When being abroad or accessing information stored on a server on another continent, the data traverses submarine cables, sometimes for more than 10.000 km in one hop before resurfacing at the other end. Quite a piece of technology I knew but little about so far. Recently, however, a comment to a post contained an interesting link to Greg's cable map of deployed submarine cables that contains interesting information about each cable and links to further details, many of them on Wikipedia. This entry contains general information about submarine cables and here, here and here, as an example, some information can be found on a particular cable (TAT-14) that is currently used in the Atlantic.
Here are some facts which I found interesting:
Capacity: The system capacity of the cable is given as 1.87 TBit/s or half in each direction by the third link above on the TAT-14 website. The two Wikipedia articles linked above give some more details on how the capacity is calculated but the descriptions do not match the 1.87 Tbit/s. The next cable generation seems to be close to be brought into operation, however, with the WASACE cable, foreseen to enter operation in 2014 having a capacity on Greg's cable map of 40 TBit/s, due to the use of 100 Gbit/s per wavelength instead of the current 10 MBit/s.
Signal regeneration: The German Wikipedia entry states that there is a repeater every 50-70 km but does not give a source from which this information was obtained. The English entry mentions the use of erbium-doped fiber amplifiers (EDFA) as repeater / amplification technology, also without a reference, that amplifies the light signal directly to light again without conversion into an electrical signal first. EDFA is also mentioned in the general Wikipedia article on optical data transmission (see section on "optical telephone cables") as the amplification technology for intercontinental cables.
Below ground: If possible, the cable is laid one meter deep into the sea bed to protect it from anchors and fishing nets that seem to frequently plague cables in areas where they are not well protected.
Lifespan: Cables laid at the end of the 1980's (i.e. before GSM was launched in 1992 to give a reference) such as TAT-8 (the first optical cable through the Atlantic!) and PTAT-1 were operated until 2002 and 2004 respectively. In less than 15 years, the cable's capacity of 20 GBit/s, which equals 40.000 telephone circuits according to the Wikipedia entry became only a fraction of the capacity offered by new cables coming online in those years such as the TAT-14 with a used system capacity of 1.87 TBit/s. This is two orders of magnitude greater. In other words, the 10-15 year telecoms cycle found in mobile networks (GSM - UTMS - LTE) applied to this field of telecommunication as well.
I agree this is a fascinating subject. There a few videos on youtube that show how the cables are laid. This one from an exhibition shows the optical repeaters from NEC http://www.youtube.com/watch?feature=fvwp&NR=1&v=tXwPuWlX4O8
Posted by: Mark | January 16, 2012 at 07:23 PM