Acceptable Quality Of Service Research Articles

Analysis of bandwidth allocation schemes for transmission of VBR video traffic on a FODA satellite network

FODA, an access protocol for satellite networks based on a TDMA technology, is designed to support integrated services. To this end, FODA provides two types of service: synchronous and asynchronous; only the users of the synchronous service have guaranteed bandwidth. In the paper the authors focus on the synchronous service alone and investigate static bandwidth allocation strategies which satisfy the quality of service (QoS) requirements (i.e. a limited transfer delay and a packet loss rate < 10-6) for the transmission of the data generated by a variable bit rate (VBR) video codec. By solving an analytical model it is shown that, due to the stringent QoS constraints, the amount of reserved bandwidth for VBR video applications must be much higher than their throughput. Hence a portion of low-priority traffic (e.g. EDP data) can be transmitted on the FODA synchronous services to utilise the satellite link to the maximum extent. Via simulation, the authors analyse, for the bandwidth allocation schemes which provide an acceptable QoS for high-priority traffic, the QoS available to low-priority users.

Real-time applications in a CRMA network: a performance analysis

This paper analyses bandwidth allocation schemes for managing real-time applications (Variable Bit Rate video and voice) in a CRMA network. A methodology to compute the Quality of Service (QoS) experienced by variable bit rate (VBR) video and voice sources is proposed. As VBR video applications only tolerate extremely low packet loss rates (< 10 −8), we need a computational approach to estimate very low tail probabilities. Studying the QoS with a simulation technique is not feasible, because computational costs make it almost impossible to estimate tail distribution probabilities lower than 10 −2−10 −3. Therefore, to achieve this target, we propose a model which represents a CRMA network's worst case behaviour (i.e. a scenario with maximum network congestion), and which can be solved analytically. By solving this model for different bandwidth allocation schemes, we can obtain the corresponding bounds on the QoS experienced by VBR video users. Finally, for those bandwidth allocation schemes which provide an acceptable QoS for VBR video traffic, we also estimate (via a trace-driven simulation) the QoS achieved by voice users.

Finite-Horizon Statistical Quality-of-Service Measures for High-Speed Networks

Future high-speed networks (HSNs) are expected to support a wide variety of services such as voice and video and provide a guaranteed quality-of-service (QOS). Traditionally, the computation of user-oriented performance criteria such as the average delay has been carried out via steady state analysis of queueing theoretic models of communication networks. In this paper, we show that the steady state analysis is not entirely sufficient for QOS purposes in future high-speed networks as it yields long-run performance measures that are not appropriate for envisaged applications in HSNs. New QOS criteria for such applications are proposed and their computation detailed for some simple queueing models. These new QOS criteria essentially capture the network performance over the short-run and are more accurate indicators of the actual user-perceived quality of, for example, audio or video. For the numerical examples presented in this paper, our focus will be primarily on the fractional packet loss and we will be interested in the probability (frequency) of occurence of high or low loss “periods.” When our interest is in maximizing the occurence of no loss periods, we show for the M/M/1/K queue that reasonably high values of traffic load may be supported and fairly good QOS (as defined in this paper) provided to applications. In this context, steady state analysis is found to be woefully inadequate. On the other hand, when we are interested in minimizing the occurence of high loss periods, we find for a packet voice multiplexer that large values of the carried load may not be supportable while providing an acceptable QOS.

Policing of realistic VBR video traffic in an ATM network

AbstractATM has been accepted by CCITT as the transport mechanism for the future BISDN and will also be widely used in future customer premises networks. Networks based on the ATM principle are expected to provide a very flexible communications infrastructure allowing customers to make effective use of a wide variety of offered services. To provide this flexibility with an acceptable quality of service while operating the network in an economic way, elaborate traffic management functions will be necessary to control the traffic flows within the network. This paper will study one of these functions—the so‐called ‘usage parameter control’ or ‘policing’ function—in some detail to illustrate some of the problems that arise and point out possible solutions. The mechanisms chosen to implement the policing function will be the ‘leaky bucket’ mechanism, the ‘jumping window’ mechanism and the ‘moving window’ mechanism. The input streams used to assess the mechanisms represent different types of video communication—videophone, video conference and entertainment video—coded according to different variable bit‐rate (VBR) algorithms. In contrast to most of the previous studies, where artificial, statistical traffic sources have been used, the sources used in this paper are directly based on measured ‘real‐life’ video data. This ensures that all the statistical properties of the actual traffic stream are preserved and allows identification of the different factors that influence the dimensioning and the performance of the policing mechanism. The results of this study show that the uncertainty about the key parameters at call set‐up and the considerable impact of single scenes make the proper dimensioning of policing mechanisms difficult. Furthermore, it seems not to be practical to use the long term mean bit‐rate as the key traffic control parameter for these sources. Results indicating that the long‐term cell loss ratio is not a sufficient measure for the quality of service are also presented. A comparison of the mechanisms shows that from a performance perspective, the ‘leaky bucket’ mechanism is superior to the two window mechanisms. This work is relevant to evolving standards for both BISDN traffic management and variable bit‐rate video coding.

Modeling and performance comparison of policing mechanisms for ATM networks

Asynchronous transfer mode (ATM) networks, as proposed by CCITT as the solution for the future broadband ISDN, will provide high flexibility with respect to the varying bandwidth requirements of the different services. They will also support variable bit rates within a connection. The packetized information transfer, without flow control between the user and the network, in combination with the asynchronous multiplexing principle, results in a need to control the individual cell stream during the entire duration of the calls to ensure an acceptable quality of service for all coexisting calls sharing the same network resources. This kind of control will be provided by introducing a policing or usage parameter control function. Basic design objectives and requirements for such a function are described. These requirements serve as a basis for the comparison of some of the mechanisms proposed so far, namely the leaky bucket, the jumping window, the triggered jumping window, the moving window, and the exponentially weighted moving average mechanisms. >

Implementation of conservation voltage reduction at Commonwealth Edison

The implementation of a conservation voltage reduction program is described. Such a program involves the calibration of substation voltage-regulating equipment so that distribution system voltages are maintained at as low a level as possible within the standard acceptable range. Initial distribution system voltmeter data were used to estimate potential voltage reductions. Program results show that an average reduction of 1.6 V was achieved. Comparison of this result with the initial estimate indicates that the feasibility of additional voltage reductions depends on the definition of acceptable service quality.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Citizens-band radio

In recent years the requirement for the introduction of a two-way speech facility for the public at large has gradually increased. This facility has become well known as citizens-band radio (CB), and is used extensively in the USA and most Western European countries. Equipments operate using frequency modulation, amplitude modulation, single sideband and generally utilise the frequency band 26.960 MHz to 27.4 MHz. Until now it has been the policy of the UK Home Office Radio Regulatory Department to assign frequencies essentially for business or commercial use. However, the provision of a CB service has been reviewed by the Home Office, taking into account the political, economic, social and technical factors, and on balance it was considered that the introduction of a CB service would be of some benefit to the public as a whole. The Radio Regulatory Department conducted detailed technical studies to identify frequency bands and other parameters which would minimise the interference experienced by existing radiocommunication services; and at the same time provide the user with an acceptable quality of service. After extensive public consultation and careful consideration the Home Office introduced a legal CB service, employing frequency modulation only, for operation in two different frequency bands at 27 and 900 MHz, respectively.