This paper analyzed the connection points of Main Distribution Frames (MDF), which are installed between outside plants and inside plants (service nodes). This paper also proposes a connecting system for forthcoming FITL (Fiber In The Loop) networks. NTT has developed the Subscriber Line Cross-Connecting Module (LXM) for the FITL network and will continue to introduce LXMs and deploy optic subscriber networks in big cities throughout Japan.

A method is proposed for locating large gas leaks in subscriber cable networks composed of different type cables and/or branch cables that uses pressures periodically measured at several points. Theoretical pressure curves corresponding to these measured pressure curves are calculated using a model representing the actual cable network. These curves are called the calculated pressure curves. The position of the leak is varied in the calculation model and where the measured and calculated pressure curves coincide the most, the leak position in the calculation model indicates the estimated leak position. The calculated pressure curves are based on the Laplace transform and an analogy between the pneumatic characteristics in cable networks and the electrical characteristics in electrical transmission networks. An experiment using a cable network about 910m long resulted in a location error of less than 30m.

The use of existing metallic local line facilities is being studied for providing "video on demand (VOD)" services to residential subscribers across asymmetric digital subscriber lines (ADSL). ADSL carries a high-rate channel in the downstream direction from a central office (CO) to the subscriber, and a low-rate channel in both directions on an existing 2-wire pair. Audio and video signals are compressed by the moving picture experts group's standardized algorithms (MPEG 1 and MPEG 2), and delivered to the subscriber in the high-rate channel. Control (demand and response) signals are transceived in the low-rate channel. This paper presents the line length coverage of ADSL systems given the environment of NTT's local networks. The bit rates in the downstream and upstream directions are assumed to be 1.6-9.2Mbit/s and 24kbit/s, respectively. Two types of ADSL systems are considered: transceiving ADSL signals using the plain old telephone service (POTS) line or the basic rate access (BRA; 320 kbaud ping-pong transmission system) line on the same 2-wire pair. 16-QAM, 32-QAM and 64-QAM are compared as transmission schemes. Intra-system crosstalk interference (interference between identical transmission systems) and inter-system crosstalk interference (interference between different transmission systems) with the existing digital subscriber lines (DSL) are estimated. It is shown that the inter-system crosstalk interference with BRA is most stringent, and ADSL with 16-QAM yields the best performance in NTT's local networks. This paper concludes that realizing ADSL with 16-QAM can achieve channel capacities of up to 9.2Mbit/s for fiber-in-the-feeder (FITF) access systems, but the possibility of applying ADSL to direct access systems is remote except for a restricted short haul use. Some comparisons regarding American local networks are also described.

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.

Among various photonic switching technologies, photonic frequency division multiplexing technology is most promising. In this paper a novel photonic FDM (Frequency Division Multiplexing) system is proposed. The proposed system consists of n (multiplicity of frequencies) independent subnetworks, each of which is identified by a specific frequency, and of which each network topology is identical. When a connection is required by a terminal, the network selects a subnetwork that can afford it, and assigns a frequency representing the selected subnetwork to the terminal. This system eliminates frequency converting devices and traffic concentration equipment, which will reduce the size and cost of the system. A very small sized switching system of very large capacity will be easily realized. In this paper, first we will address the basic concept of the proposed system, and then discuss some technical problems and their solutions concerning network configuration, switch matrix structure, subscriber network configuration, control scheme and frequency multiplicity. Some experimental results are also mentioned.

This paper proposes a new subscriber distribution method called FTTA (Fiber To The Area), which uses millimeter-wave radio band to connect subscribers with base station and optical fiber to connect base station with control station in order to obtain broad-band transmission. Usually two main causes of signal degradation, i.e., rainfall attenuation on radio channel and intermodulation distortion on optical channel are considered in this system. Taking into considerations of these two factors, we analyze the available capacity of FTTA system for various 22nQAM modulation levels. The analysis clarifies that there exists an optimum modulation level that can maxize the available capacity, and AGC circuit in the base station is useful to compensate the rainfall attenuation. It is shown that 18.0Gbps is available under the optimum modulation method of the 64QAM with AGC and 12.0Gbps under the 16QAM without AGC when 20 carriers are used.

