In this paper, we present a modeling of transmission lines performed under real-world conditions to compare them with a theoretical transfer function. This model is based on the practical case of implementation for access networks "last mile" in rural areas, designed and implemented by National Telecommunication Corporation (CNT-Ecuador) at Azuay-Ecuador. In this sense, we review some theoretical concepts on evolution over time in xDSL technologies implemented by the company CNT-Ecuador. Then, we perform several field data analyses using measuring instruments, where electrical parameters were obtained with which we perform the modeling. In addition, it was realized an analysis and comparison of the obtained real capacities of transmission lines, against the theoretical ones by means of the Theorem of Shannon-Hertly for lines with VDSL technology. Into the outdoor tests and simulations, the data obtained allowed us to drastically correct the transfer functions of the lines in poor condition, through varying the most impacting electrical parameters. We present the results in a table with the ranges of the parameters that can be taken as reference so that a pair of copper wires operating in poor condition in rural areas, can work correctly with VDSL technology.