• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.6
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• pp.1689-1706
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• 2012

The preservation of temporal dependencies among a group of processes that exchange continuous media at runtime is a key issue for emerging mobile distributed systems (MDS), such as monitoring of biosignals and interactive multiuser games. Although several works are oriented to satisfy temporal dependencies, most of them are not suitable for MDSs. In general, an MDS is characterized by the absence of global references (e.g. shared memory and wall clock), host mobility, limited processing and storage capabilities in mobile hosts, and limited bandwidth on wireless communication channels. This paper proposes an asymmetric synchronization protocol to be used at runtime in an MDS without using a common reference. One main aspect of our synchronization protocol is that it translates temporal constraints to causal dependencies of the continuous media data as seen by the mobile hosts. We simulate the protocol by considering a cellular network environment and by using MPEG-4 encoders. The simulation results show that our protocol is effective in reducing the synchronization error. In addition, the protocol is efficient in terms of processing and storage costs at the mobile devices, as well as in the overhead attached per message across the wired and wireless channels.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.253-256
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• 2009

Synchronization system which applies to two-way synchronization of spatio-temporal in the mobile environment maintains a consistence of DB from some defect during synchronization. This study analyzes defects that are generated at the mobile client-server environment and proposes recovery protocol which can rerun consistence of DB and synchronization.

• The KIPS Transactions:PartD
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• v.11D no.4
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• pp.783-798
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• 2004

An e-business client application in ubiquitous mobile computing environment may become disconnected from the enterprise server due to broken communication connections caused by the limitation of mobile computing environments(limited battery life of the mobile device, low bandwidth communication, incomplete wireless communication infrastructure, etc). It Is even Possible that mobile client application Intentionally operates in disconnected mode to reduce communication cost and the power consumption of the mobile device. We use “data hoarding” as a means of providing local autonomy to allow transactions to be processed and committed on the mobile host despite of disconnection. The key problem to this approach is the synchronization problem that serialize potentially conflicting updates from disconnected clients on master objects of the server database. In this paper, we present a new transaction synchronizing method that splits a transaction into a set of independent component transactions and give the synchronization priority on each component taking the possibility of use and conflicts in the server into consideration. Synchronization is performed component by component based un synchronization priority. After the Preferred component of a no bile transaction succeeds in synchronization with the server, the mobile transaction can pre-commit at server. A pre-committed transaction's updated value is made visible at server before the final commit of the transaction. The synchronization of the component with low synchronization priority can be delayed in adaption to wireless bandwidth and computing resources. As a result, the availability of important data updated by mobile client is increased and it can maximize the utilization of the limited wireless bandwidth and computing resources.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.4
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• pp.909-916
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• 2010

In ubiquitous GIS services is possible to use the spatio-temporal data using a mobile device at anytime. Also, client is transmitted latest spatio-temporal data from server. But traditional systems have a problem that the time of transmitting latest information from server to client takes long time because of collecting data periodically. In this paper, we proposed Two-way Synchronization system supporting field update to solve the existing problem. This system uses mobile device for collecting changed data in the real world and sending collected data to server.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.12
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• pp.2226-2231
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• 2008

As the mobile devices and the wireless networks have high-performance capabilities, it is possible to synchronize the spatio-temporal data of a server with the spatio-temporal data of a mobile device which are collected at a field. However, since the server process the synchronization which the model device requests, the whole synchronizations of mass mobile devices take long time. In this paper, we propose the scheme to process concurrently the synchronizations of mobile devices to use multi-queue which does not conflict.

• Journal of KIISE:Databases
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• v.34 no.4
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• pp.357-368
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• 2007

This paper proposes the SAMD(Synchronization Algorithms based on Message Digest) algorithm based on message digest in order to data synchronization between a database server and a mobile database. The SAMD algorithm makes the images at the database server and the mobile database using message digest tables and compares two images in order to select the rows needed to synchronization. If two images are different, the synchronization is progressed according to synchronization policy. The SAMD algorithm does not use techniques which are dependent the some database vendor and also triggers, stored procedures and timestamps. The SAMD only uses the standard SQL functions for the synchronization. Therefore the SAMD algorithm is used in any combinations of the database server and the mobile database because the SAMD algorithm is not depended on some database venders. Also the SAMD algorithm shows better performance compared with existing synchronization products.

