QoS Support for Mobile Computing

Abstract

In recent y ears small, completely portable computers have become available on the marketplace. There is demand for such computers, termed walkstations, to access network services while retaining their mobility, a n d t o operate e ectively in a wide range of conditions. Future o ce environments are expected to support wireless networks with bandwidths which are several orders of magnitude greater than are available outdoors. In such e n vironments, there will be powerful compute servers available for a walkstation's use.This dissertation describes a novel architecture called Notus and its supportfor applications operating in a mobile environment. The concept of the traded hando is introduced, where applications are able to participate in the hando process, rebuilding connections to the most appropriate service. This is expected to bene t walkstations which roam over large distances, where connections to servers would otherwise be strained, and also between heterogeneous networks where cooperation between the networks in performing a hando might be problematic. It is also proposed in this dissertation that applications could bene t from the ability to migrate onto compute servers as a walkstation moves into the o ce environment. This enables both the walkstation to conserve its own resources, and applications to improve the service provided to the end user. Finally, b y i n terleaving a traded hando with the migration process, it is possible for a migrating application to easily rebuild its connections as it moves to a new host.The Notus architecture has beenimplemented, including a traded hando service, and a new application migration service. The new application migration service was designed since existing application migration services are unsuited to mobile environments and it enables applications to migrate between heterogeneous hosts with little disruption. Applications which use the service are written in a standard, compiled language, and normal running applications suffer little overhead. A n umber of existing applications which a r e representative of a walkstation's interactive desk-top environment have beenadapted to use the Notus architecture, and are evaluated.In summary, this work describes how mobility awareness and the support from appropriate tools, can enable walkstation applications to better adapt to a changing mobile environment, particularly when the walkstation is carried between di erent n e t work types or over great distances. To Catherina PrefaceExcept where otherwise stated in the text, this dissertation is the result of my o wn work and is not the outcome of work done in collaboration.This dissertation is not substantially the same as any I h a ve submitted for a degree or diploma or any other quali cation at any other university.No part of my dissertation has already been, or is being currently submitted for any such degree, diploma or other quali cation.This dissertation does not exceed sixty thousand words, including tables, footnotes, and bibliography.Publications Some ...

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