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Chapter 2Overview of current CATV network pDue to a high installation cost involved, the initial structure may not be point-topoint.However, using a Passive Optical Network (PON) and passive optical couplersto split fibres from the Headend to the home into multiple fibres reduces the numberof laser transceivers required for every home, and in turn reduces the cost ofdeployment. Bi-directional communication over FTTH networks is achieved by aMAC protocol that shares bandwidth on the PON structure among different homeservers [75].• SuperPONs: Super Passive Optical Networks (SuperPONs) is another alternativetechnology in its early stages, which can be applied to FTTC and FTTH networks[81]. This technology is considered as the next generation PONs, designed to rungreater distances (about 60 miles) and can support a larger number of users (up to2048 ONUs). SuperPONs provide shared bandwidth up to 2.5G bps downstreamusing TDM and 311 Mbps upstream with TDMA. The major technical challenge insuch architectures is the development of a MAC protocol that could allow fair accessto the network by such a large number of users.2.7.2 xDSL technologiesxDSL is a series of Digital Subscriber Line technologies which allows for thetransmission of information (voice, video and data), over existing copper telephonelines at high speeds. The xDSL technology is attractive, since there exists a hugeinstalled base of twisted pair lines (800-million) worldwide [26]. Optical fibre will carrysignals from a central office to a neighbourhood node, which in turn converts the signalsand puts them into a telephone line to the user. In some cases, a direct copper line canbe used if the distance from the central office to the user is not too large (usually under4 miles). DSL has a similar problem to cable modem technology; upstream bandwidth ismuch smaller than downstream (except its symmetric system which is much moreexpensive). There are various forms of DSL, referred to as xDSL.• ADSL: Asymmetric Digital Subscriber Line (ADSL) is quickly becoming the mostpopular form of xDSL. ADSL can support up to 8 Mbps bandwidth for downloadingand up to 640 kbps for uploading [6].2-16