
Everything You Always Wanted to Know About Optical Networking [pdf] - andreasley
https://www.nanog.org/sites/default/files/2_Steenbergen_Tutorial_New_And_v2.pdf
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dvno42
I just did my first municipal ISP design not too long ago and this document
was an excellent introductory guide to the topic and understanding optics in
general. The documentation for DWDM muxs (Ex: BTI and MRV) were also
invaluable in learning how to apply the concepts outlined in the above
document. This definitely expanded my horizons in the service provider
networking field. Ex:
[http://www.juniper.net/support/downloads/?p=bti7200#docs](http://www.juniper.net/support/downloads/?p=bti7200#docs)

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madsushi
YouTube link for the most-recent talk:
[https://www.youtube.com/watch?v=__wn9zXFiy8](https://www.youtube.com/watch?v=__wn9zXFiy8)

I've seen a couple versions of RAS' talk and learn something new every time.

~~~
spydum
yup, smart dude, learned plenty as a self-taught network grunt subscribed to
nanog in the 2000-era and hanging out on irc, listening to guys like rs

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femto
Neat to see that optical is the new RF, in that it is using coherent
modulation techniques that were once restricted to radio. In a similar vein,
RF is also the new baseband (like audio and video before), in that the lower
ends of RF (VHF and below) are transitioning to direct sampling at a
reasonable cost.

The takeaway for me is that there are opportunities for people with experience
in radio modulation and DSP to move into the optical game.

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sneakertack
Is slide 6 (Fiber Works by "Total Internal Reflection") wrong? I thought that
total internal reflection (TIR) happened when trying to cross from a higher
refractive index (RI) medium to a lower one - not the other way around as
depicted by the core-cladding boundary. Furthermore if the cladding has a
higher RI, then the rays should become steeper upon transiting, not flatter
like shown in the diagram.

I always thought fibers were single material (i.e. just the core) because the
surrounding air (lower RI) lets TIR happen. It certainly seems to be the case
in the next slide (Demonstration Using a Laser Pointer), TIR on Wikipedia [1],
and pictures of fiber optic lamps [2].

[1]
[https://en.wikipedia.org/wiki/Total_internal_reflection](https://en.wikipedia.org/wiki/Total_internal_reflection)
[2]
[https://duckduckgo.com/?q=fiber+optic+lamp&t=canonical&iax=1...](https://duckduckgo.com/?q=fiber+optic+lamp&t=canonical&iax=1&ia=images)

Okay after reading a bit more [3] I'm pretty sure it's wrong, and the cladding
RI's must be lower. So my follow up question is... what's the point of the
cladding? Why not just rely on the surrounding air?

[3]
[https://en.wikipedia.org/wiki/Cladding_(fiber_optics)](https://en.wikipedia.org/wiki/Cladding_\(fiber_optics\))

~~~
kurthr
Yes, you're right the cladding is lower index, and it is a controlled index!
It (along with other layers) protects the inner core. Most data transport
fiber is single mode, which requires very tight control of the ~8um 'diameter'
of the high index core, but allows for lower loss/km and you don't get mixing
of the different modes (think of them as different reflective angles for
simplicity). If air was used then any scratch or dirt contacting the core
would couple light out.

In fact most multi-mode is graded index and it's much easier to get light into
(8x larger core) without a specialized coupler. Note that even single mode
allows DWDM- many different high-bandwidth wavelengths, but only 40nm spacing
on 1560nm IR. The core, cladding, and outer protective layers are extruded and
pulled to extremely precise dimensions, dispersions, and densities into multi-
km rolls.

The games that are played to equalize loss and delay among the wavelengths
over a range of power and temperature is crazy... and that's ignoring the EDFA
optically pumped fiber amplifiers, which let under sea cables work. Amazing
tech!

~~~
aidenn0
Has graded-index multimode caught on now? I last learned about fiber in the
90's when it was still something new.

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sengork
Thanks this is the first time I have come across
[https://en.wikipedia.org/wiki/Yokogawa_Electric](https://en.wikipedia.org/wiki/Yokogawa_Electric)

Also it's refreshing to see that they mention "seeing" IR light from a remote
control via your mobile phone's camera. This trick has been around for years
(thanks to cameras tendency to colour shift) however it is rarely known about.
The author is indeed a practitioner.

~~~
wyager
Modern phones don't see IR very well on account of improved filters. My iPhone
can't see remotes at all. An IR source needs to be much more powerful to show
up.

