K. Je#ay, D. Stone, and F. Smith. Kernel support for live digital audio and video. In Proceedings of the Second International Workshop on Network and Operating System Support for Digital Audio and Video, pages 10--21, November 1991.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....have been proposed [16, 6] to mix some form of real time support with a notion of fairness, but they do not make use of conventional real time theory. Since we are interested in systems based on a conventional RT scheduler (such as EDF or RM) we do not consider this kind of solutions. In [8], Jeffay presents a hard real time system based on EDF scheduling to be used as a test bed for video conference applications; the system can guarantee each task at its creation time based on its WCET and its minimum interarrival time. While a bound for the WCET can be found, the interarrival time ....

K. Jeffay, D. L. Stone, and F. D. Smith. Kernel support for live digital audio and video. Computer Communications, 15(6), 1992.

....Hence, it s difficult to achieve service differentiation and allocation guarantee using a best effort scheduler. In order to meet the timeliness requirements presented by multimedia applications, much work in recent years has been focusing on applying real time techniques to multimedia systems [50, 36, 70, 44, 79, 22, 10, 39, 80, 73, 72, 56]. However, most of real time schedulers require the global knowledge of the workload and the precise CPU bandwidth requirement of each application. As described in Section 1.2, such information is often hard to obtain in a dynamic environment featuring multimedia applications. Furthermore, ....

....two application threads. 1.3.3 QoS Management Level Quality of Service (QoS) represents a user s expectations for the performance of an application. It has been realized that in order to guarantee any QoS, applications must receive predictable resource allocation from the operating system [54, 10, 39, 59, 49]. Since QoS can change during the execution of the application, the resource allocation from the operating system should also provide flexibility to accommodate the dynamic QoS requirements. The effort of utilizing available resources to satisfy QoS requirements can be largely classified into two ....

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K. Jeffay, D.L. Stone, and F.D. Smith. Kernel Support for Live Digital Audio and Video. Computer Communications, 15:388--395, July/August 1992.

.... all computer systems available, as LANs, Internet and operating systems on workstations (UNIX, DOS, are asynchronous ; with real time scheduling classes appearing in UNIX systems (like in Solaris 2) it becomes possible to implement real time requirements, which was not the case before [1, 2]. Also [3] has showed that high speed wide area synchronous systems cannot be realised. Using asynchronous support to process isochronous multimedia data introduces several problems. The most important one comes from the temporal variability of computing : an operation has no upper bound. This ....

....value ; in fact, presynchronisation processes realise a temporal control of the stocker while the orchestration processes do the same on the presentation ones. Intra stream synchronisation The proposed synchronisation approach gives a solution different to the ones used in real time systems [1, 2, 10]. In an asynchronous system, upper bounds do not exist. In order to respect its maximum presentation time, the presentation process needs a real time timer with a maximal priority, thus overcoming the system asynchronism. As the orchestration process computing time and the timer expiration time ....

K. Jeffay, D.L. Stone, F.D. Smith. "Kernel support for live digital audio and video", Computer communications, Vol. 15, No. 6, July / August 1992.

.... Anderson et al. in [5] describe a multimedia operating system based on an EDF scheduler, however the quality of service (QoS) can only be guaranteed based on the WCET of each task and based on a model of the external events that can activate a task (they use a Linear Bounded Arrival Process) In [8], Je ay presents a hard real time system based on EDF scheduling to be used as a test bet for video conference applications; the system can guarantee each task at its creation time based on its WCET and its minimum inter arrival time. While a bound for the WCET can be found, the inter arrival time ....

K. Jeay, D. L. Stone, and F. D. Smith. \kernel support for live digital audio and video". Computer Communications, 15(6), 1992. 30

....environment is a particular case of the one in asynchronous environment, where asynchronism is null, and where solutions are simpler. with the real time scheduling classes in Unix (Solaris 2) it becomes possible to implement real time applications (this was not the case before) COU94] [JEF92] [JEF94b] VOG95] However, the gap between the theory of real time system and the reality of experimental realtime available systems is large [KAT94] Indeed, using real time operating systems means to solve some of the same problems as with asynchronous supports because : inputs outputs are ....

