Leased Circuits Research Articles

Small Delay and High Performance AD/DA Converters of Lease Circuit System for AM&FM Broadcast

Many AM&FM broadcasting stations in Japan are connected by the leased circuit system of NTT. Small delay and high performance AD/DA converter was developed for the system. The system was designed based on ITU-T J.41 Recommendation (384kbps), the transmission signal is 11bit-32 kHz where the Gain-frequency characteristics between 40Hz to 15kHz have to be quite flat. The ΔΣAD/DA converter LSIs for audio application in the market today realize very high performance. However the performance is not enough for the leased circuit system. We found that it is not possible to meet the delay and Gain-frequency requirements only by using ΔΣAD/DA converter LSI in normal operation, because 15kHz the highest frequency and 16kHz Nyquist frequency are too close, therefore there are aliasing around Nyquist frequency.In this paper, we designed AD/DA architecture having small delay (1msec) and sharp cut off LPF (100dB attenuation at 16kHz, and 1500dB/Oct from 15kHz to 16kHz) by operating ΔΣAD/DA converter LSIs over-sampling rate such as 128kHz and by adding custom LPF designed Infinite Impulse Response (IIR) filter. The IIR filter is a 16th order elliptic type and it is consist of eight biquad filters in series. We described how to evaluate the stability of IIR filter theoretically by calculating frequency response, Pole and Zero Layout and impulse response of each biquad filter, and experimentally by adding overflow detection circuit on each filters and input overlord signal.

The regional cost gap of the Japanese local telecommunications service

Abstract. The focus of the Japanese local telecommunications policy is shifting towards solving the problem of the digital divide that accompanies the spread of high‐speed and broadband services. The article estimates a translog cost function of two outputs – the standard telephone service and the leased circuit service – and measures the regional gap of those stand‐alone costs and incremental costs. The main point we make is that the cost gap for the leased circuit service is larger than that for the standard telephone service among the 11 Nippon Telegraph and Telephone (NTT) regional offices.

A pilot study of low-cost dynamic telepathology using the public telephone network.

A pilot trial of a low-cost telepathology system was conducted. A video-codec operating to the CIF standard was used to transmit pictures over the public telephone network. Twenty-seven specimens from the routine pathology workload of a district hospital were examined. The average length of time spent examining each specimen was 14 min (range 2-40). The telepathology diagnoses were judged by conventional light microscopy of the specimens, performed by the same observer at a later date, and by a different observer. For the same observer, 23 diagnoses were correct (85%) by telepathology, three were acceptable (11%) and one was incorrect (4%). The results were slightly worse for a different observer: 21 diagnoses were correct (78%) by telepathology, five diagnoses were acceptable (19%) and one diagnosis was incorrect (4%). The technique was slower than conventional dynamic telepathology (such as that based on communication by ISDN or leased circuits) and picture quality was poor by comparison. However, these are not necessarily disadvantages in the context of the developing world, and since only a telephone connection is required, the technique could become an important method of improving the distribution of scarce resources, such as pathology expertise.

Report of a national neurosurgical teleradiology system.

An emergency neurosurgical teleradiology system was initially installed in two referring hospitals in ireland to transmit images to the neurosurgical department in Cork. It was subsequently expanded to six major referring hospitals transmitting to both neurosurgical departments in ireland serving the entire population of 3.5 million people, effectively becoming a national teleradiology system. The system was based on PCs interconnected by leased data circuits and ISDN. The network was operational 24 hours a day. Over 750 emergency computerized tomography scans were transmitted and transmission failures occurred in only 6% of cases. We conclude that current PC technology can be used to form a peer-to-peer wide-area network upon which a robust emergency teleradiology system can be based.

North Dakota: Connectivity and cooperation

North Dakota has in place a telecommunications infrastructure that is advanced and active, given the state's rural nature and large pockets of low population communities. The state is criss‐crossed by fiber‐optic cables that link the majority of telephone central offices to each other and connect clusters of high schools with interactive video networking. Public television stations are available in most communities of the state. State government is among the leaders in the state in the rapid deployment of frame relay services. The frame relay network represents the newest generation of data communication facilities in North Dakota, replacing a statewide network of dedicated leased data circuits and X.25 packet switches. The frame relay system provides each user group on the network with a Virtual Private Network (VPN) for data communications, which is transparent to other users on the network.

