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lapsio
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What is exactly direct attach cable?... Does it contain SFP+ interface?

Thu Jan 12, 2017 8:46 pm

Hello

I ordered CCR1009 and I'm planning to connect it to CSR using 10g SFP+. So I also ordered 2x S+85DLC03D and 1m direct attach sfp+ cable. Because well I thought it's CABLE I can plug into those S+85DLC03D as name says. But... I see that there's 1m/3m DAC on SFP comparibility list and... I think I just really screwed up?...

Wait are those 1m/3m just 1m optical cables or they're sold as set 2x SFP+ interfaces with integrated cable? Did I just unnecessarily buy two S+85DLC03D? :(
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Fri Jan 13, 2017 4:35 am

That's right, the DAC has built in SFP+. I'm sure you could sell the S+85DLC03D's on eBay, or hold onto them for another job.
 
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lapsio
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Fri Jan 13, 2017 4:47 am

I think it would be nice if MTK would explicitly mention that package includes SFP+ interfaces. At least in brochure or somewhere deeper. I mean well I know I could be more careful with shopping but still for people new in this topic it's not that obvious and photos usually show products with some additional "not included" stuff so I thought it's also the case here. And I'm pretty sure for many people MikroTik devices are first serious gear they ever get because it's just affordable for home lab so I think instructions should be possibly clear and straightforward.

Welp. Happens.
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Fri Jan 13, 2017 5:26 am

I think it would be nice if MTK would explicitly mention that package includes SFP+ interfaces. At least in brochure or somewhere deeper. I mean well I know I could be more careful with shopping but still for people new in this topic it's not that obvious and photos usually show products with some additional "not included" stuff so I thought it's also the case here. And I'm pretty sure for many people MikroTik devices are first serious gear they ever get because it's just affordable for home lab so I think instructions should be possibly clear and straightforward.

Welp. Happens.
i think this is common to all hardware manufacturers.. i guess they assume that all who purchase are familiar with the DAC or have handled DAC cables before.
happened to me with HP gear. sometimes, we learn the hard way.
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Fri Jan 13, 2017 9:36 am

To make it explicit: DAC cable is not optical cable, but copper cable.
 
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lapsio
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Fri Jan 13, 2017 10:19 am

To make it explicit: DAC cable is not optical cable, but copper cable.
:o

Is S+85DLC03D faster then (lower latency)? Or it makes no difference on such short distance? Or higher latency because of optical signal generation overhead?
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Fri Jan 13, 2017 10:24 am

first of, here is the link to the product:
https://routerboard.com/SplusDA0001
as you can see, it is an interface with directly attached cable (hence DAC)

Also, it is listed under the interfaces menu, not accessories.

At such a short distances - it does not matter.
 
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lapsio
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Fri Jan 13, 2017 5:11 pm

Sorry, I tried really hard to not ask "lazy questions" but I'm googling for hours, reading dozens of optical patchcords guides and I still have no idea which parameters of cable matter. For now I know that I need:
  • LC-LC
    multi mode
    duplex
Patchcord, possibly good quality (OM2/3 means good right?).

Is there anything else I should look for to get 10G? I found this cord in local store:

https://www.cyberbajt.pl/produkt/7823/p ... uplex.html

Is it okay? I tried looking for 850nm but most shops don't mention wavelength so I'm a bit confused.
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Fri Jan 13, 2017 9:49 pm

...
Is it okay? I tried looking for 850nm but most shops don't mention wavelength so I'm a bit confused.
It's ok for S+85DLC03D but why don't you use the DAC ?
 
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Sat Jan 14, 2017 11:14 am

...
Is it okay? I tried looking for 850nm but most shops don't mention wavelength so I'm a bit confused.
This is because the wave length is irrelevant to the patch chord.
If the connector fits, and it is the correct single mode (SM) or multi mode (MM) fiber, it will work on all wave lengths.
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lapsio
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Sat Jan 14, 2017 12:51 pm

...
Is it okay? I tried looking for 850nm but most shops don't mention wavelength so I'm a bit confused.
It's ok for S+85DLC03D but why don't you use the DAC ?
I must say It was quite disappointing to hear that DAC is copper :< Because I really wanted to use optical interface for the first time in my life :D Also well S+85DLC03D isn't really that expensive. I don't feel like I bother to sell/return them. Plus I guess now I more or less understand optical cables basics so there's always educational value and it's home lab after all.

So I guess I'll just try both, try to benchmark latency (I heard some urban legends long time ago from friend admin that optical/active short distance connections may suffer higher latency than passive ones because there's one more layer) because I'd like to use it for SSD NAS. If there won't be absolutely any difference in random i/o I guess I'll just use one as 1.25g link to RB2011 replacing current gigabit and another one between switch and CCR1009 for now.

Thanks for help everyone :)
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Sun Jan 15, 2017 4:11 am

DAC cables, although copper, are rated to the speed required to operate without the complexity of having to understand optics.

on that note, there are two kinds of fiber optic cables to use.. multi-mode and single-mode. the SFP to use should match the cable as well. the major difference between the two being price and range of operation -- single-mode is more expensive and has longer range.
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Sat Jan 28, 2017 8:50 pm

There's also a product called "active optical cable" which is a cable, usually uniaxial single mode fiber with a permanently attached pair of transceivers. It's hard for me to see the appeal of such a product over just getting a pair of SFP/SFP+/QSFP+ transceivers, and a pre-terminated lc-upc/lc-upc smf cable.
 
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lapsio
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Sat Jan 28, 2017 9:11 pm

There's also a product called "active optical cable" which is a cable, usually uniaxial single mode fiber with a permanently attached pair of transceivers. It's hard for me to see the appeal of such a product over just getting a pair of SFP/SFP+/QSFP+ transceivers, and a pre-terminated lc-upc/lc-upc smf cable.
I'd say it's easier to pull out such cable comparing to conventional transceiver and safer bc you don't need to remove patchcord from interface thus you don't need to care about laser exposure. However according to my experience of removing DAC with screwdriver bc latch seemed to be broken It's hard for me to say that they are indeed easier to remove :/...
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Thu Feb 02, 2017 11:44 am

DAC cables are usually the best option for the very short distances, unless electrical isolation matters.
It is much simpler (less electronics). They use less energy than fiber and much less than UTP.
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Re: What is exactly direct attach cable?... Does it contain SFP+ interface?

Wed Oct 17, 2018 9:49 am

Yes, DAC cable is a form of the high-speed cable with “transceivers” on either end.

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