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Fiber-Optic Link Around the Globe (FLAG) is a 28,000-kilometer-long optical fiber mostly-submarine communications cable that connects the United Kingdom, Japan, and many places in between. The cable is operated by Global Cloud Xchange.〔http://www.telecomreviewasia.com/index.php?option=com_content&view=article&id=589:global-cloud-xchange-plans-new-india-singapore-cable&catid=3:newsflash&Itemid=232〕 The system runs from the eastern coast of North America to Japan. Its Europe-Asia segment was the fourth longest cable in the world in 2008. The Europe-Asia segment was laid by Cable & Wireless Marine in the mid-1990s and was the subject of an (article ) in ''Wired'' magazine in December 1996 by Neal Stephenson.〔 ==Description== The FLAG cable system was first placed into commercial service in late 1997. FLAG offered a speed of 10 Gbit/s and uses synchronous digital hierarchy technology. It carries over 120,000 voice channels via 27,000 km of mostly undersea cable. FLAG uses erbium-doped fiber amplifiers and was jointly supplied by AT&T Submarine Systems and KDD-Submarine Cable Systems. Its design, development, installation and service conformed to ISO 9000 quality standards. FLAG provided a link between the European end of high-density transatlantic crossings and the Asian end of the transpacific crossings. FLAG includes undersea cable segments and two terrestrial crossings. The segments can be either direct point-to-point links or multipoint links which are attained through branching units. At each cable landing point, a FLAG cable station is located. The total route length exceeds 27,000 km and comprises 1,020 km of terrestrial crossings. Approximately 6,600 km of the submerged cable is buried 1 m below the sea bed. Cable burial was performed by either a submersible plough as the cable was laid or jetting the laid cable into the sea bed via remotely operated vehicles (ROVs).〔 Over several years the route evolved as new branches and feeder systems were considered and realized. FLAG includes two terrestrial crossings, one in Egypt and the other in Thailand. Each of these land crossings is totally duplicated on fully different routes. As a result, any fault within one route will cause automatic protection switching to the other route within a time period of less than 50 ms.〔 Like other global undersea networks, FLAG uses erbium-doped fibre amplifiers. EDFAs boost the optical signals instead of the optical/electrical conversion which is generally used in regenerative technology. These optical amplifiers use short, gain-specific lengths of fibre which are doped with erbium ions and spliced in-line with the transmission fibre. The signal power is amplified by pumping the erbium-doped fibre (EDF) with 1,480 nm laser light which is attached through an optical coupler. The majority of the repeater components are passive. These include EDF, fused-fibre optical couplers and optical isolators. Active components include laser pump assemblies and associated controls. The total number of components within the repeater is lesser than that of regenerative systems.〔 The FLAG terrestrial crossings do not contain repeaters for reliability reasons. The terminal stations in land crossings use optical amplifiers, high performance transmitter/receivers and forward error correction to cross the large distances without repeaters. Amplification at the terminal output provides output signal power as high as +17 dBm, and optical amplification at the receiver improves the receiver sensitivity as high as +8 dBm.〔 The route between Alexandria and Cairo is 223 km long and hence requires remote pumping in order to meet performance requirements. Remotely pumped amplifiers can be regarded as repeaters without active modules. This technology comprises short lengths of EDF spliced into the land cable. The erbium-doped sections are situated within the cable span and are pumped by 1,480 nm pump lasers which are based at the station.〔 An upgrade to the network was announced in 2006 when the acronym was expanded to "Fibre Loop Across Globe" (FLAG). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fiber-Optic Link Around the Globe」の詳細全文を読む スポンサード リンク
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