Congestion control in IP/TCP internetworks

Congestion control is a recognized problem in complex networks. We have discovered that the Department of Defense's Internet Protocol (IP), a pure datagram protocol, and Transmission Control Protocol (TCP), a transport layer protocol, when used together, are subject to unusual congestion problems caused by interactions between the transport and datagram layers. In particular, IP gateways are vulnerable to a phenomenon we call congestion collapse, especially when such gateways connect networks of widely different bandwidth. We have developed solutions that prevent congestion collapse.These problems are not generally recognized because these protocols are used most often on networks built on top of ARPANET IMP technology. ARPANET IMP based networks traditionally have uniform bandwidth, identical switching nodes, and are sized with substantial excess capacity. This excess capacity, and the ability of the IMP system to throttle the transmissions of hosts has for most IP/TCP hosts and networks, been adequate to handle congestion. With the recent split of the ARPANET into two interconnected networks and the growth of other networks with differing properties connected to the ARPANET, however, reliance on the benign properties of the IMP system is no longer enough to allow hosts to communicate rapidly and reliably. Improved handling of congestion is now mandatory for successful network operation under load.Ford Aerospace and Communications Corporation, and its parent company, Ford Motor Company, operate the only private IP/TCP long-haul network in existence today. This network connects six facilities (one in Michigan, two in California, one in Colorado, one in Texas, and one in England) some with extensive local networks. This net is cross-tied to the ARPANET but uses its own long-haul circuits; traffic between Ford facilities flows over private leased circuits, including a leased transatlantic satellite connection. All switching nodes are pure IP datagram switches with no node-to-node flow control, and all hosts run software either written or heavily modified by Ford or Ford Aerospace. Bandwidth of links in this network varies widely, from 1200 to 10,000,000 bits per second. In general, we have not been able to afford the luxury of excess long-haul bandwidth that the ARPANET possesses, and our long-haul links are heavily loaded during peak periods. Transit times of several seconds are thus common in our network.Because of our pure datagram orientation, heavy loading, and wide variation in bandwidth, we have had to solve problems that the ARPANET/MILNET community is just beginning to recognize. Our network is sensitive to suboptimal behavior by host TCP implementations, both on and off our own net. We have devoted considerable effort to examining TCP behavior under various conditions, and have solved some widely prevalent problems with TCP. We present here two problems and their solutions. Many TCP implementations have these problems; if throughput is worse through an ARPANET/MILNET gateway for a given TCP implementation than throughput across a single net, there is a high probability that the TCP implementation has one or both of these problems.

Network configurations for leased circuits in metropolitan areas

With the rapidly increasing demand for leased service, an important issue in the future telecommunication network will be efficient utilization of leased circuits. This paper considers the network configuration for leased circuits in the metropolitan area, where the demand for such circuits is increasing. This paper also discusses the allocation of cross-connect (XC) nodes in the construction of the network for low-speed leased circuits and the segregation/sharing of public and leased circuits from the viewpoint of economy. First, the system configuration for the low-speed leased circuits and the network topology for the efficient operation of the leased circuits are discussed. As a result, allocation schemes for XC nodes and schemes for fiber segregation and transmission capacity are proposed. Then the relation between the number of XC nodes and the network cost, as well as the relation between the transmission capacity and the network cost, are discussed from the viewpoints of the segregated and the shared configurations for the leased and public circuits. From this discussion, the optimal XC node allocation and the optimal transmission capacity are shown. Finally, a comprehensive assessment is described and the optimal area for each of the proposed network configurations is shown quantitatively for the case where the demand for the leased circuit or the equipment cost is varied.

Deployment of ATM subscriber line systems

A B-ISDN introductory scenario is described from the viewpoint of service, and a virtual-path (VP)-based access network architecture based on this scenario is discussed. In the access network each VP is dedicated to one service, such as a leased circuit, switched circuit, or video distribution. The concept and functions of a subscriber line terminal (SLT) to realize this capability are introduced. Asynchronous transfer mode (ATM) subscriber line system deployment and the main SLT functions are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multimedia multipoint teleconference system using the 7 kHz audio coding standard at 64 kbit/s

The International Telegraph and Telephone Consultative Committee (CCITT) has recommended an algorithm to code wideband speech and music (i.e. 7-kHz audio) with 64 kb/s as an international standard (recommendation G.722). A multimedia multipoint teleconference system using the 7-kHz audio coding standard is discussed. System requirements for teleconferencing are examined, and control procedures for the system are examined. A system using digital leased circuits is presented, and the audio-bridging technique used in this system is discussed. >

Packet Radio Alarm System on Voice Dispatch FM Mobile Radio Channels

Packet radio can be used by electric utilities to cammunicate substation alarm data, serving as a reliable and economic alternative to leased telephone circuits. This paper details the application, design and usage of such a system on existing company FM 2-Way radio voice channels. The recent availability of commercial packet radio modems, along with specialized computer software designed by the authors, is the cornerstone for this system. By utilizing computers with 16 point input or output ports, these units can also be used for packet radio control links.

