Broadband Digital Networks Research Articles

Mutual clock synchronization in global digital communication networks

AbstractThere are numerous synchronization methodologies available for consideration in solving the problem of network synchronization in digital communication networks [1, 2]. They include: independent clocks, pulse stuffing, elastic stores, master‐slave hierarchical, time reference distribution, mutual synchronization, etc. This paper considers the network synchronization performance achievable using the method of mutual clock synchronization observed first by Christiaan Huygens in 1665 [3]. Network synchronization performance metrics studied include: nodal timing accuracy, timing jitter, slip rate, time interval between slips, probability of loss of synchronization. These metrics are shown to depend upon the distance (range) between clocks, ranging error, clock stability, nodal phase error processing bandwidth, data rate, signal‐to‐noise ratio and network connectivity. In this regard, the mutual synchronization performance achievable with long wavelength biological rhythms and electric power system rhythms is compared with the performance achievable using short wavelength rhythms required in wideband and broadband digital communications networks. The results are further applied to the problem of synchronizing a satellite communications network. When intrasatellite communication crosslinks (links between satellites in the same orbital plane) are used in a constellation of communication satellites, it is shown that the maximum data rate, the network connectivity and the constellation altitude drive the achievable network synchronization performance; the latter is set by technological limitations due to clock frequency stability, the maximum range between satellites and the minimum ranging error achievable by the ranging system. In this sense, low Earth orbits (LEO) are preferred over geosynchronous (GEO)Earth orbits. The theory is also applied to the Teledesic and Iridium networks.

Multilevel video coding and distribution architectures for emerging broadband digital networks

There is a renewed interest in video-based communications. The expected proliferation of various video communication applications has in turn resulted in a need for scalable and efficient digital video encoding schemes which would enable the dissemination of video signals at differing spatial resolution, depending on end-user needs and limitations. Also, along with this is the need for a universal broadband in which the same transmitted signal is efficiently distributed to various end-user applications, allowing them to communicate at differing grades of video quality. As a first step, this paper presents an efficient and scalable video coding scheme. The scheme is capable of encoding and decoding video signals in a hierarchical, multilayer fashion to provide video at differing quality grades, e.g., NTSC, extended quality (EQTV), high definition (HDTV). Since the lower levels in such a scheme can be encoded independently of the upper levels, compatibility with some of the standard codecs can be directly imposed. In addition, strategies to control quantization noise for independent transmission by means of residual layering are also discussed. This paper also discusses the utilization of this coding scheme to enable efficient bit rate sharing and robust distribution of video communication signals at three distinct quality grades in multicasting, as well as multipoint communication applications for multiparty video-conferencing. Two special distribution architectures are considered which involve the use of SMDS and ATM as the transport and delivery vehicles.

Privacy on the information superhighway: Will my house still be my castle?

Abstract With national policy and the convergence of telephone, cable, consumer electronic and computer technologies and industries, momentum has been established for the deployment of broadband digital interactive communications wide area network services and in-home information and automation functions aimed at the consumer. This new communication technology raises challenges to privacy, autonomy and democracy on an unprecedented scale. What is at stake and who are the stakeholders? What are the potential threats to society and to individual freedom? What are the proper limits of privacy for the consumer in the age of integrated digital electronic communication and how will such limits be established? Some fresh approaches are suggested.

The rupture process and aftershock distribution of the 6 April 1992 MS 6.8 earthquake, Offshore British Columbia

