Real-time Quality Of Service Research Articles

Real-time quality of service with delay guarantee in sensor networks

The sensor networks raise fundamental problems for the scientific community. These problems are due to the wireless communications, the density of nodes distribution, the resources constraints (energy, processor and memory), the low nodes reliability and the strongly distributed nature of the supported application. The specific particularities of the sensor networks make it difficult the guarantee of the real-time quality of service which remains currently an important challenge. This paper presents novel protocol solutions for sensor networks in hard real-time environments. We try to get the optimisation of both constraints at the same time: real-time communication delay guarantee and the energy consumption. Our routing and medium access strategy allows the load balancing, the interferences reduction and the real-time guarantee, for being based on a dynamic generation of real-time communication trees. The simulation results show that our routing and medium access protocols help the traffic load balancing to increase the system lifetime and the guarantee of real-time traffics.

A heuristic adaptive QoS prediction scheme in single-hop passive star coupled WDM optical networks

In this paper, a novel quality of service (QoS) prediction framework is proposed to accommodate different applications with various QoS requirements. The purpose of the proposed structure is to estimate, given the QoS requirements of different applications, the number of them can be satisfied according to the predefined QoS level and the number of them have to be rejected or accepted under lower level. Moreover, this structure is able to control the network behavior when the new application with certain QoS requirements requesting for the connection. The framework consists of four modules. QoS Requirements Monitoring detects the changes in the supplied QoS. QoS Prediction performs at real-time to estimate whether the new QoS can be adapted to the current QoS. QoS Violation is dedicated to detect the violation. And a module of QoS Estimation is used to make the decision whether the hopeless new traffic is refused or accepted with acceptable QoS requirements. Therefore, this structure is able to control network behavior when the surrounding environment changes. Numerical and simulation results obtained suggest that the proposed predictive scheme is a promising approach for real time QoS prediction.

The Influence of Transport Layer to Ethernet Services Quality

Questions were analysed regarding the influence of SDH network nodes configuration specifics and TCP and UDP transport protocols on to Ethernet data transferring quality. The influence of virtual container (VC) size on ADM performance was revealed by means of mathematical model created, and it was determined, that the better choice was choosing the larger size VC, because of the smaller packets loss values obtained. The real experiments in STM-1 network helped in solving which transport protocol would be more suitable for data transferring. In case of TCP investigation, TCP windows or VC group formed in ADM size have showed the high and direct influence on to network throughput obtained, because the larger TCP windows applied assured the bigger amount of data transmitted at once. This would be meeting the requirements of Ethernet technology very effectively in high rates. The analysis of UDP showed that the most optimal UDP datagram size for Ethernet packets transferring would be of 800 – 1000 Bytes order. Investigation of UDP suitability for voice packets transferring showed that even if the smaller packet loss will have an insignificant influence on to final quality of real time services, the larger voice packets (800 – 1000 Bytes order) will assure better network throughput, smaller packets loss and Jitter values.

중복 통신 채널을 가진 CAN 시스템에서 분산 메시지 할당 방법에 관한 연구

The CAN (Controller Area Network) system is the most dominant protocol for in-vehicle networking system because it provides bounded transmission delay among ECUs (Electronic Control Units) at data rates between 125Kbps and 1Mbps. And, many automotive companies have chosen the CAN protocol for their in-vehicle networking system such as chassis network system because of its excellent communication characteristics. However, the increasing number of ECUs and the need for more intelligent functions such as ADASs (Advanced Driver Assistance Systems) or IVISs (In-Vehicle Information Systems) require a network with more network capacity and the real-time QoS (Quality-of-Service). As one approach to enhancing the network capacity of a CAN system, this paper introduces a CAN system with dual communication channel. And, this paper presents a distributed message allocation method that allocates messages to the more appropriate channel using forecast traffic of each channel. Finally, an experimental testbed using commercial off-the-shelf microcontrollers with two CAN protocol controllers was used to demonstrate the feasibility of the CAN system with dual communication channel using the distributed message allocation method.

