Optical cable to my PC

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kpfleming

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Dec 28, 2021
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I don't think it's helpful to refer to DACs as 'optical or copper, with pre-terminated transceivers'. DACs are copper only, and don't have transceivers, which is why they can only be used in ports with retimers (if the cable is longer than 1m). For example on the ICX7150-24P only four of the SFP+ ports support DACs.

AOCs *are* a pair of transceivers with an optical cable between them.
 
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Railgun

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Jul 28, 2018
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I don't think it's helpful to refer to DACs as 'optical or copper, with pre-terminated transceivers'. DACs are copper only, and don't have transceivers, which is why they can only be used in ports with retimers (if the cable is longer than 1m). For example on the ICX7150-24P only four of the SFP+ ports support DACs.

AOCs *are* a pair of transceivers with an optical cable between them.
You're limiting the definition to a specific type of cable. A transceiver is a module that both transmits and receives. The switch will 100% depend on a transceiver on the port in question. If at the end of a DAC/AOC the module is NOT a transceiver, then what is it?

Of course only 4 ports of that switch support DACs as only four ports are SFP ports. You can't plug a DAC into an RJ45 port.

Let's take Arista for example...


1000base-bx10-d
1000base-bx10-u
1000base-lx
1000base-sx
1000base-t
100base-lx10
100g-dwdm
100g-dwdm-e
100gbase-ar4
100gbase-ar4n
100gbase-cr4
100gbase-cr4n
100gbase-cr4s
100gbase-cwdm4
100gbase-dr
100gbase-er4
100gbase-erl4
100gbase-fr
100gbase-lr4
100gbase-lrl4
100gbase-psm4
100gbase-sr10
100gbase-sr4
100gbase-srbd
100gbase-swdm4
100gbase-xsr10
100gbase-xsr4
100ge-dwdm2
10gbase-ar
10gbase-cr
10gbase-dwdm
10gbase-dwdm-er
10gbase-dwdm-zr
10gbase-er
10gbase-erbd-d
10gbase-erbd-u
10gbase-erlbd-d
10gbase-erlbd-u
10gbase-lr
10gbase-lrl
10gbase-sr
10gbase-srl
10gbase-zr
200gbase-cr4
200gbase-cr8
200gbase-cr8n
200gbase-cr8s
200gbase-sr4
25gbase-ar
25gbase-arn
25gbase-cr
25gbase-crn
25gbase-crs
25gbase-lr
25gbase-lrl
25gbase-sr
400gbase-2fr4
400gbase-ar8
400gbase-cr8
400gbase-dr4
400gbase-fr4
400gbase-lr8
400gbase-sr8
400gbase-xdr4
40gbase-ar4
40gbase-cr4
40gbase-er4
40gbase-lr4
40gbase-lrl4
40gbase-plr4
40gbase-plrl4
40gbase-psm4
40gbase-sr4
40gbase-srbd
40gbase-univ
40gbase-xsr4
50gbase-cr2
50gbase-cr2n
50gbase-cr2s

Some of these "transceivers" are copper based DACs, AOC or standalone modules, regardless of copper or optical.
 
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kpfleming

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Sorry, I mistyped: the ICX7250-24P (not 7150-24P) has 8 SFP+ ports. Only 4 four can be used with DACs in most circumstances, this is documented in the user's manual and is clearly stated that the limitation is due to the presence (or absence) of retimers.

The SFP+ plugs on the ends of DACs are just electrical connections, they are purely passive and do not contain any active components. They are not transceivers, they are just wiring.
 
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kpfleming

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Since I was partially the reason for that, I'll try to provide a direct answer to your question here!

You've got a TP-Link T1700G-28TQ with 4 SFP+ slots. You also have a PC with a Connect-X 3 card with two SFP+ slots. You want to establish a 10Gbit link between them. They are not located in the same room, so DACs and AOCs are not options. You will need transceivers, in-wall cable, and patch cables.

Your options are:

* Copper - Cat6 (or better) 4-pair UTP cable in the wall, terminated in compatible RJ-45 jacks. Cat6 (or better) 4-pair UTP patch cables. 10Gbase-T transceivers (example: 10G-T SFP+ Copper module).

* Fiber - OM3 (or better) multimode duplex cable in the wall, terminated in duplex LC jacks. OM3 (or better) multimode duplex patch cables with duplex LC connectors. 10Gbase-SR transceivers (example: 10Gb/s SFP+ SR | SFP-10G-SR | J9150A | SFP+ 10GBase-SR - 10Gtek).

* Fiber - Singlemode duplex cable in the wall, terminated in duplex LC jacks. Singlemode duplex patch cables with duplex LC connectors. 10Gbase-LR transceivers (example: Cisco SFP+ LR SFP-10G-LR 10GBase-LR SFP+ Transceiver - 10Gtek).

