Showing papers in "IEEE Communications Magazine in 1988"

The QPSX MAN

Abstract: The authors discuss QPSX (queued packet and synchronous switch), a distributed switch/network that will fulfil the requirements of a public metropolitan area network (MAN) and has wide telephone industry support. The dual-bus architecture of QPSX and its extension, the looped-bus architecture, are described. The architecture of the public MAN is examined, particularly with respect to QPSX as a proposal for IEE P802.6 standardization. The distributed queueing protocol, segmentation and reassembly scheme, and reliability features of the QPSX network are discussed. >

G.722: a new CCITT coding standard for digital transmission of wideband audio signals

Abstract: CCITT Study Group XVIII recognized the need for a new international coding standard on high-quality audio to allow interconnection of diverse switching, transmission, and terminal equipment and organized an expert group in 1983 to recommend an appropriate coding technique. A tutorial discussion is provided of the adaptive differential PCM (pulse-code modulation) coding method recommended by the group. The discussion covers the subjective performance tests performed, mode initialization and mode switching, data-speed multiplexing, and communication between narrowband and wideband terminals. >

Standards for metropolitan area networks

Abstract: The differences between local area networks (LANs) and metropolitan area networks (MANs) are outlined, and their impact on MAN standards is explored. The discussion covers IEEE P802's view of metropolitan area networks, MAN architecture, early proposals considered by the IEEE 802.6 committee, fiber optic proposals, and the emerging consensus. The need for field experience and the anticipated timetable for the IEEE P802.6 standard are also examined. >

Differential operation of the Global Positioning System

Abstract: The principles of differential operation of the Global Positioning System (DGPS) are discussed. DGPS error sources and their influence on spatial and temporal correlation are analyzed. The standards for the differential corrections and the auxiliary messages which have been developed by the Radio Technical Commission for Maritime Services are then described. The dependence of DGPS accuracy on satellite geometry is examined. Two possible DGPS data links are described, and the applications, advantages, and limitations of each are discussed. The first data link would use the extant marine radiobeacon network (a medium-frequency system) and provide coastal coverage. The second data link would use pseudosatellites and provide additional lines of position as well as carry the differential correction. >

Multi-media information services: a laboratory study

Abstract: An overview is given of the work of a research group studying advanced information services. The general form of today's information services is discussed as a baseline for considering the future, and some key technological advances (including a broadband public-switched network) that are expected to greatly influence the continuing evolution of such services are listed. A description is given of a multimedia information services laboratory, consisting of a services testbed and application prototypes, which was constructed to illustrate and study important aspects of future services. The end-to-end performance requirements for these services are examined. Two examples are given to illustrate universal communications. >

Shared workspaces for group collaboration: an experiment using Internet and UNIX interprocess communications

Abstract: The system described is intended to link institutions (such as universities or industrial research organizations) that have most of their computers connected to local area networks (LANs). The main objective of the research is to bring users of remote systems together to collaborate in reviewing and editing documents containing text, graphs and image objects. The term workspace is used to denote a collection of such objects belonging to some application, and the software tools needed to access these objects. The major components of the system and the user interface are presented. A prototype implemented in C under 4.3BSD UNIX is discussed. The system is then related to and contrasted with other work on group collaboration. The suitability and shortcomings of UNIX as an operating system for building group collaboration software tools are assessed. >

A symptom-driven expert system for isolating and correcting network faults

Abstract: A description is given of Troubleshooter, a system for diagnosing problems in the Datakit Virtual Circuit Switch networking environment. This system is representative of applications using expert systems as diagnostic tools. Troubleshooter uses software tools from the academic laboratories, most notably OP24 from Carnegie-Mellon University and Franz LISP from the University of California at Berkeley. Extensive laboratory tests has confirmed Troubleshooter's ability to detect faults. >

Switched multi-megabit data service and early availability via MAN technology

Abstract: The authors discuss work currently proceeding at Bell Communications Research in the field of novel high-speed data services and supporting network requirements. The service described herein, switched multimegabit data service (SMDS), is one that could be offered by carrier networks to meet emerging customer high-speed data needs. The authors provide an overview of the motivations behind the service development and discuss the importance of the embedded customer base and the factors that significantly influence the nature of the service. They then describe specific SMDS features and characteristics and the use of MAN technology for the support of SMDS. >

Quality assessments for visual service

Abstract: Three kinds of visual services, namely highly band-compressed, conventional, and high definition, are considered. Evaluation in terms of factors basic to all three classes are considered. The picture quality scale (PQS) is discussed, and its use in assessing color image coding and coder design is examined. Deterioration of moving images due to blur and to field or frame repetition is addressed. The problems relevant to high-definition visual services are described. >

