ITU-T addresses HFC networks

BY STEPHEN C. METTLER

The ability to deliver "broadband to the customer" has been a major motivation in the development of fiber-optic networks. Because the last mile is primarily served by copper cable-coax or twisted-pair-an economically feasible approach has been to use hybrid fiber/copper (HFC) systems. In the cable television world, the "C" in HFC usually stands for coax, while in telecommunications, it stands for copper twisted-pair. HFC systems can be used for both TV distribution and new telecom services. Field trials of various HFC systems have been ongoing projects throughout the world.

Study Group 6 (Outside Plant) of the International Telecommunication Union's Telecommunication Standardization Sector (ITU-T) studied these HFC systems under question Q.13/6 during the 1996-2000 study period. Its objective was to produce a new Recommendation dealing with the outside plant for cable TV applications up to 1 GHz and narrowband and broadband transmission systems as defined by Study Group 15. The following points were studied:

  • Topology of the network.
  • Cable construction.
  • Cable accessories and components.
  • Comparison of the different installation methods in relation to costs and installation time.

Results of this study, led by Edoardo Cottino (SIRTI, Italy), with assistance from yours truly, produced ITU-T Recommendation L.47, "Access facilities using hybrid fiber/copper (HFC) networks."

L.47 gives general information on the fundamental types of hybrid fiber/copper networks, describes the most important physical elements of HFC networks apart from transmission equipment, and gives general information and guidelines for the installation of HFC networks. The appendices provide responses to a questionnaire on HFC networks from a number of different countries as well as descriptions of field experience from Italy and Indonesia.

Through its IPCablecom initiative, ITU-T Study Group 9 is developing a coordinated set of Recommendations that will specify an architecture and a set of integrated protocol interfaces that operate as a system to enable the efficient delivery of voice, video, and Internet over HFC networks using IP.


Stephen C. Mettler, recently retired from Bell Laboratories, is an independent consultant on outside plant and other issues in optical-fiber communications and represents OFS on Study Group 6 of the ITU-T. He can be reached at 404-262-1867 or smettler@bellsouth.net.

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