Frequency Domain Reflectometry Based SELT Approach for Loop Topology Estimation

Network operators need to ascertain loop topology before committing for the performance of a digital subscriber loop. Single Ended Loop Testing (SELT) is generally the most preferred and economical way for estimating the loop topology. In this paper we propose a novel method of loop topology estimation based on discrete multitone line code which reuses most of firmware modules in a typical DSL broadband modem. The loop estimation is done in two phases, the first being frequency domain reflectometry data collection phase and the second being an analysis phase which is done in time and frequency domains. Three types of topologies are considered in this paper for validation: a single line, a network with bridge tap and a cascade of two line sections. The major advantages of this method are, no prior knowledge of the network topology is required, all code is resident in the modem itself and does not need any external bypasses. This method shows good prediction capability for all types of networks up to 20 Kft.