Telecomunication Fiber Optic Cable

Hi everybody,

in our Neighbourhood a Tele-Com Company is installing Telecomunication Fiber Optic Cable with a 1" outside Diameter, i would asume that the bundle of Optic Fiber is about 1cm2 , my question is, how much Data could be sent trough the Cable in Gb/sec.?

Thanks for any information.

Depends how many strands, and how many are lit?

When we were installing F/O in our location, the cable came in 6, 12, or 24 fibres. Then there’s single-mode or multi? For longer distance telecoms (and now even locally for 1GB ethernet) single mode is the choice. Single mode is usually about 10/125 and multi 62.5/125, which is the diameters of the inner/outer glass cores in micrometers, IIRC. Multimode is easier to work with and more forgiving, but for ethernet has ranges on the order of 1000m, vs. ranges in kilometers for single mode. (60km, IIRC?) The rest is armouring and bend-proofing outer jacket, a center core metal wire to prevent stretch damage, and gel fill to insulate the cable. I was told bears found the gel fill very tasty.

The rule of thumb was that by about 2005, fiber was much cheaper than labour (used to be other way) so spend the extra 20% and put as much fiber as you can while you have the guys pulling it and digging trenches; you can always hook it up later a lot cheaper than you can lay a second cable.

Speed depends on how much you want to spend on electronics and how far apart you put the repeater elements. The light source sprays out in a fan - so some light goes straight, some zigzags, bouncing back and forth off the sides of the fiber and taking longer to get where its going. As a result, what starts as a nice square wave mushes into a fuzzy curve shape a long distance away.

Then there’s multi-spectrum technology, which when you strip of the science gobbledygook means use several different-coloured lasers on the same fibre to make multiple channels.

And finally, what you could theoretically push down the pipe and what is cost effective in a business environment are 2 different things. Odds are they are using each fiber for T3, which IIRC is about 150Mbps (bits). The off-the-shelf equipment to do that is probably quite cheap by now. If/when the new stuff becomes cheap, and demand warrants, upgrade. Same like you can buy 10Gb copper ethernet, but unless you are running the Google data center, how badly do you need that?

Not sure what the theoretical max throughput is now on fiber - the actual number probably depends on the distance you want to cover.

T1/T3 instead of ethernet because if you have to carry telephone circuits too, it makes more sense to use the established telecom standards. Possibly nowadays they may dedicate a strand for data. Don’t forget for 2-way, you need one strand each way. Unlike electric circuits, there’s no need for ground, obviously.

Of course, that was about 3 or 4 years ago. The telecom market may be 100% different today.

Thanks MD200,

very good explanation of many things i did not have a clue about!

The outside diameter of the bundle is somewhat unrelated to the number of fibers insde, since most of the thickness is to protect the somewhat fragile glass fibers. An outdoor-rated bundle from 2 to 48 fibers will generally have the same diameter.

Beyond that, the cables do get fatter. The highest fiber count I’ve seen in a single jacket is 1536 fibers.

How much data travels over a single fiber depends on what needs to be sent and how far it is going - there’s a trade-off between number of fibers and the cost for fancy equipment on each end. At the low end, you can send a single T1 (1.5Mbit/sec, slower than original Ethernet) over a pair of fibers. At the high end, it is pretty much unlimited for our purposes - hundreds of gigabits/sec can be easily done today).

For cables where you are installing the connectors yourself, single mode is not much harder than multimode - one more polishing step in most systems. The “single mode is hard to deal with” comes from long-distance runs being fusion spliced (the glass ends are melted together) rather than by using connectors, since fusion splices degrade the signal a lot less.

Depending on the type of data being sent, you can go amazingly long distances without repeaters to regenerate the signal with single mode fiber. 10 years ago, we were getting from New York to Boston (300+ KM) with no repeaters.

That stuff is called “icky pic” for a very good reason. It is essentially silicone bathtub caulk that never hardens. Animals just like to chew on cables. Squirrels are a particular problem.

Most underground fiber is placed in conduits rather than directly buried, so it would always be possible to pull it out and put in a larger one - most fiber uses 2 redundant paths to reduce the impact of backhoe incidents.

