Architecture repartitioning to simplify outside-plant component of fibre-based access system

摘要

An improved access system for use in a Fiber-In-The-Loop (FITL) communications network is disclosed. The access system comprises a host digital terminal (HDT) and a plurality of subtending optical network units (ONUs). The digital signal processing (DSP) functions traditionally executed by line interface units (LIUs) within the ONUs are migrated to the HDT, rendering the individual ONUs simpler, cheaper and more reliable. This is made possible by the provision in each ONU of an oversampling codec for sampling (and conversion) of upstream and downstream data at a very high bit rate. The large bandwidths of the data communicated between the ONUs and the HDT are easily handled by the fiber optic medium therebetween. In the HDT, DSP functions are executed by a common pool, or bank, of DSP ASICs. Decimators are provided in the HDT in order to properly format the data for processing by the DSPs. Interpolators are provided in the HDT for creating a high rate bit stream that can be easily converted to analog format by a codec. A high degree of processing efficiency can be achieved by reducing complex processing tasks to a sequence of individual steps through the DSP bank and rerouting the result of each step through the bank. Such "hair pinning" can be performed in either the upstream (subscriber-to-core-network) or downstream (core-network-to-subscriber) directions. Optionally, decimators and interpolators can be provided in the LIUs.