A system of distributing video and/or audio information employs digital signal processing to achieve high rates of data compression. The compressed and encoded audio and/or video information is sent over standard telephone, cable or satellite broadcast channels to a receiver specified by a subscriber of the service, preferably in less than real time, for later playback and optional recording on standard audio and/or video tape.

Audio and video transmission and receiving system

For applications relying on the transfer of multimedia, and in particular continuous media, it is essential that quality of service (QoS) is guaranteed system-wide, including end-systems, communications systems and networks. Although researchers have addressed many isolated areas of QoS provision, little attention has so far been paid to the definition of an integrated and coherent framework that incorporates QoS interfaces, management and mechanisms across all architectural layers. To address this deficiency, we are developing a Quality of Service Architecture (QoS-A) which offers a framework to specify and implement the required performance properties of multimedia applications over high-performance ATM-based networks. The QoS-A incorporates the notions of flow, service contract and flow management. Flows characterise the production, transmission and eventual consumption of single media streams, service contracts are binding agreements between users and providers and flow management provides for the monitoring and maintenance of the contracted QoS levels. This paper provides an overview of the QoS-A and focuses particularly on the role of the transport service and protocol in the architecture. We describe a multimedia enhanced transport service (METS), flow management and transport layer service contract. We show how QoS levels contracted at the transport service interface can be assured in the context of our local ATM environment.

https://cs.dartmouth.edu/~campbell/papers/thesis.pdf

A quality of service architecture

Multimedia applications have timing requirements that cannot generally be satisfied using the time-sharing scheduling algorithms of general purpose operating systems. The authors provide the predictability of real-time systems while retaining the flexibility of a time-sharing system. They designed a processor capacity reservation mechanism that isolates programs from the timing and execution characteristics of other programs in the same way that a memory protection system isolates them from outside memory accesses. In the paper, they describe a scheduling framework that supports reservation and admission control, and introduce a novel reserve abstraction, specifically designed for the microkernel architecture, for measuring and controlling processor usage. The authors have implemented processor capacity reserves in Real-Time Mach, and they describe the performance of their system on several types of applications. >

/pdf/processor-capacity-reserves-operating-system-support-for-40oa161yh8.pdf

Processor capacity reserves: operating system support for multimedia applications

A video teleconferencing method and apparatus for computer workstations connected by a digital data network includes a transmission source portion for a local workstation to send audio and video teleconference data across the network to one or more remote workstations, and, a receiver for the local workstation to receive audio and video teleconference data back from the remote workstations. The local workstation sends teleconference data to each of the remote workstations over a variable bandwidth digital data connection, and each of the remote workstations returns teleconference data back to the local workstation over another variable bandwidth digital data connection. The transmission source portion includes a master software process executing on the local workstation, and the receiver includes a slave software process executing the remote workstation. The master process of a local workstation causes execution of a slave process on a remote workstation for receiving video teleconference data from the local workstation. An audio data transmitter for sends an audio data stream to the remote workstation such that the audio data can be reconstructed into a continuous audio signal. A video transmitter sends video data so that each frame of video data to be sent is inserted into the audio data stream without affecting the continuity of the reconstructed audio signal at the remote workstation.

Video teleconferencing for networked workstations

Workstations and personal computers are increasingly being used for applications with real-time characteristics such as speech understanding and synthesis, media computations and I/O, and animation, often concurrently executed with traditional non-real-time workloads. This paper presents a system that can schedule multiple independent activities so that: . activities can obtain minimum guaranteed execution rates with application-specified reservation granularities via CPU Reservations, CPU Reservations, which are of the form reserve X units of time out of every Y units, provide not just an average case execution rate of X/Y over long periods of time, but the stronger guarantee that from any instant of time, by Y time units later, the activity will have executed for at least X time units, . applications can use Time Constraints to schedule tasks by deadlines, with on-time completion guaranteed for tasks with accepted constraints, and . both CPU Reservations and Time Constraints are implemented very efficiently. In particular, . CPU scheduling overhead is bounded by a constant and is not a function of the number of schedulable tasks. Other key scheduler properties are: . activities cannot violate other activities' guarantees, . time constraints and CPU reservations may be used together, separately, or not at all (which gives a round-robin schedule), with well-defined interactions between all combinations, and . spare CPU time is fairly shared among all activities. The Rialto operating system, developed at Microsoft Research, achieves these goals by using a precomputed schedule, which is the fundamental basis of this work.

CPU reservations and time constraints: efficient, predictable scheduling of independent activities

The DASH resource model is defined as a basis for reserving and scheduling resources (disk, CPU, network, etc.) involved in end-to-end handling of continuous-media (information flowing continuously over real time i.e. digital audio or digital video) data. The model uses primitives that express work-load characteristics and performance requirements, and defines an algorithm for negotiated reservation of distributed resources. This algorithm is embodied in the session reservation protocol, a backward-compatible extension of the Internet Protocol. Hardware trends and future applications that motivate the DASH resource model are described. The performance requirements for using continuous media and the limitations of existing systems are discussed. The DASH resource model for reserving and scheduling resources is presented. The DASH kernel is briefly described. >

S.-Y. Tzou

Papers

Support for continuous media in the DASH system