Repair Crews Reach Vicinity of Damaged Cables In Mediterranean 145
GWMAW writes "A robotic submarine searched beneath the Mediterranean on Sunday for damaged communications cables, two days after Web and telephone access was knocked out for much of the Middle East.
Telecommunication providers from Cairo to Dubai continued Sunday to scramble to reroute voice and data traffic through potentially costly detours in Asia and North America after the lines running under the Mediterranean Sea were damaged Friday." According to the article, "Once found, the cable ends will be pulled to the surface and repaired on deck — a process that could take several days."
Re:How do they do it? (Score:5, Informative)
How do they repair the cables? Especially with glass fibre I wouldn't know what to do.
My assumption would be that there are points built into the cable where you can exchange out bad segments for new segments.
Re:How do they do it? (Score:4, Informative)
http://www.laser2000.co.uk/fusion_splicers.php?area=262
Re:How do they do it? (Score:1, Informative)
How do they repair the cables? Especially with glass fibre I wouldn't know what to do.
http://www.francetelecom.com/sirius/dossiers_anim/cables_sous_marins/index_en.html
Re:How do they do it? (Score:4, Informative)
fiber splicers - its mostly done in the field because in house we have handy-dandy prespliced fiber cables of different lengths. If you see (fill in local ILEC) out repairing a cut cable, chances are they might be splicing.
Re:How do they do it? (Score:5, Informative)
Optical Time Domain Reflectometer. You just ping the broken end and get a distance measurement.
Re:How do they do it? (Score:5, Informative)
With a device known as an Optical Time Domain Reflectometer [wikipedia.org]. Supposedly they can not only detect cable length, breaks, but even the location of splices.
Re:How do they do it? (Score:5, Informative)
The actual fiber repair is done pretty much as it would be done for terrestrial cables. Either a fusion splice, usually by re-cleaving the ends for a clean surface and vibrating the ends ultrasonically to heat by friction and weld them together, or a very small splicing kit that holds the ends in near-perfect alignment, usually filled with a gel of identical optical properties to reduce the loss and refraction. Since space is an issue, I suspect fusion splices are the only acceptable option.
The biggest problem is both accomodating the repairs to the fiber jackets, and then re-sealing the cable. I wouldn't be suprised that there are fairly standard splice boxes that solve this.
Replacing segments doesn't seem like a good option. Any useful segment should measure miles in length, which is pretty expensive. Even replacing a segment and hauling the old one in for repair sounds like more trouble than it's worth. Of course, repairs on the open sea sound like fun to me. I had enough trouble sitting at a little worktable in a dim cable room with equipment balanced here and there, and testing going on constantly. A nice 20-30 foot sea would make me want to apply at the local McDonald's. Life is too short.
But nice work if you can do it.
Re:How do they do it? (Score:5, Informative)
Luckily you can have both in one :)
http://duckproducts.com/products/detail.asp?catid=1&subid=1&plid=3 [duckproducts.com]
Re:How do they do it? (Score:5, Informative)
How do they repair the cables? Especially with glass fibre I wouldn't know what to do.
They drag the cable up and cut it (assuming it is not already in two pieces). They strip back the armor and sheath on both pieces. They then splice in a new piece of cable using a fusion splicer, which basically lines up each individual fiber (quite a time-consuming process to clean and prep each piece) and then the fusion splicer essentially melts the fiber strand back together. They put heat-shrink and something like a splint to keep it from bending over the spliced area and then fit each splice into a tray. The trays are then mounted into a splice case. Submarine cables are much more difficult because it has to be well sealed and able to withstand significant pressure.
The faults are located using an OTDR (Optical Time Delay Reflectometry), which basically sends light down the fiber and measures the reflections. As we know the speed of light we can accurately measure the distance to a break, imperfections, etc of the cable and splices.
Re:How do they do it? (Score:3, Informative)
They cut the cable in half, and put a new piece in it. They can locate the exact point of failure using an OTDR, as already mentioned in other comments by now.
In one such big under-sea cable, there could be hundreds of individual fibers inside. (It doesn't cost alot more to put another fibre in the big cable, and you get alot more bandwidth to sell).
