Bursty Nature Research Articles

Modeling and analysis of a tandem link connection under the burst-error condition

Transmission errors are known to be bursty in nature. In block-oriented data communication, this bursty error behavior should be treated assuming that there are non-renewal correlations between the transmission conditions of data block. In this paper, using the stochastic sequential machine method the authors suggest a block-level burst error model of a digital tandem connection that consists of a set of segmented channels, and then investigate several end-to-end error performance characteristics under the burst-error condition. Also, they derive expressions that approximate the tandem connection model parameters by combining individual segment channel models into an equivalent combined error model. They show the proposed method is very useful in describing the error performance of tandem link connections.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Capacity of a cellular time division duplex CDMA system

A time division duplex (TDD) technique is considered for a CDMA cellular system. Its use enables all the multipath combining (using a RAKE type receiver) to be located in the base site rather than in the mobile unit. This is possible due to the reciprocal uplink and downlink channels which are created by time division, and employ the same carrier frequency. Simulations show that at low Doppler fading rates TDD is only marginally lower in cell capacity than conventional frequency division duplex (FDD) techniques. However, at higher Doppler fading rates (for high speed mobiles) the cell capacity degrades in a nonlinear manner and will breakdown suddenly, unlike that of a comparable FDD CDMA system. The limitation of the TDD technique results from the noncontinuous receiver training caused by the bursty nature of the communications. Losses in cell capacity are also due to the guard times inserted between the uplink and downlink transmissions.

Plasma flow bursts in the nightside auroral zone ionosphere and their relation to geomagnetic activity

We examine the nature of flows in the nightside auroral zone ionosphere and their relationship with concurrent geomagnetic activity by studying a three-hour interval of ground-based radar, magnetometer array and spacecraft data. We find that the flows are bursty in nature, a characteristic previously reported, and that the bursts are related to a series of substorm electrojet intensifications initiated in the pre-midnight sector.

Analysis of packet loss processes in high-speed networks

The packet loss process in a single-server queueing system with a finite buffer capacity is analyzed. The model used addresses the packet loss probabilities for packets within a block of a consecutive sequence of packets. An analytical approach is presented that yields efficient recursions for the computation of the distribution of the number of lost packets within a block of packets of fixed or variable size for several arrival models and several numbers of sessions. Numerical examples are provided to compare the distribution obtained with that obtained using the independence assumption to compute the loss probabilities of packets within a block. The results show that forward error correction schemes become less efficient due to the bursty nature of the packet loss processes; real-time traffic might be more sensitive to network congestion than was previously assumed; and the retransmission probability of ATM messages has been overestimated by the use of the independence assumption.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evaluation of end‐to‐end performance for data traffic in ATM networks

AbstractWhen data traffic communications are serviced in ATM networks, a packet from the transmission source is divided into cells to be transmitted. Therefore, the assumption of the Poisson arrival of data packets used widely in the past is unreasonable and the bursty nature of data traffic must be considered. Furthermore, the end‐to‐end packet loss rate rather than the cell loss rate becomes more important in data traffic and retransmission due to packet loss must be considered in evaluating the packet transmission delay.In this paper, communications of data traffic in an ATM environment are considered by analyzing transmission of data traffic over a number of switching machines using a queueing network model allowing performance characteristics such as the end‐to‐end packet loss rate and the average delay of data traffic.

Dynamic dependency analysis of ordinary programs

A quantitative analysis of program execution is essential to the computer architecture design process. With the current trend in architecture of enhancing the performance of uniprocessors by exploiting fine-grain parallelism, first-order metrics of program execution, such as operation frequencies, are not sufficient; characterizing the exact nature of dependencies between operations is essential. This paper presents a methodology for constructing the dynamic execution graph that characterizes the execution of an ordinary program (an application program written in an imperatibve language such as C or FORTRAN) from a serial execution trace of the program. It then uses the methodology to study parallelism in the SPEC benchmarks. We see that the prallelism can be bursty in nature (periods of lots of parallelism followed by periods of little parallelism), but the average parallelism is quite high, ranging from 13 to 23,302 operations per cycle. Exposing this parallelism requires renaming of both registers and memory, though renaming registers alone exposes much of this parallelism. We also see that fairly large windows of dynamic instructions would be required to expose this parallelism from a sequential instruction stream.

Bursty bulk flows in the inner central plasma sheet

High‐speed flows in the inner central plasma sheet (first reported by Baumjohann et al. (1990)) are studied, together with the concurrent behavior of the plasma and magnetic field, by using AMPTE/IRM data from ≈ 9 to 19 RE in the Earth's magnetotail. The conclusions drawn from the detailed analysis of a representative event are reinforced by a superposed epoch analysis applied on 2 years of data. The high‐speed flows organize themselves in 10‐min time scale flow enhancements which we call bursty bulk flow (BBF) events. Both temporal and spatial effects are responsible for their bursty nature. The flow velocity exhibits peaks of very large amplitude with a characteristic time scale of the order of a minute, which are usually associated with magnetic field dipolarizations and ion temperature increases. The BBFs represent intervals of enhanced earthward convection and energy transport per unit area in the y‐z GSM direction of the order of 5×1019 ergs/RE².

