Looking for: Introduction to Fibre Optics for the Copper Cable user

Rand__

Well-Known Member
Mar 6, 2014
6,390
1,617
113
I am trying to wrap my head around the many options and components needed to run fibre optic cables between two buildings (max length some 30m).

I primarily used Copper & DACs before and have looked into fibre optics a bit wrt to different connectors.

At this point I am lost in many ways,
eg

-how to map nr of fibre strands in a cable to the SR/LR mapping of transceivers (ie do I need 4 strands for a SR4 cable? can I add 3 transceivers to a 12 fibre cable);
-also I see a lot of fibre cables in large lengths with preconfigured connectors but am not sure if I need to get those? Or is there free length cable that can be connected to a fibre drop (by someone with appropriate tools)
- why would I need a splice box over a simple drop - is that if I have more fibre strands then needed for a single drop?
-Is it better to get 4 premade 30m cables and drop them in the ground (inside a conduit) or get 1 cable with 4 times the strands and use a splice box (and pay sb to connect cable to the box)?
-What cable to get - will OM4 suffice for <50M for 200Gbit or more (in 10 years) ?


So question upon questions - is there anything like a definitive guide anywhere? Have not found anything, but maybe all the wrong keywords...

Edit: Lets keep on multimode fibre here, dont think single mode is needed for length
 
Last edited:

AndreiL

New Member
Jun 30, 2019
23
9
3
-how to map nr of fibre strands in a cable to the SR/LR mapping of transceivers (ie do I need 4 strands for a SR4 cable? can I add 3 transceivers to a 12 fibre cable);
You can run as many strands as you need to, terminate them on patch panels and label each tx/rx pair. You can run individual strands or get a parallel/bunched trunk cables with as many strands as you need. If you only need a few tx/rx pairs, I'd run LC pre-terminated cables and be done with it. If you need more than a few tx/rx pairs, you can run MPO/MTP pre-terminated cables to a LC breakout panel.

-also I see a lot of fibre cables in large lengths with preconfigured connectors but am not sure if I need to get those? Or is there free length cable that can be connected to a fibre drop (by someone with appropriate tools)
pre-terminated connectors are very convenient over short runs like yours, you won't have to deal with splice work which typically requires a professional with special tools. If your conduit is large enough to run pre-terminated cables, definitely go with those.

-Is it better to get 4 premade 30m cables and drop them in the ground (inside a conduit) or get 1 cable with 4 times the strands and use a splice box (and pay sb to connect cable to the box)?
If you are ever going to be dealing with LC connections than 4 individual cables will work, but if you see yourself using QSFP transceivers in the future than MPO/MTP trunk cables are more flexible since they can be broken-out to LC or used as is in QSFP modules. Avoid splice work if you can and use breakout panels.

-What cable to get - will OM4 suffice for <50M for 200Gbit or more (in 10 years) ?
OM4 is the current golden standard for 850nm transmission. You can do 25Gbps over 850nm (SR) currently, anything higher requires either single mode or MPO/MTP wiring. 200Gbps and above is currently only available over MPO/MTP wiring.

Hope this helps.
 

Rand__

Well-Known Member
Mar 6, 2014
6,390
1,617
113
Thanks for the help:)

So lets say I have SR4 transceivers which have a LC coupling
-SFP / 28
-QSFP /28
Could I use the same LC - LC cable for both and would the nr of strands within it matter? Would that be 2 strands since I have to 2 LC connectors connecting to the transceivers? Or 8 strands since thats 2 individual cables (in a pair one LC connector each) times 4 strands for SR4 ?

I have a pair of 100G transceivers (Q28-100G-SR4) which have an MPO12 connector - is the choice of connectors an arbitrary one or are there rules on speed to connectors?

If higher speeds are only available with MPO - will that be the case too in a couple of years? Would it make sense to use (either pre terminated or custom) cables with MPO exclusively then? Or are there disadvantages? Compatibility?
Or just run both? Just want to be on the safe side for the next 10-20 years - not likely to dig that up again anytime soon and now upset that i didnt do fibre 10 years ago when it was open the last time.

The conduit is not present yet, the main question will be how large the hole in the house basement will need to be (ideally as small as possible o/c)
 

AndreiL

New Member
Jun 30, 2019
23
9
3
Let's clear-up some terminology 1st to make sure we are talking about same things: SR4 means short-reach, 4 tx/rx pairs, so that would be a QSFP transceiver with MPO/MTP coupling. SFP is commonly single tx/rx pair with LC coupling. There are QSFP transceiver with LC coupling, but these are not SR and require single mode wiring.

Could I use the same LC - LC cable for both and would the nr of strands within it matter? Would that be 2 strands since I have to 2 LC connectors connecting to the transceivers? Or 8 strands since thats 2 individual cables (in a pair one LC connector each) times 4 strands for SR4 ?
Assuming you have LC coupled SFP28/QSFP28, you won't be able to use the same wiring since SFP28 SR operates at 850nm and QSFP28 LC would not be SR and will operate at 4 different wavelengths and will require single-mode wiring. LC-LC fiber cable is always a single tx/rx strand pair, so 2 strands. MPO/MTP terminated fiber is available with many strands, up-to 24 I believe. QSFP SR4 transceivers will be MPO/MTP coupled and use 12 strand MPO/MTP cable of which 8 strands are lit and 4 are dark.

I have a pair of 100G transceivers (Q28-100G-SR4) which have an MPO12 connector - is the choice of connectors an arbitrary one or are there rules on speed to connectors?
Connectors aren't specified with speed in-mind. The difference between MPO and MTP is just the quality of connector, MTP is a higher quality connector. I tend to use MTP only.