Integrated voice/data switching

Abstract: A basic understanding of the technical problems in integrating voice and data is provided. The different types of traffic found in communication systems are examined. Integration is investigated at different levels. In particular, the focus is on the integration of voice and data at the switching level. Different switching approaches are compared and some integrated-switching systems are described. >

VSAT communications networks-an overview

Abstract: The very-small-aperture-terminal (VSAT) fixed satellite communication network is a star network in which many dispersed micro terminals attempt to send data in a packet form through a random access/time-division multiple-access (RA/TDMA) satellite channel with transmission delay. The basic concept of the VSAT and its service potential are discussed. Two classes of traffic are addressed, namely business-oriented low-rate-data traffic and bulk data traffic of corporate networks. Satellite access, throughput, and delay are considered. The size of the network population that can be served in an RA/TDMA environment is calculated. User protocols are examined. A typical VSAT business scenario is described. >

Methods of addressing the interactions of intelligent network services with embedded switch services

Abstract: A key factor in the transition of the existing network to an intelligent network (IN) environment is the need to partition the network intelligence and to ensure the coexistence of the embedded switch services with the externally controlled services. If the network intelligence can be defined by entities (e.g. access control and routing, connection control, basic call control, feature control, etc.), then the issue is how to manage their distribution over the evolving network elements (NEs). The authors focus on the early phases of the IN, during a 1991-2 time frame, when these features must interwork with the existing features (e.g. those within the Centrex service). They provide an overview of the features interactions and arbitration policies prevailing in today's network. They then describe the framework for both single- and multinode networked features models. The issues of call control distributed over the NEs of the IN are treated as extensions to the concepts and interfaces needed to provide networked services like areawide Centrex and private virtual networks. A model for offering IN/1+ services is described. >

The intelligent network and forward-looking technology

Abstract: The authors discuss the Advanced Intelligent Network (AIN), an architecture that includes both IN/1+ and IN/2 and will be introduced in phases, with releases envisioned at two-year intervals. Phase 1 requirements will be released in 1989 and first applications are targeted for deployment in 1991/2. They examine some future technologies and their impact on the AIN. They describe an AIN system architecture that can respond to change, concentrating on the effect of switching-system evolution to narrowband and broadband ISDN. >

Quality assessment of speech coding and speech synthesis systems

Abstract: The concept of speech quality assessment is examined. Quality assessment methodologies for speech waveform coding, source coding, and speech synthesis by rule from the viewpoints of naturalness and intelligibility are reviewed. Both subjective and objective measures are considered. >

Alternative local area network access protocols

Abstract: The course of recent research is outlined, and state-of-the-art protocols are surveyed. The various classes of access protocols and corresponding performance models are covered. These are fixed assignment access, random-assignment access, demand assignment access, integrated local area networks, and multichannel local area networks. >

A framework for defining the quality of communications services

Abstract: A framework is described that was developed to help assess communications service quality in a manner that most closely reflects the broad array of performance parameters experienced by customers. Examples of its application are presented. An additional benefit experienced with the use of this framework is a more consistent, disciplined analysis of service parameters, adding to the thoroughness with which service providers and customers alike assess the quality of communications services. >

Channel access protocols for Ku-band VSAT networks: a comparative evaluation

Abstract: The performance of candidate protocols for first-generation Ku-band very small aperture terminal (VSAT) satellite networks is compared. The goal is to assist the process of selecting a protocol. The performance comparison is carried out over a range of possible traffic, channel and satellite parameters, leading to an understanding of the appropriate regime for each of the protocols under consideration. The protocols considered are unslotted Aloha, slotted Aloha, selective-reject (SRE) Aloha, and demand-assigned time-division multiple-access (TDMA) or DAMA. >

Designing service-independent capabilities for intelligent networks

Abstract: A key attribute desired of intelligent networks is the ability to design multiple services from a set of service-independent capabilities. Some aspects of the planning, requirements specification, design. and development processes to produce such capabilities are examined. Important factors and considerations necessary to the successful realization of service independence are described. >

Future optical fiber transmission technology and networks

Abstract: The authors contend that optical system developments, which so far have followed a straightforward and logical path from direct link replacement to the proposed transwitching networks, will evolve towards passive (fiber-only) networks that could ultimately see the eradication of the central office. To explain this view of the future, they briefly trace optical system developments to the present day before citing the technology developments that have led them to the conclusion. They discuss present network and technology trends, focusing on the reduction of the amount of electronic hardware, the disappearance of bandwidth efficiency as an important factor, and the state of the optical network today. They then turn to the future network and technology, showing how the central office can be dispensed with by operating the network on a radio mode, with each terminal assigned a specific frequency. >

Diversity protections for digital radio-summary of ten-year experiments and studies