QoS guarantee for multimedia traffic in smart homes

With the advent of home networking and widespread deployment of broadband connectivity to homes, a wealth of new services with real-time Quality of Service (QoS) requirements have emerged, e.g., Video on Demand (VoD), IP Telephony, which have to co-exist with traditional non-real-time services such as Web browsing and file downloading over the Transmission Control Protocol (TCP). The co-existence of such real-time and non-real-time services demands the residential gateway (RG) to employ bandwidth management algorithms to control the amount of non-real-time TCP traffic on the broadband access link from the Internet Service Provider (ISP) to the RG so that the bandwidth requirements of the real-time traffic are satisfied. In this paper we propose an algorithm to control the aggregate bandwidth of the incoming non-real-time TCP traffic at the RG so that QoS requirements of the real-time traffic can be guaranteed. The idea is to limit the maximum data rates of active TCP connections by dynamically manipulating their flow control window sizes based on the total available bandwidth for the non-real-time traffic. We show by simulation results that our algorithm limits the aggregate bandwidth of the non-real-time TCP traffic thus granting the real-time traffic the required bandwidth.

DLB: a novel real-time QoS control mechanism for multimedia transmission

This paper presents a new real-time Quality of Service (QoS) scheme, called Relaxed (m, k)-firm, for multimedia flow transmission which can tolerate occasional packet drops. In contrast to traditional real-time constraint, Relaxed (m, k)-firm requires the transmission delay constraint on a group of any k consecutive packets instead of imposing a transmission delay constraint per packet. Due to this relaxation, this novel scheme can achieve high resource utilisation. A new traffic control mechanism, called Double-Leaks Bucket (DLB), is also proposed to selectively drop a proportion of packets in case of network congestion while still guaranteeing the R-(m, k)-firm constraint.

Dynamic management of quality of service with priority for multimedia multicasting

We propose a receiver-oriented resource reservation mechanism, called dynamic management of QoS with priority (DMQP), for multimedia multicasting over the internet that provides quality of service (QoS) guarantees with service differentiation for heterogeneous users. In the DMQP protocol, a real-time application requests QoS by specifying a range of acceptable bandwidth values and tolerable delay durations as opposed to rigid QoS criteria. The network strives to reserve resources for the application within its bandwidth range. The service differentiation is achieved by classifying the realtime applications (or end-users) into normal and prioritised users. When the number of end-users increases, all nodes, including the receiver, sender and intermediate nodes, readjust their reserved resources dynamically to admit the new end-users, as long as their minimum bandwidth requirement is met. The DMQP provides the flexibility needed for operation in the dynamic internet environment. It has significant benefit of allowing more flexible sharing of available resources among applications.

Prediction-based real-time resource provisioning for massively multiplayer online games

Massively Multiplayer Online Games (MMOGs) are a class of computationally intensive client–server applications with severe real-time Quality of Service (QoS) requirements, such as the number of updates per second each client needs to receive from the servers for a fluent and realistic experience. To guarantee the QoS requirements, game providers currently over-provision a large amount of their resources, which makes the overall efficiency of provisioning and utilization of resources rather low and prohibits any but the largest providers from joining the market. To address this deficiency, we propose a new prediction-based method for dynamic resource provisioning and scaling of MMOGs in distributed Grid environments. Firstly, a load prediction service anticipates the future game world entity distribution from historical trace data using a fast and flexible neural network-based method. On top of it, we developed generic analytical game load models used to foresee future hot-spots that congest the game servers and make the overall environment fragmented and unplayable. Finally, a resource allocation service performs dynamic load distribution, balancing, and migration of entities that keep the game servers reasonably loaded such that the real-time QoS requirements are maintained. Experimental results based on a realistic simulation environment demonstrate the advantages of our prediction service compared to other conventional methods, especially due to its ability to adapt to different user load patterns, and a reduction of the average over-allocation from 250% (in the case of static over-provisioning) to around 25% using our dynamic provisioning method.