K. Jeffay, D.L. Stone, F.D. Smith, "Kernel support for live digital audio and video", Computer communications, Vol. 15, No. 6, pp 388-395, July / August 1992

....algorithm becomes straightforward: after deadline inheritance the only scheduling and preemption parameters are the deadlines. Under particular circumstances 5 EDF DCIP restricts other processes more than the original PCP. A policy similar to EDF DCIP is also used in the YARTOS kernel [4, 5]. However the task model of YARTOS is more restricted than our model. 4.2.3 Comparing BDIP and DCIP DCIP s ceilings are static and they may cause tasks that have inherited a ceiling to be non preemptable, even in case that the task for which the nonpreemptability has been organised does not show ....

K. Jeffay, D.L. Stone and F.D. Smith, "Kernel support for live digital audio and video," Computer Communications, Vol. 15, No. 6, pp. 388-395, 1992.

....system [Campbell92b] Experience with the Pandora system [Hopper90] reported in [Campbell92b] led to the observation that an audio delay greater than 10ms was noticeable without the use of echo suppression. Video can generally sustain larger values as exemplified by the 230ms estimate in [Jeffay91] but significant delay differences between streams is problematic for inter stream synchronisation. This issue is considerably less important for access to stored data, as long as the initial latency in starting a stream lies within bounds which are acceptable to a human observer. Application ....

....stream subsequently incur a delay of similar magnitude, then tolerable skew bounds could be 2 Information supplied by G. J. Stark of the University of Cambridge Computer Laboratory. 44 violated without having exceeded typical values for overall latency. A similar observation is reported in [Jeffay91] where video is delayed by up to 230ms, mainly because of the pipelined frame processing of DVI hardware. Of course, it may be possible to avoid excessive skew by arranging comprehensive QOS guarantees. This requires stream delays to be normalised and can be achieved by using additional ....

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K. Jeffay et al. Kernel Support for Live Digital Audio and Video. In Proceedings of the 2nd International Workshop on Network and Operating System Support for Digital Audio and Video, Heidelberg, Germany, November 1991. (pp 11, 45, 110)

....is a real time application. Guaranteeing the performance of real time applications requires careful construction of the system and application software using sophisticated techniques for CPU scheduling, management of data movement, synchronization, and general resource allocation and scheduling [3, 75, 57, 61, 91, 94, 103, 112]. In this dissertation, we assume the conferencing application and operating system are carefully constructed to guarantee performance of the acquisition and display pipelines, but that the network does not provide similar guarantees. 16 1.2 Network Congestion Unfortunately, even if the ....

....or type of constraint present or the network topology. 5.2.1. Video Conferencing System The video conferencing system used for the experiments in this dissertation was built at the University of North Carolina at Chapel Hill by the Distributed Real Time Systems (DiRT) research group [103] [57] [61] The hardware for this system consists of two Intel 80486 based (66 MHz) personal computers and associated video and audio hardware. The computers have 8 megabytes of RAM and use the IBM Microchannel (MCA) bus. The network adapters are IBM 16 4 MCA token ring adapters. The audio video codec ....

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Jeffay, K., Stone, D.L., and Smith, F.D., Kernel Support for Live Digital Audio and Video, Computer Communications, Vol. 16, No. 6 (July 1992), pp. 388-395.

....but the scheduler is still required to reserve the computation time. Another weakness of YARTOS is that all timing constraints must be specified as the minimum inter arrival times of task invocations. Designers using YARTOS encountered constraints which were not functions of inter arrival times [JSS92] To get around this problem, an event count was associated with each port. A kernel call was provided which returns the number of messages sent to a task. The event count can be used to implement a standard producer consumer synchronization protocol. The designer is required to know the ....

Kevin Jeffay, Donald L. Stone, and F. Donelson Smith. Kernel support for live digital audio and video. Computer Communications, 15(6):388--395, July/August 1992.

....virtual time regime so long as their combined latency does not become excessive and the data can be buffered and re timed at the edges between timing regimes. For the most part we have found that the present OS system call interface satisfies the needs of multimedia applications. Some researchers [12, 17] have advocated the use of real time schedulers to enhance multimedia performance. Others have suggested the extension of the OS interface to allow multimedia applications to specify quality of service requirements [13, 21] While these mechanisms might improve the performance of our system and ....