Abstract: A summary is presented of a series of critical experiments that led to recent discoveries of large improvement factors for digital radio performance by antenna pattern diversity, antenna angle diversity, frequency diversity, and space diversity. The measured diversity improvement factors for digital radio against multipath dispersive fading are larger than those predicted by the existing analog radio model by at least one order of magnitude. Applications of these findings will lead to substantial savings in the cost for diversity protections for digital radio routes. These discoveries stimulated the development of new models of diversity improvement factors for digital radio and the development of the DRDIV computer program for engineering digital radio routes. Background information is given on multipath fading and diversity concepts, and a glossary of terms is included. >

Advanced satellite concepts for future generation VSAT networks

Abstract: Advanced communication networks that use very-small-aperture terminals (VSATs) are considered. The techniques and technologies suitable for powerful satellites and system architectures for future VSAT networks are discussed. These include high effective isotropic radiated power, multiple-beam satellite antennas, and various access techniques. Examples of systems planned by the government and private industry are described. >

Toroidal networks

Abstract: The essential features of the toroidal network topology are examined, and its performance is evaluated. Some of the proposed applications of toroidal networks are described. Included in the discussion are metropolitan area network communication and multiprocessor interconnection, as well as the use of VLSI technology. >

Voice-band data communication modems - A historical review: 1919-1988

Abstract: The history of voice-band data modems is divided into four periods, and the activities in each of these eras is discussed. Before the early 1950s, work was done on quantitatively measuring phase distortion and equalizing lines with such distortion. The advent of the digital computer in the early 1950s and the resulting military and commercial interest in large-scale data processing systems led to interest in using telephone lines for transmitting digital information. The research efforts during this period and the resulting commercial products are described. The third era, during the 1970s was characterized by extensive research and technology advances. The discussion focuses on advances in timing recovery, adaptive filtering, semiconductor technology and modem design, and pulse-shaping filters. The late 1970s and early 1980s have seen the development of ultrahigh-speed modems. Coding for performance improvement and the development of 19.2 kb/s modems in this period are discussed. >

VSAT networks: architectures, protocols, and management

Abstract: VSAT (very-small-aperture terminal) satellite networks, are discussed, focusing on a particular network called STARCOM. The STARCOM system architecture is presented. A multiple-access protocol developed specifically for the STARCOM system is described and its performance is examined. The management capabilities of the STARCOM system are considered in detail. >

Integrated voice and data communications overview

Abstract: The author reviews architectures and traffic characteristics for voice and data communications, and addresses important issues in integrated voice and data communications. He discusses some possible methods of integrating voice and data and presents an example of implementing integrated voice and data communications. He considers ISDN (integrated services digital network) as a vehicle for supporting integrated services including voice and data as well as image and video. Although the concern is mainly with switched networks, some of the concepts discussed are applicable to both switched and special-services networks. >

Packet forwarding

Abstract: A packet network is viewed as consisting of two major interacting layers: a lower layer responsible for the determination of a set of paths that can be used to carry packet flows, and an upper layer responsible for actually sending the flows over these paths, on a per-packet basis. A systematic review is provided of the various techniques that can be used to perform the actual packet-by-packet routing operation at the upper layer, called the packet forwarding function. The function components of a routing system and its characteristics (responsiveness to changes in network state and degree of centralization) are discussed. Five routing techniques are then examined, namely source, directory, destination, global-path, and channel-link-path routing. >

Intelligent network/2: The architecture-The technical challenges-The opportunities

Abstract: The Intelligent Network/2 (IN/2) architecture concept diverges from the traditional new service introduction approach by distributing call-processing capabilities across multiple network modules, by constructing network services with service-independent capabilities, and by using standard signaling protocols among the network elements. The IN/2 approach provides opportunities to implement new services while reducing the service introduction interval. The IN/1 architecture provides new-service introduction from a centralized point, allowing users throughout a wide geographic area to have access to the service simultaneously. The IN/2 concept extends the IN/1 approach and sharply reduces the new-service introduction interval. IN/2 applies the premise that multiple network services or service features can be constructed from a set of reusable network capabilities, which apply to many services and are therefore independent of a particular service application. An overview of the IN/2 architecture is presented, highlighting the key technical issues. >

Advanced coherent lightwave technologies

Abstract: The present state of optical coherent communication technologies, covering optical heterodyne/homodyne detection and optical frequency division multiplexing (optimal FDM), is discussed. Included is a description of the development history of coherent lightwave communication technology followed by a discussion of heterodyne detection for future long-haul high-speed systems. A description of optical coherent transmission systems using heterodyne/homodyne detection is presented along with a review of optical FDM technology and its applications. Future trends are examined. >

