Efficient Quality of Service Support in Multimedia Computer Operating Systems

This report describes our approach towards providing quality of service (QoS) guarantees for network communication within the endsystems to support multimedia applications. We first address the problem of QoS specification by identifying a set of application classes and their QoS parameters that cover the communication requirements of most applications. We then describe the QoS mapping problem, and show how requirements for resources (such as the CPU, the network interface adaptor and network connections) can be automatically derived from the application QoS parameters. We then deal with the QoS enforcement issue in which we describe techniques for scheduling protocol processing threads in order to reduce context switching overhead, as well as derive sufficiency conditions in order to provide predictable performance. We integrate all these solutions in a protocol implementation model. The key feature of the model is that protocols are part of the application process and are processed using protocol threads with individual scheduling attributes derived using our QoS mapping method. We propose several performance improvement techniques for application level protocol implementations that can reduce the high cost of data movement and context switching in these implementations. A significant component of this work will consist of implementation and experimentation which will result in significant contributions of practical utility

Distributed Data Layout, Scheduling and Playout Control in a Large Scale Multimedia Storage Server

this paper, we will consider only a retrieval environment and primarily focus on the strong interaction between the architecture, data layout, data compression, and scheduling. In particular, we will present distributed multilevel data layout, scheduling and playout control schemes developed in conjunction with our architecture. These schemes allow all clients to access the same data without data replication and support both buffered as well as bufferless clients. Also, they provide strict Large Scale Multimedia Servers 2 deterministic guarantees to each active client during normal playout as well as a full spectrum of interactive stream control operations (namely, fast forward, rewind, frame advance, slow play, slow rewind, pause, stop-and-return and stop). Our implementation of the stream control operations requires no extra bandwidth reservation and provides acceptable operation latency of a few hundread milliseconds. The rest of this paper is organized as follows: Various service models that are possible for a ondemand multimedia server are illustrated in Section 2. The basics of our prototype implementation of a large scale server are presented in Section 3. Section 4 describes the distributed and hierarchical data layout scheme. Next, our basic multilevel scheduling scheme is illustrated in Section 5. Various ways of implementing playout control operations and their implications on scheduling are described in Section 6. This section also presents modifications that must be made in the basic scheduling scheme to achieve smooth transition between normal playout and operations such as ff and rw

Catching Up With the Networks: Host I/O at Gigabit Rates

The last few years have seen network data rates skyrocket from a few Mbps to a Gbps or more. However, a lack of integration of the host-network interface, the operating system, and network protocols has resulted in end-applications seeing only a small fraction of this total bandwidth being available for data transfer. The emergence of demanding applications in the realms of multimedia and virtual reality provides further impetus in the drive to overcome this problem. In this paper, we present the design of a high performance ATM host-network interface for workstations and servers that can support a bidirectional sustained data rate in excess of a gigabit per second. A prototype of the interface is being built at Washington University as part of an ARPA-sponsored gigabit local ATM testbed. Our interface design, which emphasizes seamless integration with the OS and network protocols, features: support for streaming data from I/O devices (e.g., cameras, disk arrays, etc.) to the network or vice-versa, as well as from device-to-device, while bypassing the main system bus; an ATM interconnect that extends to the desk-area; a zero-copy interface to system memory that is achieved through the use of page remapping techniques; full AAL-5 segmentation and reas-sembly; pacing control that provides for single-parameter bandwidth reservation; a high degree of scalabil-ity in terms of the number of I/O devices that can be simultaneously supported; low-cost (one ASIC); and multiprocessor support

Real-time Upcalls: A Mechanism to Provide Real-time Processing Guarantees

Real-time upcalls (RTUs) are an operating systems mechanism that can be used by applications to efficiently schedule code segments (or handlers) that must execute periodically. While the mechanism was conceived to support protocol processing with quality-of-service guarantees for networked multimedia applications it is general enough to be applicable in other domains like real-time image processing. Until now real-time threads have been the only mechanism for implementing protocols in user space with QoS guarantees. The RTU mechanism avoids the implementation complexity of the thread based approach while retaining its ability to ensure real-time behavior. In addition, our design simplifies protocol code, improves performance, and can be ported to most systems. A key feature of RTU scheduling is the pre-emption scheme that exploits the iterative nature of protocol processing by allowing an RTU to yield the CPU by returning from the invocation. This obviates the need for RTU handlers to..

Design and Implementation of a Versatile Multimedia Network Interface and I/O Chip

We present an I/O architecture that is particularly well suited to the transport and delivery of continuous media data to devices distributed in the desk or home area. Our design makes use of the APIC chip, which is a high performance (1.2 Gb/s) research prototype of an ATM network interface that we have developed at Washington University. Both hardware and software issues are considered. Due to space constraints, this extended abstract will only touch on aspects of our architecture that we consider important. More details will be presented in the full-length version of the paper. + This work was supported in part by the Advanced Research Projects Agency (ARPA), the National Science Foundation (NSF), and an industrial consortium of Ascom Nexion, Bay Networks, Bell Northern Research, NEC America, NIH, NTT, Samsung, Southwestern Bell, and Tektronix. Page 1 Extended Abstract Introduction Although gigabit network design has seen major advances in the last decade, it is a well known f..

Load Balance Properties of Distributed Data Layouts for Clustered MOD Servers

Large scale storage servers that provide location transparent, interactive access to hundreds or thousands of concurrent, independent clients will be important components of the future information super-highway infrastructure. Two key requirements of such servers are as follows: support high parallelism and concurrency in data access to allow large number of access to the same or different data. Second, support independent interactive playout control operations such as fast-forward, rewind, slow-play, pause, resume, random access etc. with minimal latency. This paper assumes a distributed storage server architecture consisting of several high performance storage nodes interconnected by a high speed desk area network into a cluster as a candidate architecture that can meet these two requirements. For such an architecture, we explore generalized distributed data layouts to satisfy the requirement of large number of scalable concurrent data accesses. We also quantify certain interesting p..