Present Trends in High-Speed and Broad-Band Communications Services in Japan

This paper describes present trends in high-speed and broad-band communications services in Japan. It gives an overview of video, high-speed digital leased circuit and satellite digital communications services, and gives examples of their applications. Recent trends in telecommunication services and technology are described, including video conferencing services presently available in more than ten cities throughout Japan, as well as a video response system which is about to be put into service. It also describes the present status of Japan's cable television (CATV) system and discusses its future development. Finally, NTT's plans for high-speed and broad-band communications service in the future are previewed.

Design and Architecture of the High-Speed Digital Data Transmission System in NTT

Demand for high-speed wide-band telecommunication services is rapidly growing due to the remarkable progress in office, factory, and laboratory automation. These services are expected to be first introduced in leased circuits and then extended, to high-speed switched services. This paper presents the users' demands for such high-speed services and the NTT design concepts for the high-speed digital data transmission system (HDDTS) in NTT to provide such high-speed leased circuit service. The ISDN user-network interface is adopted. The basic high-speed pointto-point transmission service started in October 1984, and enhanced leased circuit service involving multiplexed interfaces and muitipoint circuits will be introduced in the fall of 1985.

Congestion control in IP/TCP internetworks

Congestion control is a recognized problem in complex networks. We have discovered that the Department of Defense's Internet Protocol (IP), a pure datagram protocol, and Transmission Control Protocol (TCP), a transport layer protocol, when used together, are subject to unusual congestion problems caused by interactions between the transport and datagram layers. In particular, IP gateways are vulnerable to a phenomenon we call congestion collapse, especially when such gateways connect networks of widely different bandwidth. We have developed solutions that prevent congestion collapse. These problems are not generally recognized because these protocols are used most often on networks built on top of ARPANET IMP technology. ARPANET IMP based networks traditionally have uniform bandwidth, identical switching nodes, and are sized with substantial excess capacity. This excess capacity, and the ability of the IMP system to throttle the transmissions of hosts has for most IP/TCP hosts and networks, been adequate to handle congestion. With the recent split of the ARPANET into two interconnected networks and the growth of other networks with differing properties connected to the ARPANET, however, reliance on the benign properties of the IMP system is no longer enough to allow hosts to communicate rapidly and reliably. Improved handling of congestion is now mandatory for successful network operation under load. Ford Aerospace and Communications Corporation, and its parent company, Ford Motor Company, operate the only private IP/TCP long-haul network in existence today. This network connects six facilities (one in Michigan, two in California, one in Colorado, one in Texas, and one in England) some with extensive local networks. This net is cross-tied to the ARPANET but uses its own long-haul circuits; traffic between Ford facilities flows over private leased circuits, including a leased transatlantic satellite connection. All switching nodes are pure IP datagram switches with no node-to-node flow control, and all hosts run software either written or heavily modified by Ford or Ford Aerospace. Bandwidth of links in this network varies widely, from 1200 to 10,000,000 bits per second. In general, we have not been able to afford the luxury of excess long-haul bandwidth that the ARPANET possesses, and our long-haul links are heavily loaded during peak periods. Transit times of several seconds are thus common in our network. Because of our pure datagram orientation, heavy loading, and wide variation in bandwidth, we have had to solve problems that the ARPANET/MILNET community is just beginning to recognize. Our network is sensitive to suboptimal behavior by host TCP implementations, both on and off our own net. We have devoted considerable effort to examining TCP behavior under various conditions, and have solved some widely prevalent problems with TCP. We present here two problems and their solutions. Many TCP implementations have these problems; &lt;i&gt;if throughput is worse through an ARPANET/MILNET gateway for a given TCP implementation than throughput across a single net, there is a high probability that the TCP implementation has one or both of these problems&lt;/i&gt;.

Tariffs and private networks

The use of private networks for voice and data communications has become widespread among large UK companies. The decision by British Telecom to raise the tariffs for the leased circuits used in these networks will make costing such an operation even more complex

Second liberalization in Japan

The Japanese government revised the Public Telecommunications Law and issued the relevant Act and Ordinance on 23 October 1982. Ten years have passed since the first liberalization opened up the public networks for data communication. The newly revised Law paves the way for more liberal use of leased circuits and networks from Nippon Telegraph and Telephone Public Corporation (NTT). Further, it permits activities of specialized telecommunications service agencies to compete with the government-owned and monopolized NTT in the domestic data communication market. Industrial and financial circles have demanded both, as they would like to spread their computer communication networks more extensively, and offer some specialized telecommunication services within their own community. The historical and social background to this remarkable liberalization were discussed in a recent article in Telecommunications Policy.