However, some places charge you by the number of fiber strands you pull, regardless of whether you’re using them or not. “Carrier hotels” like 60 Hudson behave that way.

Coarse or dense wave-division multiplexing technology (CWDM and DWDM).

T3 (DS3) is about 45Mbit/sec. OC-3 is 155Mbit/sec. Depending on the telco involved, they may or may not run fiber to deliver T1 (1.5Mbit/sec) circuits. Inexpensive equipment to deliver 4 T1’s on a pair of fibers (QFLC) has been around for over 20 years. But, since those same 4 T1’s could be delivered on 4 traditional paired copper phone lines, the telco may not want to run fiber. I suspect it is driven more by how good they want to look to regulators (“hey, we deployed over 10,000 strand-miles of new fiber last year!”).

Actually, after years of trying to ignore Ethernet, telcos are now offering Ethernet circuits directly to customers (Ethernet hand-off vs. something like an OC-12). Because Ethernet doesn’t fit conveniently in the hierarchy of traditional telecom speeds, this has forced the deployment of new equipment like the Flashwave.

A Gigabit Ethernet link (1000Mbit/sec) currently generally costs me about 3x the costo of a T3 link (45Mbit/sec) so it is a worthwhile upgrade and most of my links have been upgraded. The few remaining ones are between places where there isn’t enough carrier competition to drive prices down.

Using CWDM or DWDM, you can put both the “up” and “down” signals on a single fiber. That costs more than using 2 fibers, so again it depends on the distance-vs-equipment cost tradeoff. And you’ll probably want a backup path regardless of whether you are using 1 or 2 fibers, to avoid those pesky backhoes.

Let me add my $0.02…

Cable operators now use 10 Gb/s/wavelength for long haul. 40 wavelengths per fiber is routine. So, a single fiber can now support 400 Gb/s. Very few links currently use more than 10 active wavelengths with two or three being common.

The number of fibers in a single cable ranges from 2 to 240 fibers. (I’ve never seen a cable with 1536 fiber, but it would be fun to!) 24 is fairly common for long haul applications. Edge and access networks more often use 4 to 12 fibers in a cable.

A few years ago I worked with a guy who got a kick out of holding a single, active fiber between his thumb and forefinger. It gave him a great sense of power knowing how many bits per second were flowing between this fingers. I thought he was a bit odd.

I think it depends on where your market is located and the industry (cable TV vs. telco). Around here, when we order a T1 to somebody’s house the telco brings anything from a 24 to 96 strand fiber, though not all of those are spliced all the way through to the central office. Looking at the engineering drawings for the telco fiber run to my house, there are 24 strands from my house to the street (6 spliced), 72 along the street to to the feeder (12 spliced), 72 in the feeder to the trunk (24 spliced) and 144 in the trunk to the CO.

The next time I’m at one of our facilities I’ll take a picture of a 768- or 1536-strand cable. It is pretty boring on the outside - just a big black tube with some tiny white print that tells the brand, manufacture date, and number of fibers.

How do you keep track of which fiber is which? Are the individual strands color-coded like copper cables (blue, orange, green, brown, etc) and then wrapped into color-coded bundles, or is it just one mass of fibers and you get to play hide and seek?

And that can’t be much fun - it’s not like copper where you can put a toner on a pair at one end of a cable and then wave a tracer around at the presumed other end to find which of 60 otherwise identical cables is the one you need.

It depends on the brand of the cable (for outdoor cables). First is groups of 12, which are color-coded and/or held together in a flat “ribbon”. On ribbons, the outer covering can just have a number printed on it and that’s it. For loose fibers and ribbon cables with a large number of ribbons, these groups can have a thin color-coded indicator (string or tape) wrapped around them, and/or placed in a sub-tube within the outer fiber jacket. 3 levels of 12 gets you to 1728, which is more than enough.

Fiber splices tend to be a lot less ad-hoc than copper ones. In an enclosure where splicing is done, there are trays which hold each bundle of 12 fibers securely. For fibers that pass through without splicing (whether they are live or available for future use) they’re coiled (mostly neatly) out of the way.

Most telcos leave a number of coils of slack outside the splicing enclosure, so the whole thing can be taken down (from the pole) or pulled out (of the manhole) and into the truck for splicing. These trucks are dedicated to splicing work.