A line terminating LSI using echo cancelling method for ISDNsubscriber loop transition

A 144-kb/s digital subscriber loop (DSL) transmission system based on hybrid transmission with an echo cancelling method is described. It incorporates advanced LSI technology to obtain compactness, low cost, and high reliability. An echo canceller (EC) LSI has been developed using CMOS technology. Combined with the multiplexing processor (MXP) LSI, the EC LSI provides basic DSL equipment functions. A specially arranged frame format with a newly developed digital phase-locked loop (DPLL) circuit for stable timing extraction, an automatic balancing network, and a two-stage echo canceller characterize the system. Using this line termination circuit, the DSL equipment showed a reach of over 6 km when used with 0.5 mm diameter cable for 160-kb/s bidirectional digital transmission     

A floating, low-power subscriber line interface circuit [bipolar IC technology]

A subscriber line interface circuit is described which is smaller than and dissipates substantially less heat than conventional circuits which perform similar functions. Worst case heat dissipation in the circuit is only 0.65 W as compared to conventional arrangements which dissipate up to 4 W. The battery feed function is accomplished by a small 1.5 W DC-to-DC converter which also includes circuitry for detecting loop supervisory functions. The floating nature of the output circuitry renders it immune to power line induction and common mode power crosses. Primary protection from lightning and other induced surges utilizes conventional carbon block type protectors. Secondary circuit protection is accomplished with a high voltage diode and simple carbon composition resistor. Circuit disconnect is accomplished with a medium voltage SCR for ringing and loop testing the subscriber line. The battery feed control and loop supervisory functions have been realized in a low voltage, linear integrated circuitry using CBIC technology.     

Rural Subscriber Physical Loops

This paper briefly traces the development of physical subscriber loop design in the Rural Electrification Administration (REA) Program from 1949 to the present. Development of equipment for overcoming in the most economical manner the signaling and transmission problems encountered with long subscriber loops is also discussed. This includes loading systems for wider bandwidth, better structural return loss, less bridging effects with multiparty lines; loop extenders in place of costly long-line adapters (LLA's); lower cost voice-frequency repeaters (VFR's) and switching methods such as Common-Mode Operation (CMO) where less equipment is required. Discussion of the problems still encountered with transmission and signaling on rural subscriber loop is presented with ideas for solution. Development of VFR equipment with automatic gain control for use in CMO or Common-Control Central offices would permit designing to common circuit net loss and minimize contrast between circuits. Extension of signaling limits of central office equipment (COE) now being developed could eliminate the need for external loop extension equipment on better than 90 percent of rural subscriber loops. Development of a telephone instrument requiring less dc line current would eliminate the need for elevated line voltages.     

A switching regulator and lightning protector for a subscriber line interface circuit

Two monolithic ICs, a switching regulator and a crowbar protector circuit fabricated in a 90-V complementary bipolar technology are described. These devices enhance the performance of a basic subscriber-line interface circuit (SLIC) by extending the range to the customer so that 20-mA DC feed current can be supplied to a 2800-/spl Omega/ loop without the need for a -72-V office battery. The power dissipation of the entire SLIC subsystem is at most 1.5 W for any length of subscriber loop. All circuitry is robustly protected from foreign 60-Hz and lightning voltages.     

Line Circuit Interfaces for a Digital Switching System

Crucial to the design of digital switching systems for local switching applications is the line circuit interface. It forms the boundary between the analog, 2-wire, subscriber loop, with its attendant environment hostile to low-voltage electronics, and the digital logic environment. ITT North's DSS uses a Quad Line Circuit (QLC) that provides the line circuit interface between four subscriber loops and two PCM multiplexed highways. The QLC contains per-line elements consisting of an electronic 2W/4W hybrid, transmit and receive PCM filters, a codec, two card-mounted relays, and distributed logic for various gating and clocking functions. In addition, there is digital logic common to all four lines for interfacing with redundant microprocessors common to 320 lines. Design of the QLC in a dynamic technology evolution is discussed, and several evolutions of the initial design are presented.     