Real-Time Communications in Large-Scale Wireless Networks

There is an emerging need for realizing real-time quality of service (QoS) over multihop wireless communications in large-scale wireless networks. The applications can include wireless mesh infrastructure for broadband Internet access supporting multimedia services, visual sensor networks for surveillance, and disaster-relief networks. However, a number of challenges still exist as revealed by recent works, where the dataflow QoS performance such as throughput and end-to-end delay can degrade fast with the number of wireless hops. We propose to use large-scale cognitive networking methods to resolve the wireless multihop challenges. By the cognitive-networking concept, data packets travel along opportunistically available paths in the network with opportunistically available spectrum in every hop. Reliable end-to-end communications can be achieved for real-time services, where we show that (1) dataflow throughput can be independent of any number of wireless hops, (2) end-to-end delay and delay variance increase linearly with the number of wireless hops, and (3) delay variance decreases to zero with higher network density. These results are supported by analysis, simulations, and experiments.

Cross-layer modeling for quality of service guarantees over wireless links

We propose a cross-layer approach to investigate the impact of physical-layer infrastructure on data-link-layer quality-of-service (QoS) performance over wireless links in mobile networks. At the physical layer, we take multiple-input-multiple-output (MIMO) diversity schemes as well as adaptive-modulation-and-coding (AMC) techniques into account. At the data-link layer, our focus is on how this physical-layer infrastructure influences the real-time multimedia delay-bound QoS performance. To achieve this goal, we first model the physical-layer service process as a finite-state Markov chain (FSMC). Based on this FSMC model, we then characterize the QoS performance at data-link-layer using the effective capacity approach, which turns out to be critically important for the statistical QoS guarantees over wireless links in mobile networks. We also investigate the impact of physical-layer power control and channel-state information (CSI) feedback delay on the QoS performance. The numerical results obtained demonstrate that our proposed cross-layer model can efficiently characterize the interactions between the physical-layer infrastructure and data-link-layer QoS performance.

Multi-class Bandwidth Reservation Scheme Based on Mobility Prediction for Handoff in Multimedia Wireless/Mobile Cellular Networks

Next generation of wireless cellular networks aim at supporting a diverse range of multimedia services to Mobile Terminal (MT) with guaranteed Quality of Service (QoS). The challenge is to maintain the playing continuity of multimedia streams during handoff. In this paper, a bandwidth reservation scheme based on mobility prediction is proposed, to enable high accurate prediction of next crossing cell (target cell) which a MT is going to, in order to avoid too early or over reservation resulting in a waste of resources. The amount of bandwidth to be reserved is dynamically adjusted according to (a) the current position (location) and the extrapolated direction of MT and; (b) the sector and zones of the cell. A Call Admission Control scheme (CAC) is also considered to further guarantee the QoS of real time traffic. The performance of the system is evaluated through discrete event simulation of the wireless cellular environment. Simulation results show that the proposed scheme as compared to several existing schemes is able to reduce the Handoff Call Dropping Probability (HCDP) of real time traffic and the number of terminated ongoing calls of non-real time traffic. In addition, it is efficient to reduce the number of cancelled reservation and subsequently increase the system bandwidth utilization.

