Traffic Engineering for an Elastic Carrier-Concentrator System

This paper is one of three which describe a digital carrier-concentrator system with elastic traffic capacity. It deals with the traffic engineering considerations from a systems application viewpoint. One companion paper [1] describes the system organization, the switching function, supervision and control, and the reframing procedure. The other [2] describes the line equipment, delta codecs, line signaling functions, and an in-service line test facility. The system is unique in that the concentration switching function is nonblocking, but message channel quality varies with instantaneous traffic load. Realistic traffic limits are determined from consideration of message channel transmission degradations which may occur for small fractions of the busy hour. A suitable criterion is proposed, and the traffic capacity is calculated therefrom. The system provides telephone service to 256 subscriber lines over a singleT1digital line.     

Progress Towards Digital Subscriber Line Services and Signaling

With digital connectivity, future subscribers will be able to exercise local and network services involving the routine delivery, management, and processing of information. Accelerated by rapidly advancing technology, the evolutionary process towards digital connectivity and integrated voice and data services in the network is underway. This paper describes the methods of integrating voice and information capability into the telecommunications network. The attributes of this network will include the availability of digital connectivity directly to the subscriber, the availability of a robust signaling means between the subscriber and his local switching office, and common channel signaling to implement all interexchange signaling. Issues of interest include an overview of digital subscriber connectivity, signaling and information structures for these kinds of lines, communications protocols, and general network considerations for the provision of information services. Partitioning of intelligence between intelligent subscriber terminals and controllers and their switching system is investigated. The use of message and virtual channel switching facilities to handle limited information rate services is discussed. Finally, an exploratory digital subscriber line under investigation at Bell Laboratories is described.     

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.     

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.     

Integrated Digital Switching System with Queueing Storage Facility

This paper outlines the features of a new integrated switching system for voice and data. It is composed of integrated subscriber terminals, integrated subscriber lines, an integrated digital switching system, and integrated storage facilities. This paper shows that the introduction of the integrated storage facility can create various new service utilities and improve the traffic capacity of the system.     

A Single Channel Station Carrier System for Permanent Service Applications

The 84A station carrier system was designed to have cost and performance parameters competitive with paired cable for a majority of new subscriber loops. The system design incorporates a number of unique features, not provided by previous single channel systems, which are necessary for permanent service applications. These include: bridged ringing with ring-trip during ringing, central office power for the station terminal with disconnect during off-hook, dialing, or ringing on the physical channel, and transmission suppression of ringing signals below a set threshold. This paper describes the system and discusses the electrical design and the packaging concepts. Typical performance characteristics are listed.     

Subscriber Line Testing for Digital Switching Offices

This paper presents an overview of subscriber line testing as provided in Northern Telecom's Digital World^®family of host and remote digital switching systems. Capabilities provided in Digital World satisfy the major telco needs related to subscriber line testing. The various products incorporate interfaces to external test systems as well as internal line test facilities. A new subscriber line measurement technique is identified. It offers further advantages in speed and accuracy and has many potential applications in the analog and digital switching environments.     

Providing Multiple-Channel Communication Using the Experimental Digital Switch

This report describes the functional characteristics of a circuit-switched network which is capable of providing data communication paths as well as voice channels. In the system described, the circuit switch may be shared in order to provide multiple independently switched paths through the network. Unlike a conventional circuit switch, this sharing permits only a fraction of the switching capacity to be consumed which is proportional to the allocated bandwidth of the path. Additional economy is gained by providing multiple communication paths over the single communication resource between the subscriber and the switching machine. The fraction of the communication resource which is used by the subscriber is proportional to the total bandwidth of the channels which have been allocated. This allocation is performed dynamically, in response to subscriber requests. Algorithms are presented which perform this allocation efficiently. The resulting network provides a communication vehicle which provides both data and voice services in an integrated fashion.     

Control and Supervision of Remote Line Units

The ITT 1210 Class 5 digital switching system has a distributed control architecture with inherent remote line switching capability. A unique common channel signaling scheme permits control and supervision of these remote units. Testing and maintenance capabilities are, in general, identical and equivalent to those available in the 1210 host office. The Technical Assistance Center provides an extra overview level of backup maintenance for on-line assistance to personnel in any operational 1210 system.     

Distributed Microprocessors Control Architecture for Versatile Business Communications

This paper describes the NEAX®2400 Information Management System (IMS), which is no longer a conventional telephone switching system, but is instead a switching hub for various office automation equipment. The NEAX2400 IMS not only provides various circuit-switching functions such as conventional voice communication (telephone) switching, low-speed and high-speed data switching, but also provides stored and forward capabilities for voice (voice mail) and data (text mail, facsimile mail, etc.). This paper especially emphasizes the basic EPBX features and functions of the NEAX2400 IMS. The standard 64 kbit/s PCM technique is used for digitalization of voice signals, and switched through a nonblocking architecture time-division digital network. All digital data signals are transmitted through the same time-division digital network at the 64 kbit/s rate intermixed with digital voice signals. The controls of the switching functions, station service features, and maintenance service are performed by functionally divided distributed microprocessers. The most outstanding attribute of the NEAX2400 IMS is the unique building-block architecture of the equipment configuration. Modules are stacked above the basic module as the number of line and trunk ports, or additional stored and forward features are required. Up to four additional modules can be stacked up as a single module group. This unique arrangement permits the NEAX2400 IMS to be very flexible in its system applications and expandability. Practically, the NEAX2400 IMS will economically service as few as 184 ports (mixture of voice/data, line/trunk) and can be continuously expanded to as many as 23 184 ports.     