For each fiber inside the cable they "weld" it to the new piece they are putting between. (I'm sorry, I don't have the correct translation for the word in English). But really, they put the fiber in a machine, together with the fiber of the new cable they are putting in between, and they hit a button: "weld". It creates an arc through the point where the fiber needs to be welded together. After the arcing you heat that spot so the atomic structure can repair a little.
Repeat 500 times and put some extra mechanical protection around to protect your welding, and you're done.
There exists equipment that can do multiple fibers at once, so basically the engineer who's doing it just needs to place both ends of the fibers in the machine, hit the button, remove fiber and repeat for a day or 2.
Re:How do they do it? (Score:3, Informative)
Actually, you can. You use a device called a Time Domain Reflectometer [wikipedia.org], which sends a pulse down the line and times how long it takes a reflection to come back.
2 * Distance = Speed of light * Round trip time
To find the location of the fault to within ten feet you need a timer with about a 20 nanosecond resolution, which equates to a 50 MHz counter -- not too difficult.
Gilligan Saved the Cable! (Score:3, Informative)
Re:Satellites FTW? (Score:3, Informative)
Geosychronous orbit has too much time latency, and LEO takes more satellites to cover the same area. It'd be cheeper to just lay more cable, but corporations tend to push for raw efficiency rather than redundancy. It's going to take governments using their buying power to encourage redundant routes to get us back to where DARPA was in the '80s.
Re: Slack (Score:5, Informative)
There was a terrific article written for Wired by Neal Stephenson (yes, that Neal Stephenson!) called Mother Earth Mother Board [wired.com] all about the laying of the longest underwater telephony cable in history. He goes into a lot of details as to how the cable is laid, what happens to the cable when it reaches shore, what is the cable made of, how does it work, etc.
Here's an excerpt where he explains how slack affects the process:
Re:How do they do it? (Score:5, Informative)
Actually, there are repeaters in line, albeit I don't remember the distances. There's a big copper conductor in the jacket (just one, the ground is the ocean itself) sending a couple hundred volts through it.
Re:How do they do it? (Score:2, Informative)
Ok, I'll bite.
Optical fiber cables are connected by first identifying each strand in the bundle, and the other cut end of that same strand. Matching strands are taken, one set at a time, into a fusion splicing machine. The fusion splicing machine aligns the strands, then heats the ends so the glass melts together.
Older splicing machines required the person operating the machine to visually ensure the strands were aligned, and the heating was automatic. New machines perform computer-guided alignment and automatic heating. These machines commonly cost about as much as a nice new car (around $30-50 thousand U.S. dollars, IIRC) and require specialized training and supplies for regular, telephone-pole mounted cables. Undersea cables probably have extra special costs.
In any case, a bundle with hundreds of strands takes days to repair. It can take several hours to splice a broken 36 strand cable.
You can only get so many machines close enough to the broken cable, so the work does not allow for, say, 50 splicers to all work on it at once.
Of course, I'm glossing over all the work it takes to pull a cable off the sea floor, get it on a ship, and then put it back. Someone else can gather karma for that info ;)
Re:How do they do it? (Score:4, Informative)
how do you propose to power it?
I'm not saying power couldn't be supplied, but I don't think it'd be cost effective, and you'd need to run a whole new set of lines.
The same way the repeaters are already powered - the are power leads bundled with the fiber cable. In a full cut, they would have to repair the copper power leads anyway.
Re:How do they do it? (Score:4, Informative)
Fusion splices are the only acceptable option because you can't afford to have a 0.1 dB splice on a long fiber. Too much loss will upset your whole link budget and you will not get an acceptable SNR at the far end.
BTW, I have never read how a fusion splicer works, but all the ones I have used align the fiber and look like they send a current between two metal contacts for ~0.2 seconds that fuse the fiber. I'm pretty sure ultrasound isn't used. When you are trying to align two fibers exactly, vibrating them doesn't sound like a good idea.
Re:How do they do it? (Score:1, Informative)
This is not far from wrong actually. The superglue is optically identical in refraction index to the cable and the duct tape is a thermal shrink wrap designed to handle long term exposure to salt water. But that's essentially it. It take a long time to fix all those broken fibers.