A Subscriber Carrier System Based Upon Frame Addressing System

A new channel assignment scheme called a frame addressing system is proposed in this paper to realize an efficient telephone subscriber carrier system by means of PCM loop having a simplified switching capability at each subscriber. In the frame addressing system, a speech signal time slot is assigned by sending a bit for each subscriber at the beginning of each transmission frame. This results in an improvement of efficiency by a TASI-like effect in addition to efficiency by switching. The principle and an example of a practical circuit are described. Characteristics of the system are analyzed and a design example is described.     

A Line Termination Circuit for Burst-Mode Digital Subscriber Loop Transmission

This paper describes a line termination circuit for burst-mode bidirectional digital subscriber loop transmission. It incorporates the most advanced LSI technology to obtain compactness, low cost, and high reliability. Two CMOS LSI's have been developed; one is a line termination LSI (LT) and another is a circuit termination LSI (CT). LT LSI adopts a novelRCactive filter-type equalizer and decision feedback bridged tap equalizer suitable for incorporation in LSI and provides high performance. By using these LSI's, a line termination circuit realizes a reach of over 5 km at 88 kbit/s bidirectional digital transmission. This paper describes each LSI and shows total performance characteristics in detail.     

Timing Jitter Effects on Digital Subscriber Loop Echo Cancellers: Part II--Considerations for Squaring Loop Timing Recovery

The performance of an adaptive echo canceller at the looptimed subscriber end of a digital subscriber loop has been shown to be sensitive to jitter arising from the timing recovery subsystem. We evaluate this degradation for the common timing recovery subsystem consisting of a prefilter, a squarer, and a second-order phase-locked loop. The evaluation shows the influence of equalization, prefilter shape, and phaselocked loop parameters. A narrow-band accurately tuned prefilter, line equalizer, and a narrow-band phase-locked loop are found to be necessary for adequate performance in a 144 kbit/s bipolar-coded digital subscriber loop system employing echo cancellation.     

A High Voltage Line Driver for Subscriber Loop Interfaces in a Low Voltage Submicron BiCMOS Technology

This paper presents a 30 V line driver for short loop subscriber line interface circuit applications. The high voltage line drivers was implemented in a low-voltage 0.8 m BiCMOS process using 30 V extended-drain MOS transistors, fully compatible with the low voltage technology. Using a Quasi-Current Mirror architecture for the output stage, the line driver is capable of delivering more than 30 mA current into the lines with an idle current as low as 1 mA, satisfying the short loop requirements. With less than 0.24 mm² area, the circuit can be easily integrated with low-voltage circuitry on a single chip.     

非对称数字用户线语音分离器设计

非对称数字用户线技术是目前用户连接互联网最重要的方式之一。文章对非对称数字用户线的技术特点和标准进行了系统的介绍．并分析了语音分离器原理和必备的技术指标，设计了一个语音分离器并进行了系统仿真测试。     

ISDN-Oriented Modular VLSI Chip Set for Central-Office and PABX Applications

This paper describes a new ISDN-oriented modular (IOM®) architecture developed to establish the subscriber basic access to an Integrated Services Digital Network in a central-office or PABX environment with a minimum number of VLSI circuits. A four-component VLSI chip set is presented, consisting of the S-bus interface circuit (SBC), the ISDN burst transceiver circuit (IBC), and the ISDN echo cancellation circuit (IEC) for layer 1 data transmission at the fourwireSand the two-wireUinterface, respectively, and the ISDN communication controller for layer 2 link access protocol control. The development strategy, the functions of the IC's, and examples for their application in the subscriber terminal and digital subscriber line board are emphasized.     