* Fiber - Singlemode simplex cable in the wall, terminated in LC jacks. Singlemode simplex patch cables with simplex LC connectors. 10Gbase-LR BiDi transceivers (example: BiDi SFP+ 10GBase-LR Tx1270/Rx1330nm 10KM).

You could mix options 3 and 4, using duplex cable in the wall but only simplex patch cables and BiDi transceivers; this would leave one of the fibers in the wall 'dark' for future use.

The least expensive option will be option 2, unless you already have Cat6 (or better) UTP cable in the wall.

The singlemode options may be problematic if the in-wall cable run is relatively short (less than 50-100 feet), as the lasers in those transceivers are designed for much longer distances.
 

DavidWJohnston

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Sep 30, 2020
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Oh boy... Lots of good info here. I can see there is some confusion - At the risk of making it worse, I'd like to try and resolve it, for the OP's benefit at least:

The "C" in "DAC" means "Copper". (Direct Attached Copper) - It has an SFP+ connector at both ends. There is nothing optical in it. The whole thing is called "twinax"; 2 wires with shielding. Those wires are electrically connected to contacts on the SFP+. They are not a transceiver, but use the shell of a transceiver to physically fit inside the SFP+ port. The lack of optical makes them useful for short runs, as they are cheap. It's copper the whole way through.

DAC:
1679064539163.png

When the OP said "I want optical" I suspect he may actually mean "I want to make use of the SFP+ ports on my equipment" - Not necessarily that he wants literal fiber optic. (This could be wrong)

There is something else called an "AOC" or "Active Optical Cable". They have bona-fide optical transceivers at each end (not just a shell like a DAC), but they are permanently connected, non-removable. The "wire" portion isn't a wire, nor is it copper - It's a glass fiber optic with light blasting through it. These work at longer distances.

A transceiver is an optical/electrical interface inside an SFP+ enclosure. Like the end of an AOC, but the fiber can be removed. You plug a fiber optic cable between these, with LC connectors, for example. The word "transceiver" means " bi-directional conversion of signal regimes", implying an electrical/optical interface. In radio, a transceiver is an RF/electrical interface - A transmitter and receiver in the same box.

Transceiver:
1679065046772.png

Some people refer to "AOCs" as a type of DAC - People say this, but it's not strictly correct because the C in DAC is "Copper". But people still say it, or they say "Active DAC", etc. It's a bit like saying "Koala Bears" or something - They're not really bears but the name is in common parlance.

Some people may also call the connector at the end of a purely-copper DAC a "transceiver" - Again, not strictly correct, there is no electrical/optical interface, it's just 2 wires soldered to a tiny board. But it's in common parlance to call them built-in transceivers.

Anyway, I hope this helps more than it causes additional confusion.
 

Railgun

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Jul 28, 2018
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Some people may also call the connector at the end of a purely-copper DAC a "transceiver" - Again, not strictly correct, there is no electrical/optical interface, it's just 2 wires soldered to a tiny board. But it's in common parlance to call them built-in transceivers.
As I had said, for the purposes of this discussion.

Know your audience.
 

klui

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Feb 3, 2019
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Active DACs, as in active direct attached copper cables, are a thing. I used one to test out a 400G switch last year.
 
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TonyArrr

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Straylia
The singlemode options may be problematic if the in-wall cable run is relatively short (less than 50-100 feet), as the lasers in those transceivers are designed for much longer distances.
I’m currently doing more or less option 3, with the plan that I can ”convert” to option 4 later with bidis if I need to.

The fibre is running though the roof space before dropping down the walls (which is gonna be real fun, 10cm between roof and slab), which I think almost gets me my distance to be OK for the single mode, but it was my understanding that there are devices you can run the fibre through to make single mode happier with the shorter distance?

Anyone know what I’m talking about (since more info could be beneficial to both myself and the OP), or have I merged some random bits of knowledge to make up something fake in my head (a la chatGPT;))
 

TonyArrr

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Straylia

klui

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Feb 3, 2019
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Generally a non-issue, see slide 78 here. Only an issue for 80km and maybe some 40km optics.
Looks like from that presentation LR transceivers are 0.5dBm from receiver blindness. That doesn't seem like a whole lot of headroom: ~10% according to dBm to watts conversion calculator. Granted, that's the low end of threshold to high end of transmit power.

From a practical point of view, CWDM4 LR4Ls are probably the best way to make use of SM fiber on short runs if you want 100G with duplex LC connectors. Or get OM4/OM5.

EDIT: I forgot I viewed this a long time ago... for the context from Mr. Steenbergen himself
The case he gave was 6" drop and 80kM optics.
 
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