K. Jeffay, D. L. Stone, and F. D. Smith. Kernel Support for Live Digital Audio and Video. Computer Communications, 15(6):388--395, JulyAugust 1992.

....algorithm becomes straightforward: after deadline inheritance the only scheduling and preemption parameters are the deadlines. Under particular circumstances 6 EDF DCIP restricts other processes more than the original PCP. A policy similar to EDF DCIP is also used in the YARTOS kernel [16, 17]. However the task model of YARTOS is more restricted than our model. 4.2.3 Comparing BDIP and DCIP Both protocols maintain the mutex constraint by implication from the inheritance rule and the equality constraint. DCIP s ceilings are static and they may cause tasks that have inherited a ....

K. Jeffay, D.L. Stone and F.D. Smith, "Kernel support for live digital audio and video," Computer Communications, Vol. 15, No. 6, pp. 388-395, 1992.

....Quality To determine the region of acceptable videoconference quality, we need to define acceptable limits for videoconferences along each of the latency, jitter and data loss axes. According to Jeffay and Stone, delays of 230 milliseconds or under are acceptable for a videoconference [JSS92] For data loss, research in remote teleoperator performance has found that task performance is virtually impossible below a threshold of 3 frames per second [MS94] We use 3 frames per second as the minimum acceptable frame rate. The presence of jitter often presents an opportunity for a ....

K. Jeffay, D. Stone, and F. Smith. Kernel support for live digital audio and video. Computer Communications, 15(6), 1992.

....performance evaluation will be presented in a separate report. 8 Related Work Research on Quality of Service for multimedia applications has gained significant momentum over the last few years. Much research has been being conducted on the end system or end to end architectures for QoS support [15, 19, 8, 34, 35, 6, 32, 23, 10, 53, 43, 26, 21], and much more is on link, network and transport layer ( 55, 54, 14, 47, 50, 29, 49, 7] to name a few) Most of this research has been focused on low level system mechanisms. The authors consider and work on such parameters as period, bu#er size, jitter, bandwidth and so on. While these issues ....

K. Je#ay, D. Stone, and F. Smith. Kernel support for live digital audio and video. In Proceedings of the Second International Workshop on Network and Operating System Support for Digital Audio and Video, pages 10--21, November 1991.

....bandwidth, but the network link speed in between is limited) 1.1. Related Work Research on Quality of Service for multimedia applications has gained significant momentum over the last few years. Much research has been being conducted on the end system or end to end architectures for QoS support [11, 5, 16, 14], and much more work has been conducted on link, network and transport layer ( 28] for instance) Most of this research has been focused on low level system mechanisms. The authors consider parameters such as period, buffer size, jitter, bandwidth and so on. No doubt these are important issues ....

K. Jeffay, D. Stone, and F. Smith. Kernel support for live digital audio and video. In Proceedings of the Second International Workshop on Network and Operating System Support for Digital Audio and Video, pages 10--21, Nov. 1991.

....designed for applications with strict timing requirements, so we could use such a system for the netphone. Other researchers have demonstrated that it is possible to use real time to appear in USENIX Winter 1994 Technical Conference operating systems, for instance the YARTOS operating system [JSS92], for multimedia communication. Real time operating systems are often oriented towards command and control systems. These systems have so called hard deadlines, meaning that the cost of missing a deadline is very high. Distributed multimedia have more relaxed timing requirements. For instance, ....

....hard deadlines, meaning that the cost of missing a deadline is very high. Distributed multimedia have more relaxed timing requirements. For instance, from experiments with two way video communication, it is reported that 4 video frames out of 1000 can be lost without significant loss in of quality [JSS92]. We think that multimedia capabilities should be integrated in existing workstations, and therefore prefer to study whether current workstations can be modified to better support multimedia. In this paper, we determine how an existing operating system can be modified to allow multimedia ....

K. Jeffay, D. L. Stone, and F. Donelson Smith. Kernel support for live digital audio and video. Computer communication, 15(6):388--395, July/August 1992.

