Transport meets access: a strategy for the merger of transport and access networks

摘要

Currently, CATV coax networks are being upgraded with fiber to realize Hybrid Fiber Coax (HFC) access networks for digital video distribution and to carry bidirectional data and voice telecom services. Fiber feeders are deployed to expand the geographical area covered per headend, mainly by reusing the passive portion of the coas distribution segment for the new digital and bidirectional services in a fiber-to-the-curb topology. The differing signal formats standardized for the SDH/SONET core telecommunication network and for the access networks, however, leave some challenges for seamless, efficient and filexible interconnection of transport and access networks. When inserted into the coax cable, broadcast and dedicated data stream signals need to be modulated on a subcarrier according to cable standards. This implies the use of analog fiber feeders since conversion from (baseband) PCM format to multiple subcarriers on a channel-by-channel basis is not feasible at the numerous remote fiber/coax transitions inside the cabinets housing the Optical Network Units (ONU). On the other hand, analog feeders suffer from limited fiber span, noise accumultion and linearity requirements on components, and thus higher operation costs, compared with low-cost digital baseband (PCM) feeder lien equipment.