Quality of Service Support for Protocol Processing within Endsystems

Abstract

We describe a framework for providing quality-of-service (QoS) guarantees within the endsystem for networked multimedia applications. There are four components in this framework namely—QoS specification, QoS mapping, QoS enforcement, and protocol implementation. QoS specifications are at a high level, and use a small number of parameters to allow applications greater ease in specifying their requirements. Based on the QoS specifications, QoS mapping operations derive resource requirements for each end-to-end session of the application. Important resources considered are the cpu and the network connection. The third component of the framework is QoS enforcement. Enforcement is mainly concerned with providing real-time processing guarantees for protocol code during data transfer. We have implemented a real-time upcall (rtu) facility which is an enhancement to the well known upcall mechanism for structuring protocols, rtus are scheduled using a policy called rate monotonie with delayed pre-emption (rmdp) that takes advantage of the iterative nature of protocol processing to reduce context switching overhead and increase scheduling efficiency. The last component of our framework is an application level protocol implementation model. Protocol code is structured as rtus with attributes that are derived from high level specifications by the QoS mapping operations. We describe techniques to reduce the cost of data movement and context switching in such implementations. The rtu mechanism currently runs in the Netbsd os on Sparc and Pentium based platforms. Initial measurements show that it is an effective means to implement protocols with QoS support.