SUPPORTING QUALITY OF SERVICE IN HETEROGENEOUS NETWORKS: FROM ATM TO GSM

Recent years have seen significant advances in high-speed networks, highperformance end-systems and large capacity storage devices which are giving continuing impetus to the evolution of wide area distributed computing. In contrast to the ever increasing performance levels being achieved in this area, one of the most promising topics of the 1990's, mobile computing, suffers from a number of inherent constraints on the performance of the networks and end-systems it uses. Because of the widely differing technological environment of these fields, the respective research communities have tended to concentrate on separate issues and remain largely distinct. However, as we move towards global heterogeneous networks it is important that the high-speed networking and mobile computing fields converge. In this paper we argue that much state-of-the-art research in high-speed networks is of direct relevance to mobile computing. In particular, we discuss the extended use of quality-of-service (QoS) parameterisation, initially developed to support real-time processing of continuous media types, to support mobile applications; and we describe extensions to the Chorus micro-kernel to support QoS configurability over both high-speed and mobile networks. These extensions allow applications to monitor the underlying system's QoS and adapt to the type of large fluctuations in QoS which are a characteristic of mobile environments.