On the Implementation of a Quality of Service Controlled ATM Based Communications System in Chorus

In this paper we describe the design of a QoS driven communications stack in a microkernel operating system environment. The paper focuses on resource management aspects of the design and in particular we deal with CPU scheduling, network resource management and memory management issues. We describe an API at which QoS parameters are supplied by users and present an architecture able to guarantee these QoS requirements with varying degrees of commitment. The architecture includes modules to translate user level QoS parameters into representations usable by the scheduling, network and memory management subsystem. It also incorporates admission tests which determine whether or not a new connection can be accepted given a particular QoS requirement and resource availability. In addition to predictable resource allocation the architecture also incorporates dynamic QoS management which ensures that ongoing commitments continue to be met in the face of variable loading.