Abstract On 6 April 1992, a magnitude 6.8 (MS) earthquake occurred in the triple-junction region at the northern end of the Cascadia subduction zone. This was the largest earthquake in at least 75 yr to occur along the 110-km-long Revere-Dellwood-Wilson (RDW) transform fault and the first large earthquake in this region recorded by modern broadband digital seismic networks. It thus provides an opportunity to examine the rupture process along a young (<2 Ma) oceanic transform fault and to gain better insight into the tectonics of this triple-junction region. We have investigated the source parameters and the rupture process of this earthquake by modeling broadband body waves and long-period surface waves and by accurately locating the mainshock and the first 10 days of aftershocks using a well-located “calibration” event recorded during an ocean-bottom seismometer survey. Analysis of P and SH waveforms reveals that this was a complex rupture sequence consisting of three strike-slip subevents in 12 sec. The initial rupture occurred 5 to 6 km to the SW of the seafloor trace of the RDW fault at 50.55° N, 130.46° W. The dominant subevent occurred 2 to 3 sec later and 4.3 km beneath the seafloor trace of the RDW fault, and a third subevent occurred 5 sec later, 18 km to the NNW, suggesting a northwestward propagating rupture. The aftershock sequence extended along a 60- to 70-km-long segment of the RDW fault, with the bulk of the activity concentrated ∼30 to 40 km to the NNW of the epicenter, consistent with this interpretation. The well-constrained mechanism of the initial rupture (strike/dip/slip 339°/90°/−168°) and of the largest aftershock (165°/80°/170°) are rotated 15° to 20° clockwise relative to the seafloor trace of the RDW fault but are parallel to the Pacific/North America relative plate motion vector. In contrast, the mechanisms of the dominant subevent (326°/87°/−172°), and the long-period solution derived from surface waves aligns with the RDW fault. This suggests that small earthquakes (M < 6) in this area occur along faults that are optimally aligned with respect to the regional stress field, whereas large earthquakes, involving tens of kilometers of rupture, activate the RDW fault. For the mainshock, we estimate a seismic moment (from surface waves) of 1.0 × 1026 dyne-cm, a stress drop of 60 bars, and an average slip of 1.2 m. This represents only 21 yr of strain accumulation, implying that there is either a significant amount of aseismic slip along the RDW fault or that much of the strain accumulation manifests itself as deformation within the Dellwood and Winona blocks or along the continental margin.

Configuring express pipes in emerging telecommunication networks

Over the past few decades, telecommunication networks have been designed and implemented to support a wide variety of services, including the integration of a customer's voice, data and video communication requirements. Rapid advances in VLSI technology, coupled with declining costs of fiber-based transmission systems, have resulted in high speed, broadband digital networks capable of transporting hundreds of megabits per second. At the same time, a growing number of business customers have expressed the need for controlling and re-configuring their private networks themselves, to better match their business needs. In digital networks, a key component in allowing this flexibility is the establishment of intelligent Digital Cross-Connect Systems (DCS). With DCS, network re-configuration, including bandwidth allocation and topology changes, can be made on a near real time basis, or be scheduled on a reservation basis to take place once (or multiple times) in the future. In this paper, we study the application of digital cross-connect systems in packet switched networks. These systems allow the designer to configure express pipes or direct links between source--destination pairs that have high communication traffic requirements. Since express pipes are configured by borrowing channels from the underlying, leased, backbone network, establishing a direct link reduces the number of "free" channels available for regular switched traffic, and consequently have the potential of increasing queueing delays. We formulate the problem of judiciously selecting express pipes as a 0/1 nonlinear integer programming problem, that seeks to minimize overall network delay. An efficient Lagrangian relaxation based solution procedure is proposed. Results of computational experiments with the proposed solution technique are also reported.

Teletraffic issues in ATM networks

In recent years we have witnessed a rapid development of broadband digital communication technology, driven by the maturity of fiber-optic transmission techniques. Fiber-optic lines capable of transmitting data at a speed from 45 up to 155 megabits per second (Mbps) are already operational. In addition, transmission speeds as high as 3.4 gigabits per second (Gbps) have been achieved in research labs. Compared to the conventional Tl-speed (1.544 Mbps) network, a broadband fiber-optic network can serve not only the conventional data communication demands, but also provide sufficient bandwidth to facilitate new applications, such as voice and video. In today's telecommunication networks, however, traffic from these applications are still carried by separate, dedicated networks, e.g., the traditional telephony for voice, and cable TV for motion pictures. Work is currently being conducted by many organizations to explore the possibilities of integrating diverse communication demands (data, voice, and video) over a common broadband digital network covering a wide area,

Combining DCT and subband coding into an intraframe coder

The advent of broadband digital networks will make it possible to transmit high quality digital television. Subband coding is a very interesting coding scheme as it accommodates a transmission quality that can flexibly adapt to the available channel capacity. Subband coding (SBC) and block cosine-transform techniques have already been used together, but only to code the low-pass image. Residual spatial correlation present in higher frequencies bands has only partially been taken care of. This paper presents the results obtained with a simulated coder in which DCT is used in all bands where expected spatial correlation is high enough. The use of a pyramid vector quantizer is proposed. Results are good and compare favourably with other results published in the literature.

