Time-Shared Two-Wire Digital Subscriber Transmission System and Its Application to the Digital Telephone Set

Adopting digital techniques in the local network area will enhance the possibility of extending digital operation capability to the subscriber's equipment. The problem is to convey digital signals at a bit rate of at least 64 kbits/s in both directions over existing two-wire subscriber loops. This paper describes a time-shared two-wire digital subscriber transmission system in which the directional separation of two signals (GO and RETURN) is accomplished by the time division bidirectional transmission method in burst-mode, and also reports results of investigations on the feasibility of an all digital telephone subscriber loop system.     

The Loop Coverage Comparison Between TCM and Echo Canceller Under Various Noise Considerations

This paper describes loop coverage evaluations of two-wire digital subscriber transmission systems to support the CCITT recommended 1-430 interface. Several range-limiting factors are discussed and a cable utility design for two representative two-wire digital subscriber transmission systems is presented. The two transmission systems are time compression multiplexing (TCM) and echo canceller (EC), utilizing the AMI line code and full cosine rolloff line equalization for both systems. A new impulse noise evaluation is applied to cable utility design, because impulse noise is one of the most stringent range-limiting factors, especially for TCM in utilizing existing subscriber loops. Comparison of TCM with EC is also carried out according to various range-limiting factors. As a result, it is noted that the 320 kbit/s line bit rate TCM is more applicable in NTT's exchange area coverage than the 160 kbit/s EC to achieve the2B + Dbasic interface transmission.     

ADSL: a new twisted-pair access to the information highway

The asymmetric digital subscriber line (ADSL) takes advantage of the existing twisted-pair copper loop that currently provides customer access to the telephone network. An ADSL modem is placed at each end of the loop to create a high speed access link above the existing telephone service. Since ADSL makes use of the existing copper telephone line, its application in the telephone network can conceivably be nearly as ubiquitous as the public telephone network itself. With ADSL, it is possible to connect small numbers of customers to broadband services in areas where full upgrade to hybrid fiber coaxial or fiber facilities is not economical in the near term. ADSL systems offer a means to introduce broadband services using the embedded base of metallic loops in areas where optic fiber-based, hybrid fiber-coaxial radio systems or other broadband transport systems may not be scheduled for deployment in time to meet business needs and customer demand. The article concentrates on ADSL systems capable of at least a nominal 6 Mb/s payload transport toward the customer, in addition to associated upstream channels and symmetrical “telephony” services via nonloaded loops that comply with carrier serving area design guidelines     

Implementation of a TDM passive optical network for subscriber loopapplications

An experimental prototype system for subscriber loop applications that has been implemented using a passive optical network architecture is described. The system, known as MACNET, uses time-division multiplexing and transmission over a network of single-mode optical fibers and couplers to provide narrowband digital service access to 16 customers. Experience gained from developing the system is outlined. Future transmission options, including a fixed-bit-rate customer access approach to allow early network application of this technology, are described     

A Tutorial on Two-Wire Digital Transmission in the Loop Plant

This paper explores the constraints on the design of twowire repeaterless digital subscriber loop (DSL) systems. Broadly categorized, the design depends on the technical feasibility of the approach used to achieve two-wire transmission, constraints related to compatibility with other systems sharing the same cable, and immunity to central office noise. Each of these varies With the choice of system parameters including the transmission rate, transmit power, choice of line codes, etc. Technical feasibility is evaluated by computer simulation studies. Compatibility with other systems is explored by crosstalk calculations. Noise immunity considerations, as they translate into digital line power levels, are also explored.     

The wireless art and the wired force of subscriber access

Different technologies for subscriber access are put side by side. Starting from the various transmission media characteristics of all systems, the well-known twisted pair lines with their corresponding digital subscriber line services are evaluated against wireless local loops, communications over ubiquitous power lines, high-bandwidth cable modems, and mobile radio. Each technology has its advantages and disadvantages. The different technologies will find their fields of applications. Most networks will have to provide a mixture of solutions for individual subscribers and customer segments to meet their boundary conditions. As a result, the future of subscriber access is a hybrid solution     

Timing Jitter Effects on Digital Subscriber Loop Echo Cancellers: Part I--Analysis of the Effect

We analyze the effect of Subscriber-end timing recovery Circuit jitter on the performance of two types of adaptive echo cancellers that can be used for full-duplex digital transmission on two-wire subscriber loops. Under severe echo-to-far-end signal ratios, echo canceller performance is found to be quite sensitive to high-frequency jitter components. Satisfactory performance with respect to jitter requires that a narrow-band phase-locked loop, rather than a single-tuned high-Qfilter, be employed for timing recovery.     