Efficient communications using the meteor-burst channel

This work presents the results of a theoretical study of the meteor-burst channel which illustrates its time-varying bursty nature. In addition, the authors describe an innovative approach to data transmission over meteor-burst systems, i.e. the use of the feedback adaptive variable rate (FAVR) system which allows the maximum amount of information to be transmitted over each meteor-burst channel. For underdense meteor channels the FAVR performance is compared to an optimum system, i.e. a system capable of changing its bit rate instantaneously to channel conditions so as to maintain a constant SNR in each bit, and to a constant optimum rate/burst system. It is shown that when compared to an optimum rate per burst system, FAVR can result in a throughput increase exceeding a factor of 10. It is also shown that FAVR can approach the optimum system performance, although for practical purposes, it appears that 83-88% of optimum is attainable.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Providing Integrated Continuous Voice/Data Services to Mobile Terminals through a Power-Limited Satellite Transponder

In the very near future, Australia plans to provide integrated voice-data communication services to mobiles through its MOBILESAT system. An important component of these services would be the ability to support continuous voice and data calls between mobiles and certain fixed stations. In the context of this system, this paper describes a protocol for these services and analyzes them for the realistic situation where the satellite transponder is power-limited. Using the bursty nature of voice, an “over-assignment” strategy is proposed to efficiently utilize the satellite's resources. The problems inherent in this basic scheme are described and some simple control strategies are proposed which may be used to avoid these in an actual system.

High Data Rate Meteor-Burst Communications

The meteor burst communications channel offers a largely untapped means of communications that can alleviate congestion in many existing communications systems. It also provides some interesting advantages over other beyond-line-of-sight systems, including lower susceptibility to atmospheric perturbations, a limited footprint, and relatively low cost. Past system applications have been quite limited, however, due to the random nature of the meteor burst phenomenon which has resulted in relatively low throughput and lengthy wait-times.This paper presents the results of an experimental study of the meteor burst channel which illustrates its time-varying bursty nature. In addition, the authors describe an innovative approach to data transmission over meteor burst systems, ie, the use of the Feedback Adaptive Variable Rate (FAVR) system which allows the maximum amount of information to be transmitted over each meteor burst channel.For underdense meteor channels the FAVR performance is compared to an optimum system, ie, a system capable of changing its bit rate instantaneously to channel conditions so as to maintain a constant SNR in each bit, and to a constant optimum rate/burst system. It is shown that for such a system FAVR can result in a throughput increase exceeding a factor of 10.

The source location and beaming of broadband bursty radio emissions from Uranus

Among the radio emissions detected with Voyager 2 at Uranus was a so‐called broadband bursty or “b‐bursty” component at frequencies of 300‐700 kHz, which was first observed✓ just before closest approach and then during subsequent planetary rotations about 1‐6 hours before the more prominent smooth component. Although not obvious for individual rotations because of the bursty nature of these signals, a systematic occurrence pattern for these emissions has been detected in a new composite radio spectrogram where the bursts from different rotations were superimposed. Consisting of symmetrical emissions flanking a quiet region, with their peak frequencies occurring about an hour and a half on either side, this pattern is attributed to Voyager intercepting a hollow emission cone from the nightside of Uranus which tipped past its direction and back during successive planetary rotations. On the assumption that this cone was circular and aligned with the magnetic field at the cyclotron frequency, its source location and beam angles were determined by minimizing the apparent cone‐angle deviations at the highest frequencies. The source was thus found to occur at a southern Uranian latitude of 45°, west longitude 235°, and at a height of 1.43 RU, in excellent agreement with previous studies. The beam angle at the highest frequencies, with respect to the source magnetic field, was found to be about 85°, and that for the entire emission pattern about 80°‐87°.

Growth of electron plasma waves above and below ƒp in the electron foreshock

With increasing penetration into the electron foreshock the characteristics of the electrostatic waves driven by streaming electrons change continuously from the familiar intense waves near the electron plasma frequency ƒp to weak bursts of broadband waves initially significantly above ƒp and then well below fp. Growth well below ƒp has been demonstrated theoretically for slow, cold electron beams, and the broadband waves below ƒp in the foreshock have been interpreted in terms of the very cold or sharp “cutoff” feature of a cutoff distribution for small cutoff speeds. However, an approximate theoretical criterion indicates that the electron beams studied hitherto are unstable to reactive rather than kinetic growth, thereby favoring very narrow‐band growth contrary to the observed broadband growth. In this paper we determine conditions for kinetic growth well above and below ƒp for both cold and warm beams over a wide range of beam densities and speeds. We verify that kinetic growth below ƒp is possible for cold, slow beams and for warm, dense beams (over a wide range of beam velocities). We then argue that the observed broadband waves below fp are naturally explained in terms of slow, dilute electron beams with cold features but that an explanation involving warm, dense beams is inconsistent with the available data. Broadband growth above ƒp is explained in terms of faster, warmer beams. A unified qualitative theory for the narrow‐band and broadband waves is proposed involving (1) cutoff distributions, (2) the spatial variation in the cutoff velocity throughout the foreshock, (3) initial reactive growth with modification of the particle distribution and subsequent kinetic growth for cutoff velocities appropriate for the waves near and above ƒp, (4) initial kinetic growth and preservation of the cutoff feature for cutoff velocities appropriate to growth below ƒp, and (5) limitation of kinetic growth by inhomogeneous quasi‐linear relaxation. This theory can account qualitatively for the spatial variations in the intensity, center frequency, and bandwidth of the electron plasma waves in the foreshock. However, further work is required to understand the preservation of the cold features required for growth below ƒp and the bursty nature of the broadband waves.