Simultaneous optical amplification, detection, and transmission using in-line semiconductor laser amplifiers

It is demonstrated that in broadband networks inline semiconductor laser amplifiers (SLAs) that provide system gain can also be used as simultaneous transceivers for additional channels at higher frequencies. In the experiment, an SLA in a 622-Mb/s baseband system provided a 6.5-dB fiber-to-fiber gain and served simultaneously as a receiver and a transmitter for two frequency-shift-keying (FSK) channels (each carrying 10 Mb/s) at 755 and 1075 MHz, respectively. Such optical amplifiers/transceivers are potentially useful in broadband digital networks with out-of-band signaling channels or in subcarrier multiple-access networks.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Telecommunications and Spatial Restructuring: An Australian Perpective

Changes over the past twenty-five years in information and communication technology (ICT) are beginning to provide us with a clearer picture of the technical platform that will influence the shape of urban and industrial development into the 21st century. During this period we have experienced a number of key paradigm shifts in computing: from 1960s batch systems to 1970s time sharing systems to 1980s desktop systems (Newton et al. 1988). At the same time, but somewhat independently, communications were evolving from the slow speed analogue public switched telephone network which provided a measure of computer-to-computer interaction (via modems) to the newly emerging high speed broadband digital networks, networks which will provide a truly vast array of value added products and services (discussed more fully in Cavill and Fidler' paper). The dramatic price-performance improvements in these technologies and the synergy which now exists between computers and communications provides us in the 1990s with th...

Hospital-wide distribution of nuclear medicine studies through a broadband digital network

Nuclear medicine provides a good environment for the evaluation of picture archiving and communication systems (PACS) because of the relatively small quantity of digital data that are generated, leading to reduced requirements for storage, display, and transmission compared with those found in radiology. The PACS in nuclear medicine is characterized by use of a single computer as a central storage, display, and analysis node. Images are acquired with use of small, low-cost computers attached to each camera. This network configuration offers advantages of convenience, but with great reliance on a single computer. A campus-wide picture network is under development at Washington University employing broadband cable television technology supplemented by baseband Ethernet (Digital Equipment Corp, Maynard, MA) components. All areas of diagnostic radiology and nuclear medicine are connected via a PACS testbed project. A radiology information system, supporting over 250 terminals, provides digital tracking of patients and report generation and retrieval. A new image workstation is under development in conjunction with Digital Equipment Corp. This system will permit display in multiple windows of report information and images from various modalities. A lung scan demonstration project is now beginning that is designed to test the value of a PACS in nuclear medicine. Digitally acquired chest radiographs will be displayed on an image workstation in nuclear medicine along with digital ventilation and perfusion lung scans. It is hoped that time-consuming logistic bottlenecks now encountered in lung scan interpretation will be reduced.

United States National seismograph network

The USGS National Earthquake Information Center (NEIC) has planned and is developing a broadband digital seismograph network for the United States. The network will consist of approximately 150 seismograph stations distributed across the contiguous 48 states and across Alaska, Hawaii, Puerto Rico and the Virgin Islands. Data transmission will be via two-way satellite telemetry from the network sites to a central recording facility at the NEIC in Golden, Colorado. The design goal for the network is the on-scale recording by at least five well-distributed stations of any seismic event of magnitude 2.5 or greater in all areas of the United States except possibly part of Alaska. All event data from the network will be distributed to the scientific community on compact disc with read-only memory (CD-ROM).

Visual Communications And Image Processing

This special issue on Visual Communications and Image Processing contains 14 papers that cover a wide spectrum in this fast growing area. For the past few decades, researchers and scientists have devoted their efforts to these fields. Through this long-lasting devotion, we witness today the growing popularity of low-bit-rate video as a convenient tool for visual communication. We also see the integration of high-quality video into broadband digital networks. Today, with more sophisticated processing, clearer and sharper pictures are being restored from blurring and noise. Also, thanks to the advances in digital image processing, even a PC-based system can be built to recognize highly complicated Chinese characters at the speed of 300 characters per minute. This special issue can be viewed as a milestone of visual communications and image processing on its journey to eternity. It presents some overviews on advanced topics as well as some new development in specific subjects.