New LSI Digital Service Units and Office Channel Units Used for NTT Digital Data Networks

Digital data services have been offered by NTT since 1978. The largest part of the entire digital data network cost is attributable to subscriber loop transmission that includes digital service units (DSU's) and office channel units (OCU's). Therefore, it is important to reduce DSU and OCU costs for economizing on digital data services. In order to achieve this purpose, new LSI DSU and OCU have been developed. The LSI is used for a digital signal processing unit, which occupies most of the equipment cost and size. The LSI can be applied to all bearer rates from 3.2 to 64 kbits/s, for NTT digital data services (leased circuit service, circuit switched service and packet switched service). It is highly significant that adoption of the LSI in DSU and OCU makes the following estimations feasible: 1) About 30 to 40 percent Cost reduction 2) About 25 percent size reduction 3) About 30 to 50 percent failure rate reduction 4) About 50 to 70 percent power consumption reduction. Summary The most expensive part of the network that carries NTT Digital Data Services is the subscriber loop transmission system, which includes DSU and OCU. This paper describes the design philosophy for introducing LSI technology in the DSU and OCU for cost reduction. Then the function, construction and evaluation are presented for the newly developed LSI DSU and OCU, based on the above design concept.

Computer Control of Gas Transmission

Abstract The Alberta Gas Trunk Line Company Limited are now completing an automation program which permits basically " unattended" operation of field facilities. Gas receipts and deliveries are controlled from a Dispatch Centre in Calgary. A dispatcher obtains required gas flows into the system by the issuance of flow orders to the producers. Gas transmission and deliveries are controlled by the dispatcher's issuance of telemetered commands to field equipment. A supervisory system has been installed, consisting of master station equipment in the Dispatch Centre and remote supervisory panels at major field facilities. Telemetering is accomplished over leased circuits that are also used for voice communication. The supervisory system gathers and stores field data from major receipt, transmission and delivery points. It alerts the dispatcher of abnormal conditions requiring his attention. It performs computations and displays information to assist the dispatcher in proper courses of action. The supervisory system also enables the dispatcher to implement commands directly to field equipment. The computer is an integral part of the supervisory system. It performs many supervisory functions that alternatively would require hard wired equipment, and is justified by these savings alone. The computer's computational and storage abilities also provide information that would be impractical to obtain by other equipment. A third advantage of the computer is the flexibility of its operation, which allows many modifications and additions to be made by minor program changes. The computer currently performs many tasks, but it is still idling much of the time. New assignments are being written, and it is expected that the computer will play a larger role in years to come. The automation of its facilities is enabling Alberta Gas Trunk Line to cope with a rapidly expanding system, and is resulting in a better and more efficient operation.

Pilot-wire protection of transmission lines

THE PRESENT pilot-wire protective systems for transmission lines employing leased pilot-wire circuits are an outgrowth of conventional differential protective systems for other types of electric apparatus. Thus, these line-protective systems are characterized by the fact that the pilot wires are part of the differential connection between the current transformers at the line ends. The pilot wire has distributed shunt capacitance as well as series resistance, with the result that when these parameters reach sufficient magnitude, attenuation and undesirable phase shifts occur in the pilot-wire circuit. Thus, the system may be prevented from functioning correctly under certain operating conditions.

Protective Relaying Systems Using Pilot-Wire Channels

This paper has presented a variety of pilot-wire relaying systems. Each has its field of application which is influenced by technical and economic factors, as listed in the previous section. In many cases, particularly where tapped or multiterminal lines are concerned, combinations of the various systems will be necessary for high-speed simultaneous clearing of faults. Experience has indicated that well-designed private-wire circuits are likely to be more reliable than leased circuits. A basic reason for this is the difference in philosophy between communication and power system engineers as to what constitutes a reliable channel. However, given a specific channel, there are no significant differences in the expected reliability of the vanrous relaying systems. The reliability and security of pilotwire relaying can be improved by the following: 1. The use of fault detectors to supervise conventional a-c pilot-wire relay tripping, where their use will not compromise the relay system performance. 2. Supervision of the receiver-relay contact of the transferred-tripping schemes by fault detectors. 3. Channel-failure supervision of the trip circuit with blocking schemes. Table III gives the salient features of the pilot-wire relaying systems described in this paper.

A portable telegraph bias and distortion measuring instrument

IN THE modern telegraph system, signals are transmitted over various trunk facilities derived from wire lines or radio relay systems. The trunk telegraph channels furnish facilities between a number of switching centers located at strategic points throughout the country. These centers then distribute traffic to the local points of destination. In addition, various other services must be accommodated by suitable network configurations. These services comprise such arrangements as are involved in leased network circuits, private switching systems, etc. It is necessary that flexibility be maintained in this complex network of circuits so that circuit patching and routing may be accomplished without making undue alignment changes in the circuits themselves.