A 3-V CMOS low-distortion class AB line driver suitable for HDSLapplications

A fully differential CMOS line driver for use in high bit-rate digital subscriber line (HDSL) services Is presented. The circuit is fabricated in a single-poly quad metal 0.35-μm process and achieves <-70-dB total harmonic distortion while driving up to ±2.4-V, 200-kHz signals into 30 Ω with a 3-V supply. The circuit features a closed loop gain of 6.0 with minimal input capacitance (<200 fF). The circuit requires less than 20 mA of quiescent current and is capable of delivering dynamic currents as large as 180 mA. The circuit is a multistage amplifier utilizing nested-Miller compensation and an enhanced class AB output stage     

用于两个独立网的用户环路数字复接器

文章介绍用于两个独立网间的用户环路数字复接器，分析了用户环路数字复接器怎样在两个独立的拥有各自时钟的网间进行话音的传输。     

A long reach digital subscriber loop transceiver

An echo-cancelling duplex transmission system is described for the digital subscriber loop which uses a 4-level zero redundancy line code (2B1Q) to give very long reach in the presence of crosstalk. Novel digital signal processing algorithms are used to simplify the analogue line interface circuitry. All the digital signal processing, along with sophisticated maintenance and interfacing circuitry, can be contained on a single LSI circuit. Measured performance results are presented.     

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.     

Positioning the Subscriber Loop Network for Digital Services

The need to enhance the digital transmission capability of the local loop network to provide for new services is widely recognized in the telecommunications industry. Companies around the world [1]-[3] have been working towards this goal and plan to use digital loop carrier (DLC) to meet this demand. Although this approach is generally accepted, there has been little information presented on how to plan for the evolution of the local plant. To address these pressing issues, the Bell System is introducing a concept called fundamental subscriber carrier planning (FSCP). This paper discusses the impact that digital services will have on the subscriber loop network, including loop plant design requirements necessary to position the network for up to 64 kbit/s digital services. Existing cable plant has the capability to support most digital services, but there are specific design requirements that are quite different from those required for the "typical" analog voiceband service. This paper reviews the need to position the loop for digital services, and substantiates the major conclusion that digital loop carrier technology offers a significant advantage when provisioning for digital services.     

光纤数字用户环路系统

简要介绍了国际上光纤数字用户环路的发展概况及我们新近研究成功的光纤数字用户环路系统的原理、特点和功能     

Fiber-optic subscriber loop systems for integrated services--The strategy for introducing fibers into the subscriber network

Two approaches to fiber-optic subscriber loop system development in Japan are described. In the first. Approach I, NTT aims at introducing inexpensive fiber-optic subscriber loop systems using conventional LED's, multimode fiber, and analog transmission techniques in the near future. In the second, Approach II, fiber-optic subscriber loop systems will be made highly functional by evolving from analog to digital transmission. This paper presents system fabrication examples for each approach and the results obtained in the tests.     

An Approach to Multi-Service Subscriber Loop System Using Packetized Voice/Data Terminals

A new subscriber communication system and its design philosophy are described. In addition to telephone communication, the system is simultaneously able to offer data communication, still picture communication, etc. The system is composed of a packetized voice/data terminal, a multi-service switching equipment and the digital subscriber loop connecting between them. The system utilizes the existing subscriber line efficiently and is entirely suitable for coming telephone and data public digital network. 64 kbit/s PCM coded voice conversation and 48 kbit/s data communication were achieved simultaneously over 96 kbit/s digital subscriber line which was spanned up to 2 km.     

Digital optical CATV system using hubbed distribution architecture

A hubbed distribution architecture based on a bus-star configuration, three-level single single-mode fiber transmission using M-TPC line code, and high-speed IC technology is proposed. The architecture is cost-effective and compact. It is well suited to metropolitan area CATV systems and would allow a gradual transition to a broadband ISDN (integrated-services digital network) subscriber loop in the future. The proposed architecture is applied to a digital optical CATV system prototype. The equipment making up this system consists of a transmitter, hubs including video selectors, and subscriber unit. Two video channels are selected for each subscriber from eight video channels at hub stations. The transmission speed is 900 Mb/s, three-level for the trunk line and 200 Mb/s, three-level for each subscriber loop. Very compact and low-cost equipment is realized by using recently developed high-speed ICs. Experimental results show that the system satisfies requirements and that its commercial application is feasible