Chong Sun Hwang

Efficient, Energy Conserving Transaction Processing in Wireless Data Broadcast

Broadcasting in wireless mobile computing environments is an effective technique to disseminate information to a massive number of clients equipped with powerful, battery operated devices. To conserve the usage of energy, which is a scarce resource, the information to be broadcast must be organized so that the client can selectively tune in at the desired portion of the broadcast. In this paper, the efficient, energy conserving transaction processing in mobile broadcast environments is examined with widely accepted approaches to indexed data organizations suited for a single item retrieval. The basic idea is to share the index information on multiple data items based on the predeclaration technique. The analytical and simulation studies have been performed to evaluate the effectiveness of our methodology, showing that predeclaration-based transaction processing with selective tuning ability can provide a significant performance improvement of battery life, while retaining a low access time. Tolerance to access failures during transaction processing is also described

Using predeclaration for efficient read-only transaction processing in wireless data broadcast

Wireless data broadcast allows a large number of users to retrieve data simultaneously in mobile databases, resulting in an efficient way of using the scarce wireless bandwidth. However, the efficiency of data access methods is limited by an inherent property that data can only be accessed strictly sequentially by users. To properly cope with the inherent property, this paper presents three predeclaration-based transaction processing methods that yield a significant performance improvement in wireless data broadcast.

A causal message logging protocol for mobile nodes in mobile computing systems

This paper presents a causal message logging protocol with independent checkpointing for mobile nodes with the aim of efficiently handling several constraints of the mobile nodes such as mobility and disconnection, limited life of battery power, small amount of storage and low bandwidth on wireless link. For this purpose, the protocol includes a low-cost failure-free mechanism requiring only locating the mobility agent maintaining the latest checkpoint of each process on an mobile node during its handoff process. This mechanism forces only the latest checkpoint to be maintained on the stable storage while incurring low failure-free overhead. Also, the protocol uses two garbage collection schemes to remove log information of mobile nodes. The first scheme enables each mobile node to autonomously remove useless log information in its storage by piggybacking only some additional information without requiring any extra message and forced checkpoint. The second scheme allows the mobile node to remove a part of log information in its storage if more empty storage space is required after executing the first scheme. It reduces the number of processes to participate in the garbage collection by using the size of the log information of each process. Simulation results show that the two proposed schemes significantly reduce the garbage collection overhead compared with traditional schemes. Additionally, we present an efficient recovery algorithm to avoid frequent stable storage accesses, impose no restriction on the execution of live processes during recovery and ensure consistent recovery in case of being integrated with independent checkpointing.

History-Based Auxiliary Mobility Management Strategy for Hierarchical Mobile IPv6 Networks

The reduction of the signaling load associated with IP mobility management is one of the significant challenges to IP mobility support protocols. Hierarchical Mobile IPv6 (HMIPv6) aims to reduce the number of the signaling messages in the backbone networks, and improve handoff performance by reducing handoff latency. However, this does not imply any change to the periodic binding update (BU) to the home agent (HA) and the correspondent node (CN), and now a mobile node (MN) additionally should send it to the mobility anchor point (MAP). Moreover, the MAP should tunnel the received packets to be routed to the MN. These facts mean that the reduction of the BU messages in the backbone networks can be achieved at the expense of the increase in the signaling bandwidth consumption within a MAP domain. On the other hand, it is observed that an MN may habitually stay for a relatively long time or spend on using much Internet in a specific cell (hereafter, home cell) covering its home, office or laboratory, etc. Thus, considering the preceding facts and observation, HMIPv6 may not be favorable especially during a home cell residence time in terms of signaling bandwidth consumption. To overcome these drawbacks of HMIPv6, we propose a history-based auxiliary mobility management strategy (H-HMIPv6) to enable an MN to selectively switch its mobility management protocols according to whether it is currently in its home cell or not in HMIPv6 networks. The operation of H-HMIPv6 is almost the same as that of HMIPv6 except either when an MN enters/leaves its home cell or while it stays in its home cell. Once an MN knows using its history that it enters its home cell, it behaves as if it operates in Mobile IPv6 (MIPv6), not in HMIPv6, until it leaves its home cell; No periodic BU messages to the MAP and no packet tunneling occur during the MNs home cell residence time. The numerical results indicate that compared with HMIPv6, H-HMIPv6 has apparent potential to reduce the signaling bandwidth consumption and the MAP blocking probability.