Some investigations on communication switching techniques in computer networks

In realizing computer communication networks, one of the most important decisions is the proper choice of the communication scheme to be implemented at the subnet level. The selection of the best scheme depends very heavily on the nature of the traffic to be handled by the network. While the bursty nature of the computer traffic, as well as continuously decreasing cost of computer hardware, cause packet switching to be attractive; advantages of flexibility reliability and efficiency seem to favor hybrid switching. In this paper, utilizing the results of the queueing theory, we analyze three basic communication switching schemes: circuit switching; packet switching; and hybrid switching. We investigate the effects on their throughput characteristics of the parameters such as channel density, transmission efficiency, and mixture rate. Behaviour of channel density with transmission efficiency has been studied and a linear relationship is found to exist between these. The study has led to some new and interesting results which should be helpful to a designer in the choice of the proper switching scheme in various applications.

Voice Communication in Integrated Digital Voice and Data Networks

Voice communication networks have traditionally been designed to provide either analog signal paths or fixed-rate synchronous digital connections between individual subscribers. These designs were aimed at accommodating the streamlike character of speech, which has traditionally been considered to flow from source to destination at a more or less constant rate. By way of contrast, interactive and computer-to-computer data transactions tend to be bursty in nature, and this has given rise to the development of packet-switching methods for data communications. The dichotomous nature of these two major traffic classes and the apparent conflict between the types of network services they require has resulted in the deployment of separate military communications facilities for voice and data. A challenge in the design of future systems is to achieve overall economy and flexibility in the allocation of resources via the efficient integration of both traffic types in common network facilities. This paper summarizes a number of advanced concepts for switching and flow control of combined voice and data traffic in integrated environments. Performance characteristics are described based on analysis results and computer simulation studies for both multilink terrestrial and broadcast satellite network topologies.

Traffic Analysis of a Ring Switched Data Transmission System

This paper is concerned with a study of traffic and message delay in a ring switched data transmission system. The system, by asynchronous multiplexing and data storage, shares transmission facilities among many users. It is the random component of message delay due to buffering that is the focal point of our study. The basic configuration of the system is a ring connecting stations where traffic enters or leaves the system. A mathematical model of the ring is developed which accommodates an arbitrary number of stations and any given pattern of traffic between stations. Studied in detail is the uniform traffic pattern in which each user is identical and communicates equally to all others. Intrinsic to the model is a recognition of the bursty nature of data sources. Other factors that are taken into account are line and source rates as well as the blocking of data into fixed size packets. Formulas are derived from which average message delay induced by traffic in the ring can be calculated. The results of the study are presented in a set of curves where normalized delay due to traffic within specific system configurations is plotted as a function of the number of stations and source activity. The delay here is normalized to average message lengths. An important parameter of these curves is the ratio of source rate to line rate. The results show that, in certain quite reasonable circumstances, the delay is less than two average message lengths. Rings of 10, 50, and 100 users have been simulated on a digital computer. Data obtained from these investigations are presented and compared to the theoretical estimates for line busy and idle periods and message delay. The results of simulated average message delay show that, for inter-station link utilizations of about 60 percent, the difference between the theoretical estimates and experimental observations is small.

Planetary and Solar Radio Emission at 11 Meters Wavelength

Observations are described of radio emissions from the Sun, Jupiter, and Venus during 1956 and early 1957 at a wavelength of 11 meters. Records are presented of solar 11-meter radiation at the time of a large (importance 3) flare on August 31, 1956, and during other periods of solar activity. The effect of scintillation on records of radio stars also is illustrated. A number of records of impulsive radiation from Jupiter at both slow and fast recorder speeds is shown. The radiation is of a bursty or intermittent nature which can be classified into two main types: one which may persist for several seconds and produces a rumbling sound in the loudspeaker and another which is of very short duration (10 milliseconds or less) and produces a cracking or clicking sound. Many of the short pulses consist of distinct pairs or triplets which fall into two main groups, one having pulse separations of about one-quarter second and the other, pulse separations of about one tenth this value. An echo mechanism to explain the multiple pulses is postulated and observed trends in pulse separation compared to those expected with such a mechanism. The stronger Jupiter pulses indicate a peak radiated radio power at the source of the order of 10 kilowatts per cps bandwidth.