Subscriber Carrier Systems Research Articles

D4 Digital Channel Bank Family: TheSLC™-96 System

The SLC∗-96 system is a digital subscriber carrier system that can carry up to 96 subscriber channels, when fully equipped, between a Central Office Terminal (COT) and a Remote Terminal (RT), using T1 digital lines. Typical economic applications are for expanding the service capability of existing cable plant or for new wire center deferral. Recent application studies show that SLC-96 systems will be economically attractive in many permanent subscriber applications. In addition to Message Telephone Service (MTS), the system can provide coin services, voice-frequency special services, and digital data services. The SLC-96 system is based on the transmission and physical format of the D4 system used for interoffice trunks. The system employs μ255 pulse code modulation (PCM) for voice transmission and, as a result, will allow the direct interface of the RT with a digital central office. Its maintenance features include channel and drop testing from a local test desk; single-ended, active, T1 fault-locating; automatic T1 line protection; extensive local and remote alarm displays; and outputs that can be transmitted to a remote operations center such as the Switching Control Center (SCC). The channel and drop testing scheme requires a Pair Gain Test Controller (PGTC) to be installed in each wire center containing one or more SLC-96 systems. Various other features that will enhance the application of the SLC-96 system in the loop plant include extended range channel units, remote T1 line power feed, and a variety of RT enclosures.

A Digital Subscriber Carrier System for the Evolving Subscriber Loop Network

Subscriber carrier systems such as DMS-1(TM)are currently being widely used for rural outside plant relief applications. However, there is a much larger application base for subscriber carrier in urban areas. Urban carrier systems will require significantly different features compared with rural systems. The applicability of these systems in urban loop plant is discussed and a system being designed by Northern Telecom and Bell-Northern Research to complement the existing DMS-1 system is described.

Modem chip for subscriber carrier system

This paper is focused on the design and realization of a custom IC applied as the backbone of a subscriber carrier system. The chip contains both a modulator and demodulator, and is realized on a small die size in a standard low voltage bipolar technology. The carrier system architecture is such that, for both the exchange and the subscriber modem, the same IC can be used with a minimum of external components. Specifically interesting on the IC itself is the overall DC coupling in order to reduce the number of output pins and external components, the biasing and powering scheme which results in a very low power dissipation (mandatory for line-charged battery operation), the wide range of automatic gain control, and the precautions taken to prevent carrier intermodulation.

A Digital Concentrator for the SLC™-96 System

The SLC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sup> -96 subscriber loop carrier system is a digital subscriber carrier system serving up to 96 single-party customers. The system can be configured with an optional plug-in which digitally concentrates two standard, 1.544 megabit, serial pulse-code modulation (PCM) bit streams into a single stream, thereby concentrating 48 customers onto a single T1 digital line. The concentrator employs a custom NMOS lsi chip providing a full-access, time-slot interchange function. It has microcomputer controllers at the two ends of the system to control time-slot assignments. The development of the concentrator involved challenges in chip design, software design, and performance testing.

Guest Editor's Prologue: The Thrust of Electronic Systems in the Subscriber Loop Plant

In the closing years of the 1970s, two complementary technological trends emerged which are on the verge of bringing the electronic loop network to fruition as the prescription of choice for growth in the suburban and urban loop plant: highly integrated digital telecommunications networks, and intelligent electronic systems. Digital subscriber carrier systems, experiencing significant cost reductions from dramatic advances in digital LSI technology, were introduced in the mid 1970s, and by 1979 were functionally integrated with new local digital switches. At the same time, the economics of digital carrier were challenged by emerging intelligent electronic range-extender systems which provided automatic voice and signaling gain as well as increasingly lower per-channel cost. Integrated with large stored-program-control analog switches, such range extenders could be concentrated behind the first stages of switching and automatically adjust themselves to provide optimal transmission treatment to whatever subscriber they served based on measurements made instantaneously at time of call setup. Both of these approaches to lower cost loop systems are being complemented by increasingly intelligent automatic maintenance diagnostic systems which enhance their value to the operating companies. It is from this vantage point that the first paper in this special section unveils the scenario for the continued development of the electronic loop network. In considerable detail, the next three papers reveal the latest integrated range extension system plan based on intelligent interaction with the host office and customer plant and its implementation in the Bell System. The final three papers - from Japan, France, and Canada - project into the future and examine the strategies by which advanced digital technology and fiber optic facilities will be merged with operating system overlays to provide new telecommunication services that promise to provide customer services and conveniences undreamed of but 15 years before.

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.

Expected Crosstalk Performance of Analog Multichannel Subscriber Carrier Systems

This paper determines the intelligible crosstalk performance of analog multichannel subscriber carrier systems. Using a 0.1 percent probability of intelligible crosstalk objective, the calculations determine that the equal level far-end crosstalk loss must exceed 55.6 dB. Based on crosstalk measurements of in-service cables in South Central Bell, it is shown that only a small fraction of the pairs fail the crosstalk objective. Hence, it is concluded that multichannel analog subscriber carrier systems can be applied without any cable crosstalk constraints.

Carrier Transmission on Voice Loaded Loops

A new telephone line loading scheme is reported that permits application of subscriber carrier systems to voice loaded cable pairs with practically no degradation to either voice or carrier transmission. This scheme, termed super-loading, makes use of a bifilar wound toroidal inductor having both windings center tapped, with an LC network joining the center taps. This arrangement produces a device that acts as a one-to-one transformer at frequencies where the LC network presents a low impedance and a series inductor when the network impedance is high. Data are presented comparing the transmission characteristics of nonloaded, nominally loaded, and super-loaded cable pairs at voice and carrier frequencies.

Subscriber Loop Plant of Rural Telephone Systems

The subscriber loop plant of rural telephone systems is described on the basis of a nationwide sampling survey of the subscriber circuits of the REA telephone borrowers. The sample consists of 1000 main telephones drawn randomly from a universe of 1 375 000 main telephones under a statistical sampling plan. The survey provided a complete description of the plant serving each of the sampled telephones. By computer analysis of the data, patterns of plant composition, average costs, and distribution of subscribers in terms of distance from the serving central office are developed. The construction cost advantage of buried plant is stressed by showing how greatly pole lines (poles, crossarms, guys, etc.) contribute to the cost of serving rural subscribers by means of aerial plant. Guidelines are given for a plant improvement program to correct deviations from current standard design revealed by the survey data. The importance of the data for use in evaluating techniques for upgrading and establishing cost parameters for proposed subscriber carrier systems is indicated.

Engineering features and field trial performance of a new subscriber carrier system

IN LATE WINTER of 1956, Stromberg-Carlson Company placed a new-subscriber carrier system, known as 561 carrier, on field trial operation. This system is a result of approximately 15 months of intensive effort by many people in a number of specialized fields of engineering. System layout, circuitry, filters, packaging, printed circuitry, and components all required much basic engineering to achieve the results finally obtained in this system.

A new 5-channel carrier system for subscriber use employing transistors

THE NEW Subscriber-Carrier System type 561 described in this paper is a result of many months of engineering effort by many individuals in the Stromberg-Carlson organization. The design was undertaken to satisfy a pressing need in the telephone industry for an inexpensive yet good quality system which would help alleviate the critical situation existing in the field of rural service.