....as to the added overhead when operating systembased locking mechanisms are used. To provide a better comparison of these schemes, we provide s and r values for many common objects measured from actual object implementations. The objects were implemented under the YARTOS kernel developed at UNC [47, 77], on a 66 MHz, 80486 based IBM PC. To ensure a fair comparison, the lock and unlock calls in the YARTOS kernel were optimized as much as possible. 200 Because the 80486 does not support strong primitives other than the memory tomemory move instruction, we simulated CAS, CAS2, and MWCAS in ....

....Experiments on a Videoconferencing System In this section, we provide empirical evidence that lock free objects are superior to their lock based counterparts. This evidence comes from a set of experimental comparisons performed using a real time desktop videoconferencing system implemented at UNC [47]. We modified this system to support lock free shared objects implemented under both DM and EDF scheduling, semaphores implemented using the PCP under DM scheduling, and semaphores implemented under EDF DDM scheduling. We also considered wait free shared objects implemented under both DM and EDF ....

K. Jeffay, D. Stone, and F. D. Smith. Kernel support for live digital audio and video. Computer Communications, 15(6):388--395, July 1992.

....[43,68] In particular, supporting dynamic realtime activities with timing constraints and resource requirements that may change freely at run time stretches the traditional approach beyond its limits. Recent work in real time systems addresses some of these problems. Several systems (e.g. [3,53,113,124,125]) allow specification of timing requirements instead of forcing the programmer to determine an appropriate priority assignment. A few systems have on line admission control policies [3,78,113] but many others use off line analysis [53,124,125] Still others have no admission control at all ....

....some of these problems. Several systems (e.g. 3,53,113,124,125] allow specification of timing requirements instead of forcing the programmer to determine an appropriate priority assignment. A few systems have on line admission control policies [3,78,113] but many others use off line analysis [53,124,125]. Still others have no admission control at all [19,21,90] Some limited flexibility requirements for hard real time have been addressed recently [122] This work focuses on mode changes, which are radical but infrequent changes in the task sets of a real time system. For example, the real time ....

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K. Jeffay, D. L. Stone, and F. D. Smith. Kernel Support for Live Digital Audio and Video. Computer Communications (UK), 15(6):388--395, July-August 1992.

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Jeffay, K., Stone, D.L., Smith, F.D., 1992. Kernel Support for Live Digital Audio and Video, Computer Communications, Vol. 15, No. 6, (Jul/Aug), pp. 388-395. 206

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K. Jeffay, D. Stone, and F. D. Smith. Kernel support for live digital audio and video. Computer Communications, 15(6):388--395, 1992.

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Jeffay, K., Stone, D., and Smith, F. D. 1992. Kernel support for live digital audio and video. Computer Communications 15, 6 #July#, 388#395.

....Capture Latency (a) Case 1: 8K video frames. b) Case 2: 4K video frames. Figure 6: Capacity constraint example. and D are IBM PS 2 486 66 Mhz personal computers using IBM Intel ActionMedia I audio video adapters. The conferencing software was built at the UNC and is described elsewhere [4]. Unless otherwise stated, the conferencing system generates 60 audio frames and 30 video frames per second. Audio and video are transmitted separately as UDP messages with one frame per packet. We demonstrate a capacity constrained network by modifying the routing software in router R 1 ....

Jeffay, K., Stone, D.L., and Smith, F.D., Kernel Support for Live Digital Audio and Video, Computer Communications, Vol. 16, No. 6 (July 1992), pp. 388-395.

No context found.

K. Je#ay, D. Stone, and F. Smith. Kernel support for live digital audio and video. In Proceedings of the Second International Workshop on Network and Operating System Support for Digital Audio and Video, pages 10--21, November 1991.

No context found.

K. Jeffay, D. Stone, and F. Smith. Kernel support for live digital audio and video. In Proceedings of the Second International Workshop on Network and Operating System Support for Digital Audio and Video, pages 10--21, Nov. 1991.

No context found.

K. Jeffay, D.L. Stone, F.D. Smith, "Kernel support for live digital audio and video", Computer communications, Vol. 15, No. 6, July / August 1992

No context found.

Je#ay, K., Stone, D., Smith, F., "Kernel support for Live Digital Audio and Video", Computer Communications v15 n6, 1992.

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