broadband strategies handbook.pdf - Khazar University

capital in the short run. Carriers opting to upgrade will install replacementfiber optic cable first on backbone routes with high volumes of traffic. Asdemand for bandwidth grows and investments can be justified, fiber progressivelyreplaces copper cables throughout the network, reaching closerto the end users.At present, most backbone networks are fiber based, even in developingeconomies, and the use of fiber in metropolitan and “middle-mile”links is rapidly increasing as well, particularly in developed countries. Asthe demand for wireless broadband grows, there is also increasing use offiber to provide backhaul from cell sites to mobile carrier switching facilities.Fiber penetration in the local access network is still very limited,even in developed countries. But the emerging trend, especially forbuilding out new housing and commercial developments, is to installfiber from the outset. Several deployment scenarios are possible for fiberoptic cable:• International connectivity—international undersea networks and internationalterrestrial networks• National backbones—national undersea networks and national overlandbackbone networks• Metropolitan rings and cellular backhaul• Subscriber access—fiber to the premises.SatelliteIn the broadband supply chain, satellites are used primarily for internationalconnectivity and some domestic backbones; they are used lessfrequently for metropolitan and local access networks. Geostationarycommunication satellites receive and transmit information from orbitalslots located 35,786 kilometers (22,282 miles) above Earth. At thisheight, the satellite appears in a fixed location when viewed from Earth;this stable location is an advantage since subscriber satellite dishes donot need to move or track the satellite.A satellite’s communication capabilities can be analogized to an invisible“boomerang” or “bent pipe,” with signals transmitted (uplinked) to the satellite,which then relays (downlinks) them back to Earth. Data are transmittedvia the communication satellite’s transponders. Satellites usually havebetween 24 and 72 transponders, with a single transponder capable of handlingup to 155 Mbit/s (megabits per second). 4 Next-generation satelliteswill offer speeds in excess of 100 Gbit/s. 5202 Broadband Strategies Handbook