Back in the day I took the IR filter out of my digital camera and got some
cool (dismal 3.2MP resolution) shots.

~~~
photojosh
The rear camera has a very strong IR blocking filter. But the front camera
doesn't. (We have a product that uses IR LEDs as a flash, and I use my front-
facing camera to verify they're working.)

~~~
thomasjudge
Thanks for this! Works on iphone 6

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paco3346
As someone who used to work with optical equipment this is really awesome. My
team was responsible for the SDN layer that sat on top of the nodes and
configured them so we were taught enough to be dangerous but I always wondered
what was really going on under the hood.

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ksec
Why are we still stuck with Copper RJ45 Ethernet twisted Cable @ 1Gbps for
Local Networking / last Mile? While there are up coming NBase-T which offer up
to 2.5/5Gbps Ethernet, they are expensive and no where near as cheap as 1Gbps
Port. Not to mention most Vendor will likely put out 2.5 Gbps instead of 5Gbps
due to cost reason.

Why is there no common, simple, cheap Fibre Cable and Port to replace our age
old RJ45 and Copper Cable.

P.S - I actually rather have NBase-T, but at the moment no one is offering it.
At least not at the price bracket most would pay for it.

~~~
aidenn0
Cat-6 can take 10Gbps over ~50m runs, and the cards are under $100 now

~~~
sigstoat
can you point out such a card? the closest i've seen is
[https://www.newegg.com/Product/Product.aspx?Item=9SIAD5G5M36...](https://www.newegg.com/Product/Product.aspx?Item=9SIAD5G5M36425)

~~~
aidenn0
You can usually find refurbished ones, e.g.:
[https://www.newegg.com/Product/Product.aspx?Item=9SIA9AX5D88...](https://www.newegg.com/Product/Product.aspx?Item=9SIA9AX5D88720)

And B&H has a new card on preorder for just barely under $100:
[https://www.bhphotovideo.com/c/product/1344847-REG/asus_90ig...](https://www.bhphotovideo.com/c/product/1344847-REG/asus_90ig0440_ma0r00_xg_c100c_10g_network.html)

~~~
sigstoat
thanks!

it looks like asus has also introduced lowish-priced switch with some 10G
ports, too. [https://www.amazon.com/XG-U2008-Unmanaged-2-Port-8-Port-
Giga...](https://www.amazon.com/XG-U2008-Unmanaged-2-Port-8-Port-
Gigabit/dp/B01LZMM7ZO/)

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xemdetia
This feels like a great resource to me, it's 125 slides chock full of stuff.

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bluedino
>> Light, like sound, follows the inverse square law. • The signal is
inversely proportional to the distance squared. • A signal travels distance X
and loses half of its intensity.

I thought light (at least photons) don't lose intensity? Is this through the
medium that fiber optics are made of?

~~~
tadfisher
Yes, no material is 100% reflective, and some of those photons will either be
absorbed by the material or reflected in the wrong direction.

It's explained two pages prior on Page 14.

~~~
elihu
I think the slide on page 16 is wrong; the inverse square law comes into play
when light is unconstrained and spreads out in all directions. Losses that
come from impurities in the glass and so forth attenuate differently.

For instance, if you're looking at light intensity from a lightbulb, every
time you double the distance you get 1/4th the intensity, or that comes out to
about a 6 decibel loss.

If you're shining a light through an optical cable, it might lose half it's
intensity every time it goes, say, 10km (I don't know what the number is for
proper high-quality single-mode fiber, so we'll just go with 10km). So, your
loss is about 3 decibels per 10km.

Over short distances, the small fixed loss of the cable isn't significant, but
over very long distances, the 3 decibels per 10 kilometer loss adds up a lot
faster than 6 decibels every time you double the distance.

~~~
femto
I'd say it's unclear rather than wrong, and what you say is perfectly correct.

Decibels are useful when dealing with exponential decay, meaning that the
output of a process is always proportional to its input. An inverse square law
is an example of this more general case, so I think the author is just holding
it up as an example, rather than saying it applies to fibres. Other examples
are inverse (which holds for fibres as you point out), or any other choice of
exponent.

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danellis
More like physics than networking. I was hoping for more about what goes on
between light and IP, but all I learned is that SONET/SDH is considered old
school now.

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devnull42
This is a fantastic guide. Thanks for putting it up!

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alexpetralia
Super practical and concise guide.

