Changing the network structure: leaving the past behind

The infrastructure of the existing network is determined by the old copper access technology. Not only the copper access itself, also the number of central offices and their geographical distribution are results of the copper network and its physical limitations. Today, in Germany, several thousand active locations cater for the delivery of plain old telephony services, as well as for the delivery of new fiber-based broadband services. Due to the fact that the attenuation of optical fibers is relatively low, new concepts for the design of the network structure become possible and are discussed in this paper. A reach of 40 km, for example, on an optical transport system is no problem. Longer possible link lengths can result in a reduced number of central offices, leading to reduced expenditures for the building, power supply and air conditioning. In the case of Germany a number of some hundred central offices is envisaged. However, a significant drawback of today's existing optical access technologies is the very limited number of customers on a single fiber. For instance, GPON (Gigabit Passive Optical Network) provides typically a 32-way split and a distance of 20 km. This paper discusses some new ideas to introduce higher splitting ratios and longer access lengths into the network. With WDM (Wavelength Division Multiplexing) and/or coherent optical receivers new options for a future proof access network are available.