A new type of synchronous code division multiple access (S/CDMA) scheme for optical subscriber systems is reported. Passive channel multiplexing is promising for optical subscriber systems because it realizes high system performance at low cost. Unfortunately, passive channel multiplexing suffers from phase differences among the upstream channels, and these differences prevent the usage of traditional synchronous CDMA techniques that reduce cross channel interference. This paper proposes the new technique of block-interleaving & redundancy code sequences to overcome this problem. This combination realizes S/CDMA even in the presence of phase differences and eliminates cross channel interference completely. Therefore, in an optical subscriber system using the new type S/CDMA, the bit error rate performance is independent of phase difference levels and the number of multiplexed channels.

We propose an integrated smart cable operation system and its architecture for the future cable network. In the proposed architecture, an application programs and various modules are loosely coupled using a cable operation system platform. We anticipate the task flows for the future optical cable network operation in order to realize the proposed system and architecture. Each task flow is broken down into "atomic tasks." The task flow can be changed easily by combining these atomic tasks. We use an object-oriented design for designing the cable operation system platform. As a first step towards the construction of the proposed system a pre-prototype system was constructed and the results are shown.

The construction of an optical subscriber loop and its operation system will be one of the most important infrastructures for the information society of the future. This paper presents a discussion of current and future service trends, the evolution of fiber-optic systems in the loop, and subscriber loop operation systems. Several operation technologies are also discussed which will enable the operation systems described in this paper to be constructed. Of these, the key technologies are an operation system architecture with flexibility, software technologies based on object-oriented design and programming, and automatic operation modules.

Fiber-optic subscriber loops are beginning to be constructed worldwide as an infrastructure for the 21st century. Making the most of the superior transmission capabilities of optical fiber cable, high-speed and broadband services such as so-called Broadband-ISDN (B-ISDN) services are expected to be achieved. We review current trends in fiber-optic systems and discuss how fiber-optic subscriber loops should be implemented from the points of view of services and technology. First, prospective services offered over fiber-optic subscriber loops and resulting requirements for such loops are presented. Various kinds of services produced through fiber-optic subscriber loops will further develop the information-oriented society and have a major influence not only on the industrial world but on family life as well. Next, basic concepts of totally fiber-optic subscriber loops and proposals for shifting from the existing metallic cable network to totally fiber-optic subscriber loops are discussed. In this regard, we must consider the advantages of optical fiber cables and improve upon the disadvantages of the existing metallic cable network. In particular, a Digital Loop Carrier (DLC) system or a Passive Double Star (PDS) have been proposed to shift from the existing metallic cable network to totally fiber-optic subscriber loops effectively and economically. Finally, line configuration topology and latest fiber-optic technologies such as high-count cable, construction techniques and operation systems for use in achieving totally fiber optic subscriber loops are shown. We believe a single star configuration is the most appropriate for totally fiber-optic subscriber loops.

This paper describes a method of evaluating operations effort for fiber optic subscriber loops, such as the Central Terminal/Remote Terminal (CT/RT) system, which can economically provide a variety of telecommunication services. Four system configurations with different operation procedures are evaluated by simulation. By evaluating the operating costs associated with service provisioning, it is shown that automatic distributing frames are cost effective in subscriber loops with CT/RT systems. Moreover, the most economical operation strategies for installing and extending subscriber boards are discussed in terms of facility and operations cost.

To describe the state of visual communications in the U.S., two words come to mind: digital and anticipation. Although compressed, digital video has been used in teleconferencing systems for at least ten years, it is only recently that a broad consensus has developed among diverse industries anticipating business opportunities, value, or both in digital video. The drivers for this turning point are: advances in digital signal processing, continued improvement in the cost, complexity, and speed of VLSI, maturing international standards and their adoption by vendors and end users, and a seemingly insatiable consumer demand for greater diversity, accessibility, and control of communication systems.