, the DAC for shorter (<10m) is generally the recommended selection.

My suspicion has been that they are indeed "close" but that AOC had to be slower because on some level its still making the conversation between electrical signals and light. I've also seen that cost of AOC can varry wildly so it could be possible to find a good deal making its cost much close to what a passive DAC would normally cost.

 

[Spartacus]

The conversion cost is minute at best, especially with todays transceivers.
DAC are cheapest and my preferred method of connection, but I'm about to move one of my servers upstairs I plan to use fiber for that.
Anything at or above 10m distance fiber will likely be cheaper, the upfront cost for the transceivers is usually the most costly, the cable itself is cheap.

 

[am45931472]

sure. way I see it keep those DAC as short as possible. But what about using AOC as a method of mitigating EMI in a large rack. In that situation I would think AOC even at short distances would have some benefit.

 

[Spartacus]

True, but not often a concern either unless you're in an industrial environment.
(thats also why those DAC cables are so thick, they're pretty heavily shielded)

 

[altmind]

personally for me, there are no use cases for aoc cables. if you need emi resistance or long cable runs, use plain fiber.

 

[oddball]

personally for me, there are no use cases for aoc cables. if you need emi resistance or long cable runs, use plain fiber.

We use them in a dense rack, they're easier to work with vs DAC's, especially at 40GbE. At 10GbE I agree, both cables are about the same diameter.