Emerging technology and service enhancement for cordless telephone systems

Abstract: A brief history of the development of cordless telephone systems in Japan is given. The efficient frequency utilization and upgraded service provided by this technology are discussed. A business cordless system is proposed for extended service areas using a portable telephone facility. The potential extension of this system to a local area portable telephone system is mentioned. >

Nonlinear phenomena in optical fibers

Abstract: April 1988-Vol. 26, No. 4 IEEE Communications Magazine 36 he invention o f the laser stimul;ited \,arious T researchers t o the realization that the w r y high optical intensities achievahlc i n focused laser beams \vould make it possihlc t o study, and perhaps exploit, the nonlinear optical rcsponscs of materials. I t hacl long been rccognired that the optical properties of most n~ateri:ils (i.e., their refracti\.r index and absorpt ion) depend on ttie optical intensity, but Ivith nonlaser sources these effects could in general br detcctecl 0111). in very sensitive rxperirnents. T h e availability of tiigli-jxnvcipulsed lasers has, itidrecl, macle nonlinear opt i ts a 1w-y acti\re, diverse, and productive field of r c sea rc h . Ih e a va i 1 ab i 1 i t y of 1 ow 1 o s s si II g 1 c rnoclr opt i cal fihcrs has no\v made it possible to ohservc nonlitirar optical phenomena a t substantially lower intensity le\.el$, and has stimulated interest in t\vo complcinentary quc5tions. To what extent can nonlinear optical effects be exploited to enhance the capabilities o f fiber coinni 11 n ica t ion s systems? '1.0 w ha t ex ten t \v i 1 1 t i on 1 i nea r (1 p t i ca 1 ph e n oinc na 1 i in i t t he U 1 t i in ii t c cii pa b i 1 i ties of opt i ca 1 f i 1)cr coni m u n ica ti o n s s y s tr m s! I II t h is art ic 1 c tvr t-eI,iew some of the ciirrent ansivers t o these and related questions. ~I 'he key charactc~istic o f optical fibers that makes i t possible to observe n o n l i n e x effect5 with relatively modest p o u ~ ~ s is that , a s the light is guided along ..I libet-, the effects o f t i smal l changes in its optical pmperties can a d c l u p over interaction lengths of m a n y meters, 01r\.en kilometers. By contrast, when ;I frrel>pinpagat ing beam is focused t o thc size o f ;I typical single-mode tiher core i t \vi11 then spread quitt. t-;ipidy (because of diffraction), at id the cffcctiw interac t i o i i Iciigth achievable is -100 pin o r less. Ewri Lvith the long interat tion Irngths ;ichirv:il)lc in lil)ers, the nonlinearit) ot fusrd silic-Li (thv mijot (oiistituciit of mo?t (ornmLinications fibers) is sufficiently smal l that i t d o c s r i o t produce ;I rioticcal)lc effect a t the ponw l c ~ ~ l s ( . t i m m t 1 ). U s c d i 11 coin rri uii ica t ions s y s tciiis. For ( ~ x a I 11 pk, ;in o p t i c a1 poiver of I m F V in ;I typic.al single-mode fiber gi\.cs a n intensity o f -2 kFV cti i ' , lvhic t i \vi11 in( rwse the 1-eft-acti1.c irides of thr fiber (ore' h y -6 X 10I . Even 101a n effective i n r r i x tion Iength of I O kri.,, \v t i i ( ti is abut IO"' \vavclengths, this is still ;I ticgligil ) l ~ siii;ill effc~ct. H o ~ v e v c i ~ , some ot t h e , tibet. systems c u i tenrly under study i n v o l ~ ~ multiplexing ;IS many as ;I IiiindIed oi more intlrpeiidrtit ( hani ic~ls 011 21 singlr fi1)c.r. Lvliic ti ( a i 1 result in signific:tritly Iiigliri penvet' Ivvvls in thr fihei-, ;incl opms thv possihilit). ot ititrractions h e t n ~ ~ w thtl signals. I n ;itldition, systems usiiig c~ohrrcvit dctec-tion m e Iikel! to lx, cmiisitlerahly inow sc'risiti\,c to rhc c,ffec I S of nonl inc~at~i~ ics than ttie pre5,ctit dire( t-detcctioti systrms. 12'hilc the riotiliricarirics of fused silica t i h m ai.e siiffic icntl! srnall that they have not i t i ip ; i ( trtl the pic+ crit ti1)c.i. sFstenis, they arc srtfficientl) large t h a r fibeihas l)c( onie ;I referred medium for invc~stigations cl1 t i o I 11 i i i c , ; ~ r 01) t ic-a 1 phc tionicna . Th i s h a s res U 1 t ed i 11 the dcvc~lopnici i t of se\cral nonliiiear optical cle\.ic.es iisinq fi1)ct.s. \vhic.h ha\.c, iippli( atioris in the de\.t~lopmrrit ( : i f