Region-based stage construction protocol for fault tolerant execution of mobile agent

Fault tolerance is essential to the development of reliable mobile agent systems in order to guarantee continuous execution of mobile agents. For this purpose, previous work has proposed fault tolerant protocols for mobile agent execution based on stage construction. However, when previous protocols are applied to a multiregion mobile agent computing environment, the overhead of work such as monitoring, election, voting and agreement is increased. We propose a region-based stage construction (RBSC) protocol for fault tolerant execution of mobile agents in a multiregion mobile agent computing environment. The RBSC protocol uses new concepts of quasiparticipant and substage in order to put together some places located in different regions within a stage in the same region. Therefore, the RBSC protocol decreases the overhead of stage works. Consequently, the RBSC protocol decreases the total execution time of mobile agents.

Considering mobility patterns in moving objects database

What is important in location-aware services is how to track moving objects efficiently. To this end, an efficient protocol which updates location information in a location server is highly needed. In fact, the performance of a location update strategy highly depends on the assumed mobility pattern. In most existing works, however, the mobility issue has been disregarded and too simplified as linear function of time. We propose a new mobility model, namely state-based mobility model (SMM) to provide more generalized framework for both describing the mobility and updating location information of moving objects. We also introduce the state-based location update protocol (SLUP) based on this mobility model

Efficient Cache Management Protocol Based on Data Locality in Mobile DBMSs

In mobile client-server database systems, caching of frequently accessed data is an important technique that will reduce the contention on the narrow bandwidth wireless channel. As the server in mobile environments may not have any information about the state of its clients cache(stateless server), using broadcasting approach to transmit the list of updated data to numerous concurrent mobile clients is an attractive approach. In this paper, a new caching method is proposed to support transaction semantics at mobile clients. The proposed protocol adopts adaptive broadcasting as the way of sending invalidation reports, in order to dynamically adapt to system workload (update pattern, data locality). We study the performance of the proposed protocol by means of simulation experiments.

Hybrid checkpointing protocol based on selective-sender-based message logging

This paper presents a hybrid checkpointing protocol-an asynchronous checkpointing protocol using a message sending/receiving state change for reducing the overhead of failure-free operation combined with a selective sender-based message logging protocol for reducing the cascade rollback of asynchronous checkpointing protocol. The selective sender-based message logging protocol records only potential orphan messages when taking a checkpoint. And this paper presents a message dependency tree recording the inter-process message sending/receiving information on a volatile storage for reducing the search time of inter-process information during the failure recovery.

An authentication protocol based on CBRP in ad hoc network

Mobile and wireless network technology is growing at a rapidly changing in nowadays. Ad hoc networks are a new wireless networking paradigm for mobile host. Ad hoc networks do not rely on any fixed infrastructure such as base stations as mobile switching. Mobile hosts rely on each other to keep the network connected. Ad hoc networks are often designed for specific environments and may have to operate with full availability even in difficult conditions. In this paper, we detail security threat against ad hoc routing protocols, specifically examining CBRP. Our authentication protocol based on CBRP(APBC) design an end-to-end message authentication scheme that relies on mutual trust between nodes in other clusters. The strategy of APBC is to take advantage of the multi-layer architecture that is designed for authentication protocol in CHs(Ciuster Head) using MCH(Main CH). We have proposed an authentication protocol that uses certificates contain Diffie-Hellman key agreement and a multi-layer architecture at the physical layer so that the number of encryption needed, thereby reducing the computational overheads and successfully defeated all identified attacks. We also use new authentication protocol schemes, such as MCH using Challenge-Response identification protocol to build a highly secure and highly available authentication protocol service, which forms the core of our security framework.

Authentication based on multilayer clustering in ad hoc networks

In this paper, we describe a secure cluster-routing protocol based on a multilayer scheme in ad hoc networks. This work provides scalable, threshold authentication scheme in ad hoc networks. We present detailed security threats against ad hoc routing protocols, specifically examining cluster-based routing. Our proposed protocol, called authentication based on multilayer clustering for ad hoc networks (AMCAN), designs an end-to-end authentication protocol that relies on mutual trust between nodes in other clusters. The AMCAN strategy takes advantage of a multilayer architecture that is designed for an authentication protocol in a cluster head (CH) using a new concept of control cluster head (CCH) scheme. We propose an authentication protocol that uses certificates containing an asymmetric key and a multilayer architecture so that the CCH is achieved using the threshold scheme, thereby reducing the computational overhead and successfully defeating all identified attacks. We also use a more extensive area, such as a CCH, using an identification protocol to build a highly secure, highly available authentication service, which forms the core of our security framework.