Location and routing optimization protocols supporting internet host mobility

PhD ThesisWith the popularity of portable computers and the proliferation of wireless networking interfaces, there is currently a great deal of interest in providing IP networking support for host mobility using the Internet as a foundation for wireless networking. Most proposed solutions depend on a default route through the mobile host's horne address, which makes for unnecessarily long routes. The major problem that this gives rise to is that of finding an efficient way of locating and routing that allows datagrams to be delivered efficiently to moving destinations whilst limiting costly Internet-wide location updates as much as possible. Two concepts - "local region" and "patron service" - are introduced based on the locality features of the host movement and packet traffic patterns. For each mobile host, the local region is a set of designated subnetworks within which a mobile host often moves, and the patrons are the hosts from which the majority of traffic for the mobile host originated. By making use of the hierarchical addressing and routing structure of Internet, the two concepts are used to confine the effects of a host moving, so location updates are sent only to a designated host moving area and to those hosts which are most likely to call again, thus providing nearly optimal routing for most communication. The proposed scheme was implemented as an IP extension using a network simulator and evaluated from a system performance point of view. The results show a significant reduction in the accumulated communication time along with improved datagram tunneling, as compared with its extra location overhead. In addition, a comparison with another scheme shows that our functionality is more effective both for location update and routing efficiency. The scheme offers improved network and host scalability by isolating local movement from the rest of the world, and provides a convenient point at which to perform administration functions

Coordinated adaptation for adaptive context-aware applications

The ability to adapt to change is critical to both mobile and context-aware applications. This thesis argues that providing sufficient support for adaptive context-aware applications requires support for coordinated adaptation. Specifically, the main argument of this thesis is that coordinated adaptation requires applications to delegate adaptation control to an entity that can receive state information from multiple applications and trigger adaptation in multiple applications. Furthermore, coordination requires support for reconfiguration of the adaptive behaviour and user involvement. Failure to support coordinated adaptation is shown to lead to poor system and application performance and insufficient support for user requirements. An investigation of the existing state-of-the-art in the areas of adaptive and context- aware systems and an analysis of the limitations of existing systems leads to the establishment of a set of design requirements for the support of coordinated adaptation. Specifically, adaptation control should be decoupled from the mechanisms implementing the adaptive behaviour of the applications, applications should externalise both state information and the adaptive mechanisms they support and the adaptation control mechanism should allow modifications without the need for re-implementation of either the application or the support platform. This thesis presents the design of a platform derived from the aforementioned re- quirements. This platform utilises a policy based mechanism for controlling adaptation. Based on the particular requirements of adaptive context-aware applications a new pol- icy language is defined derived from Kowalsky’s Event Calculus logic programming formalism. This policy language allows the specification of policy rules where condi- tions are defined through the expression of temporal relationships between events and entities that represent duration (i.e. fluents). A prototype implementation of this design allowed the evaluation of the features offered by this platform. This evaluation reveals that the platform can support coordinated adaptation with acceptable performance cost.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Proceedings of the Fifth International Mobile Satellite Conference 1997

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments

The Effects of Mobility on Reliable Transport Protocols

We explore the effects of host motion on the performance of active transport-level connections. Motion causes increased delays and packet losses while the network learns how to deliver data to a host's new location. Transport protocols incorrectly interpret these delays and losses as signs of network congestion. They consequently throttle their transmissions, further degrading performance. We quantify this degradation through measurements of protocol behavior in a wireless networking testbed. We show how retransmission backoffs introduce unacceptably long pauses in transport-level communication (0.9 seconds and longer), and how the slow growth of transmission windows prevents connections from again reaching maximum throughput for significant periods of time (1 second and longer). Our results demonstrate that transport protocols must be made aware of host motion, and identify which aspects of these protocols must be adapted to mobile computing environments. 1 Introduction Reliable tran..