The use of existing metallic local line facilities is being studied for the provision of high-speed digital transmission services. Local line characteristics have to be modeled in the form of the objective requirements that should be met by DSL for estimating the feasibility of the service provision in the actual network. This paper presents the results of a study that models the metallic media characteristics of NTT's local network. First, the line lenghts determined by the existing local line deployment rule and the cable types used in the networks are introduced. Second, the values of crosstalk characteristics, the most significant factors in limiting DSL range, are given by classifying essential line conditioning states of each cable. The values of crosstalk characteristics are newly computed by taking into account detailed cable pair-binding (cabling) structures, and the worst case values among all possible combinations of multiple inter-pair interfering-interfered relationships within a cable are given though a previous study approximated cable pair-binding structures. The crosstalk characteristics of NTT's and American local networks are also compared. A modified approximate equation of line propagation characteristics is also proposed for representative local lines, and its precision is verified by comparing simulation results to actual measurements in both frequency and time domains.

This paper presents the results of a study made to determine the line length coverage of the high-bit-rate digital subscriber line (HDSL) present in NTT's local networks. The HDSL carries one bi-directional 784 kbit/s channel per pair and supports the digital interface at 1544kbit/s by using two cable pairs. The primary purpose of this study is to estimate the range limits for candidate transmission schemes considering line installation conditions, and to determine the most promising transmission scheme and its feasibility given the environment of NTT's local networks. Pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM) transmission schemes are compared for HDSL implementation. It is shown that 2B1Q-PAM and 16-QAM generally achieve better performance than the more complicated PAM and QAM given the presence intra-system crosstalk interference (interference between identical transmission systems). The range limits determined by inter-system crosstalk interference (interference between different transmission systems) with basic rate access (BRA) implementing a burst-mode transmission method are also estimated. This paper concludes that 2B1Q-PAM achieves the best overall performance in NTT's local networks. A feasibility study of 192-6144 kbit/s transmission is also described.