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In order to identify if a subscriber loop is suitable for a certain Digital Subscriber Line (DSL) service, the transfer function of the loop has to be estimated. Several measurement techniques exist, however Single-Ended Line Testing (SELT) is often preferred by the telecom operators because all necessary measurements can be done at the central office. The SELT data is typically interpreted in the time domain. This paper presents a new approach by doing the identification in the frequency domain. It starts by explaining the drawbacks of the time domain approach. The paper explains how these are avoided by using a frequency domain identification algorithm. Measurement results show this is a viable alternative to the classical time domain identification.

In order to accomplish the ever increasing demand of the user, new DSL technologies ('digital subscriber line') are developing. A lot of research is going on to use also the common mode signal beside the differential mode signal. This promising technique requires new reliable models. For the modeling good approximations for the series impedance are indispensable. In this paper a formula who calculates this impedance is presented and also validated with measurements.