The peer-to-peer (P2P) architecture provides support for the next generation of information sharing applications. A difficult challenge faced by these systems in the presence of non-uniform data distribution and dynamic network conditions is load sharing. This paper addresses the problem of load sharing in P2P networks across heterogeneous super-peers. We propose two load sharing techniques that use data replication to improve access performance. In the first technique, called periodic push-based replication (PPR), super-peers periodically send replicas of the most frequently accessed files to remote super-peers. This effectively reduces the hop count to fetch these files. The second technique, called on-demand replication (ODR), performs replication based on access frequency. By performing replication on-demand, ODR provides adaptability to changes in access behavior. Extensive testing have been conducted to study the performance of the proposed techniques. The results obtained demonstrate significant performance improvements through replication

Mobile clients often need to operate while disconnected from the network due to limited battery life and network coverage. Hoarding supports this by fetching frequently accessed data into clients' local caches prior to disconnection. Existing work on hoarding have focused on improving data accessibility for individual mobile clients. However, due to storage limitations, mobile clients may not be able to hoard every data object they need. This leads to cache misses and disruption to clients' operations. In this paper, a new concept called cooperative hoarding is introduced to reduce the risks of cache misses for mobile clients. Cooperative hoarding takes advantage of group mobility behaviour, combined with peer cooperation in ad-hoc mode, to improve hoard performance. Two cooperative hoarding approaches are proposed that take into account access frequency, connection probability, and cache size of mobile clients so that hoarding can be performed cooperatively. Simulation results show that the proposed methods significantly improve cache hit ratio and provides better support for disconnected operations compared to existing schemes.

In this paper, we introduce the concept of cooperative hoarding to reduce the risks of cache misses for mobile clients. Cooperative hoarding takes advantage of group mobility behaviour, combined with peer cooperation in ad-hoc mode, to improve hoard performance. Two cooperative hoarding approaches that take into account clients' access frequencies, connection probabilities and cache size when performing hoarding are proposed. Test results show that the proposed methods significantly improve cache hit ratio and reduce query costs compared to existing approaches.

Existing Web services rely on HTTP and TCP as the underlying transport protocols for SOAP messaging. While these protocols provide a number of benefits, including being able to pass through firewalls and are universally supported across different platforms, they were designed for wired networks with high bandwidth, low latency and low error rate transmissions. Due to the variability of wireless channels however, these assumptions do not hold in wireless environments. In this paper, we investigate the performance of HTTP and TCP as transport protocols for SOAP in wireless environments. Through extensive testing, we show that SOAP-over-HTTP and SOAP-over-TCP are inefficient and lead to high latency and transmission overhead for wireless applications. To overcome these limitations, we study the use of UDP as a binding protocol for SOAP. The results obtained are promising and show that SOAP-over-UDP provides throughput that is ten times higher compared to SOAP-over-HTTP in a wireless setting. Furthermore, using UDP to transport SOAP messages reduces transmission overhead by more than 50% compared to SOAP-over-HTTP. Finally, to illustrate where UDP binding can be useful, example applications are also described in this paper

Traditional cache replacement policies rely on the temporal locality of users' access pattern to improve cache performance. These policies, however, are not ideal in supporting mobile clients. As mobile clients can move freely from one location to another, their access pattern not only exhibits temporal locality, but also exhibits spatial locality. In order to ensure efficient cache utilisation, it is important to take into consideration the location and movement direction of mobile clients when performing cache replacement. In this paper. we propose a mobility-aware cache replacement policy, called MARS, suitable for wireless environments. MARS takes into account important factors (e.g. client access rate, access probability, update probability and client location) in order to improve the effectiveness of onboard caching for mobile clients. Test results show that MARS consistently outperforms existing cache replacement policies and significantly improves mobile clients' cache hit ratio.

Recent advances in wireless communication and global positioning technologies have led to increasing interest in location dependent information services. As mobile users move between locations utilising such services, their access patterns not only exhibit temporal locality, but also spatial locality. Traditional cache replacement policies were designed to deal with temporal locality, as a result, they are inefficient location dependent services. In this paper a mobility-aware algorithm called MARS+ is proposed to detect regular client movement patterns and provides information to improve cache performance. Test results show that MARS+ improves clients' cache hit ratio by more than 16% compared to existing policies.

Object caching is often used to improve the performance of mobile applications, but the gain is often lessened by the additional load of maintaining consistency between an original object and its cached copy. This paper aims at reducing the consistency maintenance work and proposes a protocol that distinguishes between two classes of consistency (i.e. weak and strong) and treats them differently. Strong consistency is used for data that needs to be consistent all the time, whereas weak consistency is for cases when stale data can be tolerated or only specific updates are relevant to the application. Consistency is maintained by using strict and permissive read/write time locks that enable data sharing for a fixed time period and support concurrency control. A notification protocol for propagating updates to clients is also proposed. Performance tests have shown that switching from strong to weak consistency reduces the number of aborts due to conflicting operations by almost half even with high read/write sharing.