A QoS-Enabled Transmission Scheme for MPEG Video Streaming

While MPEG is the de facto encoding standard for video services, online video streaming service is becoming popular over the open network such as the Internet. As the performance of open network is non-predictable and uncontrollable, the tuning of the quality of service (QoS) for on-line video streaming services is difficult. In order to provide better QoS for the delivery of videos, there are proposals of new encoding formats or new transmission protocols for on-line video streaming. However, these results are not compatible with popular video players or network protocols and hence these approaches are so far not very successful. We use another approach which tries to by-pass these problems. We designed a QoS Tuning Scheme and a QoS-Enabled Transmission Scheme for transmitting MPEG videos from video servers to clients. According to the traffic characteristics between the video server and each individual client, the QoS Tuning Scheme tunes the QoS to be delivered to each individual client on the fly. Furthermore, our QoS-Enabled Transmission Scheme can be applied over any protocol, such as HTTP which is the most popular protocol over the open network. With our transmission scheme, bandwidth can be better utilized by reducing transmitted frames which would have missed their deadlines and would eventually be discarded by the clients. This is achieved by sending frames according to their impact on the QoS in the playback under the allowed throughput. With these schemes, users can enjoy video streaming through their favorite video players and with the best possible QoS. In order to facilitate the real time QoS tuning, a metric, QoS-GFS, is developed. This QoS-GFS is extended from the QoS-Index, another metric which has taken human perspective in the measurement of video quality. Hence QoS-GFS is better than the common metrics which measures QoS by means of rate of transmission of bytes or MPEG frames. We designed and implemented a middleware to perform empirical tests of the proposed transmission scheme and QoS tuning scheme. Experiment results show that our schemes can effectively enhance the QoS for online MPEG video streaming services.

A real-time loss performance monitoring scheme

Performance monitoring systems are becoming increasingly important in providing quality-of-service (QoS) based services and service guarantees. Performance monitoring can occur at different levels and different timescales. Either passive measurements or active measurements can be employed. Currently, a large amount of work has gone into developing mechanisms and protocols for performance and traffic monitoring at network level and large timescales. In comparison, little work has been done to use measurement information at small timescales for tackling network performance degradation and managing congestion in operational networks in real time. In this paper, we investigate a real-time loss performance monitoring and estimation scheme based on virtual buffer techniques. The proposed scheme is used to perform measurements at lower level, i.e. network node level, and small timescales, which can be used to provide real-time QoS information for network traffic and congestion control in ATM networks. The proposed scheme only requires modest computation resources. Virtual buffer techniques enable the scheme to obtain QoS information in a much reduced monitoring period, which is important for instantaneous network traffic and congestion control actions.

Traffic control schemes and performance analysis of multimedia service in cellular systems

This paper presents several traffic control schemes for improving the quality of service (QoS) in cellular systems. Traffic control schemes are devised for the efficient use of the limited radio resources with the increasing number of users and multimedia traffic. Both numerical analysis and computer simu- lations are carried out for the performance evaluation in terms of performance measures. Important performance measures of the suggested traffic control schemes such as the blocking probability of new traffic, the forced termination probability of handoff traffic, and the noncompletion probability for four input multimedia streams are investigated. It reveals that a finite queueing scheme for real-time handoff traffic guarantees QoS metrics, such as the blocking probability of new traffic and forced termination probability of handoff traffic, as well as efficient use of radio resources. In this paper, the priority with reserved channel and queue scheme turns out to provide significant performance improvement.

Techniques for enhancing real-time CORBA quality of service

End-to-end predictability of remote operations is essential for many fixed-priority distributed real-time and embedded (DRE) applications, such as command and control systems, manufacturing process control systems, large-scale distributed interactive simulations, and testbeam data acquisition systems. To enhance predictability, the Real-time CORBA specification defines standard middleware features that allow applications to allocate, schedule, and control key CPU, memory, and networking resources necessary to ensure end-to-end quality of service support. This paper provides two contributions to the study of Real-time CORBA middleware for DRE applications. First, we identify potential problems with ensuring predictable behavior in conventional middleware by examining the end-to-end critical code path of a remote invocation and identifying sources of unbounded priority inversions. Experimental results then illustrate how the problems we identify can yield unpredictable behavior in conventional middleware platforms. Second, we present design techniques for ensuring real-time quality of service in middleware. We show how middleware can be redesigned to use nonmultiplexed resources to eliminate sources of unbounded priority inversion. The empirical results in this paper are conducted using TAO, which is widely used and open-source DRE middleware compliant with the Real-time CORBA specification.