• The KIPS Transactions:PartC
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• v.12C no.5 s.101
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• pp.741-748
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• 2005

SyncML is an open standard data synchronization protocol proposed by OMA(Open Mobile Alliance). In this paper, a Session Handler module, one of major modules for developing SyncML data synchronization clients, and a client User Setup program are designed and implemented. The Session Handier Module controls communication sessions, generates header parts of messages exchanged, and determines the legitimacy of incoming messages. In order to justify normal operations of the Session Handler module and the client User Setup program implemented In this paper, they are ported to a Zaurus PDA, which runs on LINUX operating system. In addition, data synchronization operations are performed between the PDA and a Synthesis sever, whose SyncML data synchronization operation is certificated by OMA, Wireless Internet International Standard Forum.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.927-928
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• 2016

In the past, the way of sharing data in various devices was to use a physical method such as USBs. The radical development of communications technology and the users, who possess various multimedia devices, caused the need for the new way that people could share their data in various devices, and providing various digital resources by using the cloud computing service helps people solve the limit to sharing the resources in their PC. Therefore, this paper is to suggest the technology for synchronization of mobile devices, and the user-centered cloud service is applied to the technology. Having conducted the experiment, it has been discovered that applying the synchronization of mobile devices using the cloud service enabled to conduct the auto file synchronization and to minimize the bandwidth consumed during the synchronization process between two devices.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.3 no.4
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• pp.344-365
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• 2009

The performance of a tracking system is greatly increased if multiple types of sensors are combined to achieve the objective of the tracking instead of relying on single type of sensor. To conduct the multi-modal tracking, we have previously developed a multi-modal sensor-based tracking model where acoustic sensors mainly track the objects and visual sensors compensate the tracking errors [1]. In this paper, we find a network synchronization problem appearing in the developed tracking system. The problem is caused by the different location and traffic characteristics of multi-modal sensors and non-synchronized arrival of the captured sensor data at a processing server. To effectively deliver the sensor data, we propose a time-based packet aggregation algorithm where the acoustic sensor data are aggregated based on the sampling time and sent to the server. The delivered acoustic sensor data is then compensated by visual images to correct the tracking errors and such a compensation process improves the tracking accuracy in ideal case. However, in real situations, the tracking improvement from visual compensation can be severely degraded due to the aforementioned network synchronization problem, the impact of which is analyzed by simulations in this paper. To resolve the network synchronization problem, we differentiate the service level of sensor traffic based on Weight Round Robin (WRR) scheduling at the routers. The weighting factor allocated to each queue is calculated by a proposed Delay-based Weight Allocation (DWA) algorithm. From the simulations, we show the traffic differentiation model can mitigate the non-synchronization of sensor data. Finally, we analyze expected traffic behaviors of the tracking system in terms of acoustic sampling interval and visual image size.

• Journal of the Korea Society of Computer and Information
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• v.17 no.2
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• pp.13-21
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• 2012

Mobile data caching is usually used as an effective way to improve the speed of local transaction processing and reduce server load. In mobile database environment, due to its characters - low bandwidth, excessive latency and intermittent network, caching is especially crucial. A lot of mobile data caching strategies have been proposed to handle these problems over the last few years. However, with smart phone widely application these approaches cannot support vast data requirements efficiently. In this paper, to make full use of cache data, lower wireless transmission quantity and raise transaction success rate, we design a new mobile data caching synchronization strategy based on in-demand and replacement priority. We experimentally verify that our techniques significantly reduce quantity of wireless transmission and improve transaction success rate, especially when mobile client request a large amount of data.