A monolithic telephone subscriber loop interface circuit

An integrated circuit that interfaces a subscriber loop with the digital telephone exchange has been produced with conventional high-voltage IC technology. The monolithic SLIC controls DC loop current, converts signal transmission from two-wire to four-wire, and suppresses longitudinal induction. Bias control circuitry automatically reduces standby power when subscriber equipment is detected on-hook. High-voltage circuit techniques maintain performance when the supply voltage exceeds the n-p-n transistor BV/SUB CE0/, and circuit partitioning with two discrete transistors yields manageable junction temperature and an economical 102/spl times/112 mil die size.     

Achievable information rates on digital subscriber loops: limitinginformation rates with crosstalk noise

The capacity and cutoff rates for channels with linear intersymbol interference, power dependent crosstalk noise, and additive white noise are examined, focusing on high speed digital subscriber line data transmission. The effects of varying the level of additive white noise, crosstalk coupling gain, sampling rate, and input power levels are studied in detail for a set of simulated two-wire local loops. A closed-form expression for the shell constrained Gaussian cutoff rate on the crosstalk limited channel is developed and related to the capacity, showing that the relationship between these two rates is the same as on a channel without crosstalk noise. The study also projects achievable rates on a digital subscriber line, inside and outside of a carrier serving area, with a sophisticated but realizable receiver     

Basic Principles of Digital Subscriber Sets

The introduction of digital exchanges into the local telephone network in the future will lead to the application of digital subscriber sets, where all speech and signal coding is carried out in the proximity of the telephone. In order to use the two-wire network the problems of digital transmission must be considered together with those of synchronization, signaling, speech conversion, and powering. This paper deals with the basic solutions and shows the concept for a first model of a digital subscriber set.     

Full-duplex data over local loops

An overview is provided of digital subscriber loops (DSLs), which are an essential part of the evolution from the integrated digital network (IDN) to the integrated services digital network (ISDN). Transmission impairments inherent in the subscriber loops are outlined, and their design is considered. Each of the essential elements in a DSL system is discussed in some detail, with emphasis on the tradeoffs of various design approaches     

Systems considerations for the use of xDSL technology for dataaccess

A variety of signal processing techniques have been developed over the past 10 years to increase the bit rate of digital transmission through telephone loop twisted pairs. The ISDN basic rate access 2B1Q digital subscriber line (DSL) was the first technology of this type to be deployed commercially at 160 kb/s full-duplex transmission on a single twisted pair. Other transmitter/receiver circuits have been developed over the years that support symmetric and asymmetric data transmission from several hundreds of kilobits per second to several megabits per second using the 2B1Q line code in the case of HDSL and various modulation techniques (QAM, CAP, and DMT) in the case of ADSL. These more recent forms of xDSL circuitry have begun to be used to provide commercial Internet access. This article analyzes the system level considerations for using these technologies in the increasing complex loop network of telephone companies. A “next generation” of xDSL access system is proposed, and the requirements for such a system are discussed     

基于HFC的宽带接入网关键技术

随着通信的发展和“信息高速公路”概念的提出,网络运营商越来越倾向集视频、话音、数据于一体的宽带综合业务,如今世界各国相继开发了基于现有铜缆的接入网技术高比特率数字用户环路(HDSL)和不对称数字用户环路(ADSL)、基于光缆接入技术的光接入网(OAN)、混合光纤同轴电缆(HFC)网络以及无线接入技术等宽带用户接入网技术,文章详细分析了HFC宽带接入网的网络结构及其关键技术。     

Loop Test System: A New Maintenance Feature for the Distributed Integrated Digital Network

The introduction of the digital Class 5 switch offers unique solutions to the requirements of growth and demands for improved service. For example, remote subscriber switches (RSS's) and subscriber carrier terminals (SCT's) can now be located near subscribers and digitally connected to the Class 5 switch via T1 repeatered lines or radio links. The result is shorter subscriber loops, improved transmission, and deferment or elimination of feeder plant additions. Traditionally, interposing electronics between the subscriber loops and the Class 5 switch resulted in isolating these loops from the office loop testing facilities. Remote testing of RSS and SCT assigned loops is an important step toward minimizing maintenance costs. Loop testing is accomplished in TRW Vidar's ITS5 switching system by locating loop test equipment in the remote RSS and SCT cabinets. This equipment is available to the test operator for real-time testing, and to the switch for automatic line testing. Some of the requirements that the loop test equipment must meet are: low cost, no adjustments, low power consumption, small size, operation in a harsh environment, and centralized testing capability from a test console. The data returned to the office must be in a quantitative form to allow further processing by the console. It must also be compatible with the direct distance dialing (DDD) network to allow transmission not only to the Class 5 switch serving the RSS and SCT, but also to distant service centers. This paper describes a newly developed system that meets the above objectives.     