Multimedia synchronization based on aspect oriented programming

This paper describes an approach centered on aspect oriented programming (AOP) for controlling the synchronization of distributed multimedia systems. AOP fosters separation of concerns between application objects and synchronization aspects, which naturally arise as cross-cutting concerns. Aspect modularization and encapsulation contribute to re-usability and maintenance of both application components and control mechanisms. The paper illustrates the use of AOP technologies through the construction and evaluation of a real-time quality of service (QoS) filter regulating the QoS at the receiver-side of a multimedia system over the Internet. Aspects are programmed using AspectJ. Particular aspects are exploited for testing the temporal behavior of the synchronized system. Execution experiments make use of Java Media Framework which provides the presentation system.

Patterns and performance of distributed real-time and embedded publisher/subscriber architectures

This paper makes four contributions to the design and evaluation of publisher/subscriber architectures for distributed real-time and embedded (DRE) applications. First, it illustrates how a flexible publisher/subscriber architecture can be implemented using standard CORBA middleware. Second, it shows how to extend the standard CORBA publisher/subscriber architecture so it is suitable for DRE applications that require low latency and jitter, periodic rate-based event processing, and event filtering and correlation. Third, it explains how to address key performance-related design challenges faced when implementing a publisher/subscriber architecture suitable for DRE applications. Finally, the paper presents benchmarks that empirically demonstrate the predictability, latency, and utilization of a widely used real-time CORBA publisher/subscriber architecture. Our results demonstrate that it is possible to strike an effective balance between architectural flexibility and real-time quality of service for important classes of DRE applications.

Multiparadigm scheduling for distributed real-time embedded computing

Increasingly complex requirements, coupled with tighter economic and organizational constraints, are making it hard to build complex distributed real-time embedded (DRE) systems entirely from scratch. Therefore, the proportion of DRE systems made up of commercial-off-the-shelf (COTS) hardware and software is increasing significantly. There are relatively few systematic empirical studies, however, that illustrate how suitable COTS-based hardware and software have become for mission-critical DRE systems. This paper provides the following contributions to the study of real-time quality-of-service (QoS) assurance and performance in COTS-based DRE systems: it presents evidence that flexible configuration of COTS middleware mechanisms, and the operating system (OS) settings they use, allows DRE systems to meet critical QoS requirements over a wider range of load and jitter conditions than statically configured systems; it shows that in addition to making critical QoS assurances, noncritical QoS performance can be improved through flexible support for alternative scheduling strategies; and it presents an empirical study of three canonical scheduling strategies; specifically the conditions that predict success of a strategy for a production-quality DRE avionics mission computing system. Our results show that applying a flexible scheduling framework to COTS hardware, OSs, and middleware improves real-time QoS assurance and performance for mission-critical DRE systems.

Comparative Analysis of Scheduling Algorithms For QoS Support in Wide Area Networks

Scheduling is an important aspect of next generation wide area networks, as it plays a major role in deter mining the quality of service (QoS) a particular appli cation receives. In this paper, we discuss the main de sign issues related to scheduling and provide a frame work for the analysis of different scheduling algorithms to support the QoS requirements of multi media applications. Detailed simulation experiments, using different network parameters, including switch buffer sizes, inter-arrival rates, service rates, and net work link capacities, were conducted. Our results show that simple scheduling algorithms such as FCFS are not adequate to support real-time QoS when the network load is heavy. The results also show that more complex algorithms may be required to provide an ac ceptable level of service guarantees.

Resource Management Middleware for Dynamic, DependableReal-Time Systems

This paper presents resource management techniques that achieve the quality of service (QoS) requirements of dynamic real-time systems using open architectures and commercial off-the-shelf technologies (COTS). Dynamic real-time systems are subject to constant changes such as a varying external environment, overload of internal systems, component failure, and evolving operational requirements. Examples of such systems include the emerging generation of computer-based, command and control systems of the U.S. Navy. To enable the engineering of such systems, we present adaptive resource management middleware techniques that achieve the QoS requirements of the system. The middleware performs QoS monitoring and failure detection, QoS diagnosis, and reallocation of resources to adapt the system to achieve acceptable levels of QoS. Experimental characterizations of the middleware using a real-time benchmark illustrate its effectiveness for adapting the system for achieving the desired real-time and survivability QoS during overload situations.