A conferencing technique for adaptive delta modulation

A technique for digital conferencing of voice signals in systems using adaptive delta modulation (ADM) with an idle pattern of alternating 1's and 0's has been described. Based on majority logic, it permits distortion-free reception of voice of a single active subscriber by all the other subscribers in the conference. Distortion exists when more than one subscriber is active and the extent of this distortion depends upon the type of ADM algorithm that has been used. An LSI oriented system based on time sharing of a common circuit by a number of channels has been implemented and tested. This technique, with only minor changes in circuitry, handles ADM channels that have idle patterns different from alternating single 1's and 0's.     

Jumbogroup Frequency Supply

The jumbogroup frequency supply provides the jumbogroup multiplex terminals with signals having the frequency accuracy(Delta F/F < 1/10^{8})required for frequency multiplexing 10 800 message channels. In addition to frequency precision, reliability is of utmost importance since many jumbogroup multiplex terminals are to be supplied by one jumbogroup frequency supply. Protection switching of redundant circuits and close monitoring of circuit conditions have been included in the design. Another major aspect of reliable operation is the man-machine interface, which has been engineered to minimize man-made service interruptions.     

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.     

A CMOS SLIC with an automatic balancing hybrid

A CMOS subscriber line interface circuit (SLIC) that has an automatic balancing hybrid facility is presented. Some of the key system aspects of line interface circuits, such as the relation between zero-loss switching and an automatic balancing hybrid circuit, power dissipation in the line circuit, and foreign voltage protection are described first. Next, details of the SLIC LSI, which comprises a dial pulse detecting circuit and and automatic balancing hybrid circuit, are described. The LSI is implemented with CMOS switched capacitor technology and is mounted on a 20-in DIL.     

Special ICs in digital switching-an overview

Traces the influence of special-purpose integrated and LSI circuits in digital switching systems. The existence of custom digital chips, codecs and filters, and high- and low-voltage analog cross-point arrays is related to the choice between alternative architectures. Recent trends toward replacing mature components such as transformers by subscriber line interface circuits (SLICs) are outlined.     

Delay and Throughput Evaluation of Switching Methods in Computer Communication Networks

Message, packet and line switching in computer communication networks are analyzed by a queueing model. Message transmission delay time and network throughput between a source-destination node pair are obtained as a function of various parameters including message length, traffic arriving at the network, and the number of switching nodes existing between the nodes. A criterion to determine the most suitable switching method under the given conditions is offered. Also, the maximum length of a packet in packet switching is discussed.     

Integrated electronic subscriber line interface circuit with ringing on chip

A new high-voltage, dielectrically isolated, complementary bipolar technology has been used to integrate high-voltage functions of a subscriber line interface circuit (SLIC). This circuit, in conjunction with a complementary low-voltage junction isolated bipolar integrated circuit, implements most of the line interface functions required for digital telephone switches. Partitioning of the junctions is based on technology requirements, and the two chips are encapsulated in 28-pin package.     

10 /spl Omega/ 370 V high voltage switches for line circuit application

The authors describe the integration of 8 high-voltage switches together with their low-voltage polygate CMOS control logic in an 18-pin package, the HVX chip. This custom IC is intended to be used as a switching cross-point between the subscriber line and circuit equipment in digital telephony. The high-voltage DMOS is processed in a dielectrically isolated substrate, and allows the switches to have both terminals floating with respect to the low-voltage circuitry. A novel control circuit guarantees that the switch status will be defined under all circumstances.     

Selection of Call Progress Tones for Digital Systems

The precise tone system based on the four basic frequencies 350, 440, 480, and 620 Hz is extensively used in switching systems to indicate readiness to dial, ringing of the called subscriber, lines or trunks busy, and other conditions. In digital switching systems it is normally advantageous to generate and process these tones in a digital form. It is shown that by judicious selection of the tone frequencies, considerable simplification of digital tone generators may be achieved. Modification of the precise tone frequencies within ± 0.5 percent reduces the number of samples which must be stored in ROM's from 1650 to 326. Another set of frequencies is given which requires only 228 samples and simplifies the tone generator readout logic.     

An Economic Analysis of Local Digital Time Division Exchange Networks

Digital time division switching may lead to important savings in local exchange areas experiencing high growth rates, digital trunk or subscriber carrier penetration and a large demand for special services. To capture these savings a wire center design with integrated pair gain and special services systems, as well as operational support systems, is postulated. Wire center savings are primarily the result of a reduction in the getting started cost of the assumed switch, a reduction in central office hardware with digital trunking and digital pair gain systems, a reduction in outside plant costs, a reduction in special service equipment through integration of switching and transmission treatment functions, a reduction in main distributing frame size and a reduction in operations expenses. These results are based on a "paper design" of a digital time division switch with projected cost profiles which may not be realizable in the near future.