Support for high-performance multipoint multimedia services [chapter]

Georg Carle, Jochen Schiller, Claudia Schmidt
1994 Lecture Notes in Computer Science  
Existing and upcoming distributed multimedia applications require highly diverse services to satisfy their communication needs. Service integrated communication systems should be capable of providing high-performance real-time multipoint communication service with guaranteed quality of service (QoS). Existing communication systems and known strategies for resource reservation face increasing difficulties in fulfilling these requirements, in particular in high-speed wide area networks.
more » ... new concepts are required to support the variety of emerging applications in a heterogeneous internetworking environment. In this paper, a framework for real-time multipeer services is presented. It is based on the separation of service requirements into network bearer and transfer service requirements. The transfer service enhances the network bearer service in order to meet the service requirements of the applications. Applications and transport systems interact using an enhanced service interface, which offers several QoS parameters. The transfer service is supported by transfer components (layer 2b-4 protocol functions in end and intermediate systems), resource management functions and the integration of specialized VLSI modules for time-critical processing tasks. The hardware components can be parametrized and selected individually dependent on the required service. The transfer system guarantees specified service qualities by assigning processing resources to specific connections. Selection of the appropriate combination of components and their parametrization enhances the bearer service of the underlying network in order to provide the required multimedia service at the transport service interface. Guaranteed services are realized by the reservation of resources both in the network (for guaranteeing network bearer service) and in transfer components (for guaranteeing transfer service). The paper describes a general approach towards high performance multipeer services, and dedicated parts in more detail. Preliminary performance results of VLSI components are presented and compared with measurements of typical software implementations. Multipoint Multimedia Communication Systems Advanced multimedia applications are sensitive to the quality of service parameters throughput, delay, jitter, and reliability. Furthermore, they need to concurrently process different data streams, e.g., audio, video, and conventional data communication. Each of these streams requires a different QoS combination. As not only point-to-point but multipoint-to-multipoint communication models with several senders and receivers are needed, specific QoS parameters are associated with all members of a group or only with a subset of receivers. There is a need to accommodate traditional communication systems to these new application requirements. Therefore, several new components have to be introduced, and existing components of the communication system have to be modified. In the following, the distinct components of an enhanced communication subsystem for multimedia multipoint services are described. Enhanced Service Interface Traditionally, a limited set of QoS parameters was used to describe the requested service, and often no enforcement of these parameters was provided. Moreover, most communication protocols targeted towards pure data transfer, like TCP/IP, offer only a reliable point-to-point service (with the single QoS parameter 'reliability'). The service interface of these protocols no longer reflects the requirements of upcoming multimedia applications. These applications have strong throughput and delay requirements, while they often tolerate a reduced reliability for some communication channels. In particular, for networks under heavy load, certain data losses may be better tolerated by humans than additional delay introduced by retransmissions. Enhanced service models and interfaces are required in order to serve emerging applications. Applications and the communication system need a common language, so a source is able to specify the traffic characteristics of the flow and, in turn, the communication system guarantees a specific service. The QoS parameters throughput, delay, jitter, and reliability can be specified by a minimum, maximum, and average value. Applications prefer to specify their requirements in an application related syntax and semantics, which usually differs from the one used in the communication system. In this case, a mapping of the parameters used at the service interface valid for TSDUs (e.g., frames of a video source) to parameters inside the communication system valid for TPDUs, is necessary. Additionally, the requested service needs to be described by different service classes, which specify how the service parameters should be guaranteed. Service classes can be classified as deterministic, statistic, and best effort services. Deterministic services guarantee QoS parameters even in the worst case, statistic services guarantee QoS parameters with a given probability, and best effort services are targeted towards applications which have no specific requirements. Real time services based on statistical multiplexing achieve either statistical or best effort reliability. Fully reliable services need additional mechanisms for error correction and are therefore limited to statistical or best effort delay. The complete service is described in a service contract. In this contract, the application agrees to limit the traffic passed to the service interface, while the service provider is obliged to reserve the resources required to maintain the specified service quality. Resource Management To deliver a requested service to a particular connection, it is usually necessary to reserve certain resources in all involved communication systems for that connection [12] . Such resources are the bandwidth of a link, processing power, and buffer space.
doi:10.1007/3-540-58759-4_37 fatcat:a2yf7fub3vckpgofyesfux6wba