Are sharks eating your internet?!

[webecedarian]

This was a little news item on television.

http://www.usatoday.com/story/news/n...vlar/14099761/

http://www.forbes.com/sites/amitchow...dersea-cables/

http://www.slate.com/blogs/future_te...les_video.html

[EmailHosting]

I think it would be tough to locate where the shark had eaten the cable considering that they can't even locate a massive Malaysian airlines flight if it had really crashed into the ocean.

I guess they will need to build a sharp wired fence around the cable. Ha Ha!

[n5bb]

They sure have some non-technical writers for those websites! If those cables are truly only carrying fiber optic communication cables, I'm sure the sharks aren't attracted to the "electromagnetic fields". That term refers to everything from static electricity to mains power line 50/60 Hz frequencies to audio frequencies we can hear with our ears to radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma ray radiation. Although these all obey Maxwell's Laws, the different frequencies interact with matter and propagate in quite different manners. For example, just because someone located a kilometer from you is listening to music on their earphones (which carry and radiate electromagnetic fields) doesn't make it possible for you to listen in to their music. However, if they were transmitting on an antenna as long as your arm on certain RF frequencies, it would be moderately easy to listen to them.

Sharks are sensitive to very low frequency electric fields. You would not expect fiber optic lines (which carry energy in infrared wavelengths not too far from visible red light) to attract sharks who can only sense frequencies many billions of times lower in frequency, unless metallic wires or metallic shielding were also embedded in the cable. I think they are just curious, and the smell of the cables or mechanical vibrations (sound) conducting down the plastic cable outer protective layers also might be attracting them. Sharks are very sensitive to smell and vibration.

With regard to locating a break in a fiber optic cable -- this is pretty easy. You obviously have access to each end of the fiber and can send test signals into the fiber from either end. There are two main types of breaks which can occur, and the fault is located using an OTDR (Optical Time Domain Reflectometer).

• A specular reflection (similar to the reflection of a shiny metallic object in your car headlights at night) is located by sending a very short pulse of light down the cable and looking for a reflection from the break. A very accurate timing circuit is used to determine the time to the reflection, and since the speed of light propagation in the glass fiber is known precisely it's easy to calculate the distance to the fault rather accurately.
• Attenuation (which is what you would expect if the glass fiber was sharply bent) can produce no reflection. These breaks are located by sending a high energy light pulse into the fiber and measuring the measuring the backscatter from impurities in the glass versus time. If the backscatter signal disappears after a certain time, that can be used as before to calculate the distance to the break or bend.

Bill

[sokita]

You think, the image which is a photoshop?

[chuckster]

the number one reason Fastmail is often down under.