Prediction of Crosstalk Involving Twisted Pairs of Wires-Part I: A Transmission-Line Model for Twisted-Wire Pairs

A transmission line model for predicting electromagnetic coupling (crosstalk) involving twisted-wire pairs (TWP) is developed. The twisted pair is modeled as a cascade of loops consisting of uniform two-wire sections with abrupt interchanges of wire positions at the ends of each loop. Experimental results are obtained for the coupling between a single wire above ground and a twisted pair above ground. The experimental correlation with the model predictions indicates that the simulation model is typically accurate within 3 dB for frequencies such that the total line length is less than 1/ 10 of a wavelength. For higher frequencies, the model tracks the experimental results quite well although the prediction error is somewhat larger.     

Echo Cancellation in Speech and Data Transmission

This tutorial paper reviews echo cancellation techniques as applied to both voice and data transmission applications. The echo control problem in telephone voice transmission is described, and the several measures taken to counteract echo are outlined. The problem of full-duplex data transmission over two-wire lines is described, with application to both digital subscriber loop and voiceband data transmission. The unique characteristics of each of these applications, more advanced methods recently proposed, and approaches to implementation are described.     

The ISDN U interface and transceiver

This paper describes the integrated services digital network (ISDN) basic rate interface (BRI) two-wire U interface and the transceiver necessary for the digital transmission of 160 kb/s of information over unshielded twisted pair transmission media. Topics discussed include the U interface structure and framing as described in the American National Standards Institute (ANSI) T1.601 specification, and the VLSI implementation of the ISDN U transceiver. Pertinent transceiver design issues addressed include the type of line code used, such as 2B1Q or 4B3T, echo cancellation, near end crosstalk, equalization and sampling rates.     

Digital subscriber line technology facilitates a gracefultransition from copper to fiber

The loop environment and the techniques that historically have been used for providing transmission treatment are reviewed. The digital subscriber line (DSL), which applies adaptive filtering to yield significant performance and administrative advantages, is introduced. How this technology will evolve to complement the emerging fiber-based network, providing timely, ubiquitous wire pair transmission capabilities at basic rate, primary rate, and above is examined     

A Time Compression Multiplexing System for a Circuit Switched Digital Capability

The time compression multiplexing (TCM) technique offers a solution to the problem of achieving digital penetration of the two-wire loop plant. TCM is planned to provide the digital loop transmission in the new circuit switched digital capability of the Bell System, so that a full-duplex 56 khit/s digital connection is obtained between subscriber's premises and the serving central office. Herein, the concept of TCM and its parameters are described. Tradeoffs leading to determination of system parameters such as burst frequency, burst length, guard time, and delay as they affect the range of the system are discussed. Also, the performance of the digital loops in terms of eye diagrams, system range limitations due to crosstalk and impulse noise, and percentage of loops covered are summarized. In addition, the circuit implementation using both analog and digital technologies is described. Experiences with various digital architectures to implement TCM and tradeoffs leading to a low-power digital architecture suitable for VLSI are discussed.     

Optical broadband access using ATM on a passive optical network

Within the framework of the ‘FITL (fibre in the loop) evolution’, Siemens is developing a prototype based on a passive optical network (PON) for the economic provision of BISDN services in the subscriber access area. It provides 32 subscribers with BISDN access up to a maximum user data rate of 45 Mbit/s per subscriber. The information is transferred via ATM cells and PON-specific overhead in both directions on the PON at a data rate of 155.52 Mbit/s. For transmission to the subscribers, the time division multiplex procedure (TDM) is used. For transmission in the opposite direction, a highly flexible time division multiple access procedure (TDMA) controls the access to PON for the subscriber-side line terminations. In order to keep the transmission system inexpensive emphasis is placed on a digital calibration of the fibre loop delay, a burst transmitter at the subscriber side without amplitude recovery and a burst receiver at the exchange side with purely digital bit synchronization. However, to achieve these features a small part of data rate must be used as a PON specific overhead.