If higher speeds are only available with MPO - will that be the case too in a couple of years? Would it make sense to use (either pre terminated or custom) cables with MPO exclusively then? Or are there disadvantages? Compatibility?
It's likely that 200Gbps and beyond will be available over LC terminated fiber in the future just like 100Gbps was first available over MPO/MTP wiring, but this will almost certainly require single-mode fiber as the approach will likely be the same: 4 distinct frequencies over LC single rx/tx pair. MPO/MTP trunks are more flexible as you can break-out the strands into tx/rx pairs and use those in SFPs or use MPO/MTP as is in QSFPs. Compatibility for LC is not a concern because you are always dealing with a single tx/rx pair. MPO/MTP compatibility is more complicated since MPO/MTP cable are available with many parallel strands, i.e.: if you run a 24 strand MPO/MTP cable you'd have to use an appropriate break-out panel to make sure you end-up with 2 12 strand MPO/MTP connectors on each side for QSFP connections.

Or just run both? Just want to be on the safe side for the next 10-20 years - not likely to dig that up again anytime soon and now upset that i didnt do fibre 10 years ago when it was open the last time.
It's hard to be future proof with this technology. Single-mode fiber is probably more future-proof, but you'll be purchasing more expensive SFPs/SQFPs. As for LC vs MPO/MTP, this depends on how much fiber you will need in the future: a couple of tx/rx pairs, go with LC, more than a few go with MPO/MTP with more complex break-out design. DWDM is most flexible/future-proof, requires least fiber, but very complex to setup and run correctly, not mot mention expensive.


update: found a nice guide here: MPO design
 
Last edited:

Rand__

Well-Known Member
Mar 6, 2014
6,390
1,617
113
From what you say and what I read it looks like it might be the most sensible approach to simply dump a bunch of MTP/MPO-12 pre-terminated cables in the conduit.

I found this
1592138200943.png
in http://i.dell.com/sites/doccontent/...cuments/dell-networking-optics-spec-sheet.pdf
which indicates that a MPO 12 cable should be future proof to 400G with OM4 (or even OM3 for my short length).


Now I wonder whether I could a splitter cable to convert a (qsfp) mpo-12 cable into individidual sfp cables in case i wouldnt need qsfp...
Also what polarity would I need and is there a way to extend a fibre cable (say I have a 30m deployed but need another 10m) - is there sth like a coupling I could use?

Thanks
 

deified

New Member
Jun 11, 2020
4
0
1
FS.com has a good visual for these types of questions. Pick a trunk cable or try out a few they have different visuals for different applications. I used these as a reference for my ebay shopping. I had run LC for my 10gb before I went 40gb and wish I had MTP 12. If you run conduit that should be future proof in itself. *note that some 400gb connections use 16 fibers not 12 depending on the brand.
Untitled.png
Untitled3.png
Untitled2.png
 

AndreiL

New Member
Jun 30, 2019
23
9
3
in http://i.dell.com/sites/doccontent/...cuments/dell-networking-optics-spec-sheet.pdf
which indicates that a MPO 12 cable should be future proof to 400G with OM4 (or even OM3 for my short length).
"Should be" is the salient detail in that document; if people much smarter than me can figure out how to squeeze 100Gbps into a single 850nm frequency than, yes, MPO12 should be future proof. 100Gbps was first available with 10 parallel 10Gbps streams over MPO24, using 20 strands (10tx/10rx), but is now available with 4 parallel 25Gbps streams over MPO12.

Now I wonder whether I could a splitter cable to convert a (qsfp) mpo-12 cable into individidual sfp cables in case i wouldnt need qsfp...
Also what polarity would I need and is there a way to extend a fibre cable (say I have a 30m deployed but need another 10m) - is there sth like a coupling I could use?
This is very common and you won't have any problems splitting MPO12 into 6 LC ports for SFP connections.

Here is a link to the 3 polarity options with MPO trunking systems, of which Method B is most common and easy to understand/deploy:

The A-B-C’s of Fiber Polarity

It is also easy to extend any MPO cable with a junction, but care needs to be taken not to mess-up the polarity since these MPO junctions/couplers are available in straight-through and crossover configurations; this is similar to cat5 extension through a junction: if you extend a crossover cat5 through a straight-through junction with another crossover cat5, you will have effectively crossed-over the pins twice and nothing will work.

You also need to take a care to consider junction insertion loss, this is where light level drops by, typically, 0.3-3dB through fiber connections with high density breakout panels having IL as high as 6dB (3dB being 50% loss). This is why you want to have as much light power as you can spare by getting powerful enough QSFP/SFP modules. If you have a 30m run with 5-6 junctions, your'd want to make sure your modules are rated for at least 100m runs. I typically get 300-400m rated modules, the price difference is low enough and makes it affordable to just go with 300-400m modules all the time.
 
Last edited:
  • Like
Reactions: Aluminat

arnbju

New Member
Mar 13, 2013
23
10
3
Last edited:

AndreiL

New Member
Jun 30, 2019
23
9
3
Those are proprietary interfaces using multiple wavelengths instead of a single 850nm one. There are all kinds of vendor proprietary interfaces available. Standards-based 100GBASE-SR4/40GBASE-SR4 is defined only over the single 850nm wavelength and 4 parallel rx/tx pairs.

I guess I was a bit inaccurate above: you can do 100G/40G SR over LC MMF with proprietary interfaces.
 
Last edited: