• The KIPS Transactions:PartD
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• v.12D no.6 s.102
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• pp.915-920
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• 2005

In this paper we expanded a existing web based B2B system to support users in low speed network. To guarantee shared dat a consistency between clients and a server, we proposed a method of data change detection by using a time stamp tree and the performance analysis of the proposed method was proved by a simulation. Under the worst condition that leaf nodes of a times tamp tree were changed uniform distribution, the simulation result showed that the proposed method was more efficient than a sequential detection until the percentage of changed nodes were below $15\%$. According to our observation, the monthly average of data change was below $7\%$ on a web-based construction MRO B2B system or a company A from April 2004 to August 2004. Therefore the Proposed method improved performance of data change detection in practice. The proposed method also reduced storage consumption in a server because it didn't require a server to store replicated data for every client.

• Journal of Korea Multimedia Society
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• v.9 no.8
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• pp.1020-1029
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• 2006

Realization of high-capacity quality-of-service router needs fair packet schedulers with a lower complexity. Timestamp based fair packet schedulers have the ideal complexity of O(log V), where V is the maximum number of admitted flows, but it has been recently reduced to O(1) using bin concept. However, the latency property was deteriorated and the bandwidth utilization was also declined. In addition, traffic flows requiring strong delay bound may not be admitted. To overcome these problems, this paper proposes a Mini-Bin based Start-Time (MBST) scheduler with variable complexity and evaluates its performance. The MBST scheduler uses the timestamp calculation scheme of start-time based schedulers to enhance the bandwidth utilization and also introduces mini-bin concept to improve the latency, The performance evaluation shows that the proposed scheduler can reduce the complexity of the legacy start-tine based schedulers by $1.8{\sim}5$ times without deteriorating the bandwidth utilization property.

• Journal of KIISE:Information Networking
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• v.35 no.6
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• pp.529-537
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• 2008

AODV routing protocol is intended for use by mobile' nodes in an ad-hoc network. In AODV nodes create routes on an on-demand basis. As the degree of node mobility becomes high, however, the number of the control packets, RREQ and RREP messages, have increased so rapidly. The unexpected increases in the number of the control packets cause the destination node to decrease the packet receiving rate and also to increase the overall energy consumption of such a network. In this paper, we propose a novel method of adaptively controlling the occurrences of such RREQ messages based on AIAD (additive increase additive decrease) under a consideration of the current network status. We have tested our proposed method with the conventional AODV and the method using timestamp based on the three performance metrics, i.e.. how long does node moves, node velocity, and node density, to compare their performance.

• The KIPS Transactions:PartD
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• v.10D no.4
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• pp.647-654
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• 2003

The replication of data is used to increase its availability and to improve the performance of a system. The distributed database system has to maintain both the database consistency and the replica consistency. This paper proposes an algorithm which resolves the conflict of the operations by using the mechanism based on the structure that the replicas of each data item are hierarchically organized. Each update is propagated along the tree based on the fact that the root of each data item is the primary replica in partially replicated databases. The use of a hierarchy of data may eliminate useless propagation since the propagation can be done only to sites having the replicas. In consequence, the propagation delay of updates may be reduced. By using the timestamp and a compensating transaction, our algorithm resolves the non-serializability problem caused by the conflict of operations that can happen on the way of the update propagation due to the lazy propagation. This resolution also guarantees the data consistency.

• The KIPS Transactions:PartC
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• v.13C no.2 s.105
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• pp.203-210
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• 2006

Fair packet scheduling algorithms supporting quality-of-services of real-time multimedia applications can be classified into the following two design schemes in terms of the reference time used in calculating the timestamp of arriving packet: Finish-time Design (FD) and Start-time Design (SD) schemes. Since the former can adjust the latency of a flow with raising the flow's reserved rate, it has been applied to a router for the guaranteed service of the IETF (Internet Engineering Task Force) IntServ model. However, the FD scheme may incur severe bandwidth loss for traffic flows requiring low-rate but strong delay bound such as internet phone. In order to verify the usefulness of the SD scheme based router for the IETF guaranteed service, this paper analyzes and compares two design schemes in terms of bandwidth and payload utilizations. It is analytically proved that the SD scheme is better bandwidth utilization than the FD one, and the simulation result shows that the SD scheme gives better payload utilization by up to 20%.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.1
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• pp.177-182
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• 2016

Geofence is a generic concept for describing geographic aspects of PoI(Point of Interest) enabling users to proactively induce context-based actions. However there is no need to maintain continuity when you reflect geofence in case of temporary events, accidents and isolation. Therefore we propose a geofence platform so-called TemG by adding time-limited information to support PoI. The proposed geofence platform TemG ensures the persistency and continuity of geofence. Furthermore, the proposed TemG can not only provide to automatically activate or deactivate the specified geofence during a period of timestamp but also support to the basic context-aware service knowing in/out in the zone. In the near future, the proposed TemG will be need to extend HPS(Hybrid Positioning System) for IoT(Internet of Things).

• Journal of Internet Computing and Services
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• v.10 no.4
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• pp.223-230
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• 2009

Among the remote user authentication schemes, password-based authentication methods are the most widely used. In 2004, Das et al. proposed a "Dynamic ID Based Remote User Authentication Scheme" that is the password based scheme with smart-cards, and is the light-weight technique using only one-way hash algorithm and XOR calculation. This scheme adopts a dynamic ID that protects against ID-theft attack, and can resist replay attack with timestamp features. Later, many flaws of this scheme were founded that it allows any passwords to be authenticated, and can be vulnerable to impersonation attack, and guessing attack. By this reason many modifications were announced. These scheme including all modifications are similarly maintained security against replay the authentication message attack by the timestamp. But, if advisory can replay the login immediately, this attempt can be succeeded. In this paper, we analyze the security vulnerabilities of Das scheme, and propose improved scheme which can resist on real-time replay attack using the counter of authentication. Besides our scheme still secure against impersonation attack, guessing attack, and also provides mutual authentication feature.

• The KIPS Transactions:PartC
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• v.10C no.7
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• pp.923-928
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• 2003

This paper proposes a bottleneck link bandwidth measurement algorithm for reducing packet transmission delay within the grid network. There are two methods for measuring bottleneck link bandwidth：Packet Pair algorithm and Paced Probes algorithm. They measure bottleneck link bandwidth using the difference in arrival times of two paced probe packets of the same size traveling from the same source to destination. In addition, they reduce the influences of cross traffic by pacer packet. But there are some problems on these algorithms：it's not possible to know where bottleneck link occurred because they only focus on measuring the smallest link bandwidth along the path without considering bandwidth of every link on the path. So hop-by-hop based bottleneck link bandwidth measurement algorithm can be used for reducing packet transmission delay on grid network. Timestamp option was used on the paced probe packet for the link level measurement of bottleneck bandwidth. And the reducing of packet transmission delay was simulated by the solving a bottleneck link. The algorithm suggested in this paper can contribute to data transmission ensuring FTP and realtime QoS by detecting bandwidth and the location where bottleneck link occurred.

• The KIPS Transactions:PartA
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• v.15A no.2
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• pp.87-94
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• 2008

Message races should be detected for debugging effectively message-passing programs because they can cause non-deterministic executions of a program. Previous tools for detecting message races report that message races occur in every receive operation which is expected to receive any messages. However message races might not occur in the receive operation if each of messages is transmitted through a different logical communication channel so that their incorrect detection makes it a difficult task for programmers to debug programs. In this paper we suggest a tool, MPIRace-Check, which can exactly detect message races by checking the concurrency between send/receive operations, and by inspecting the logical communication channels of the messages. To detect message races, this tool uses the vector timestamp to check if send and receive operations are concurrent during an execution of a program and it also uses the message envelop to inspect if the logical communication channels of transmitted messages are the same. In our experiment, we show that our tool can exactly detect message races with efficiency using MPI_RTED and a benchmark program. By detecting message races exactly, therefore, our tool enables programmers to develop reliable parallel programs reducing the burden of debugging.

• Journal of the Korea Society of Computer and Information
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• v.18 no.10
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• pp.71-80
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• 2013

In this paper, we analyze the security vulnerability through the several attack scenarios for the MCR-MAP(Multi-Context RFID Mutual Authentication Protocol) proposed by Ahn et al. And we propose the secure mutual authentication protocol that improved a prior MCR-MAP. The suggested protocol uses the ID of the legal tag and the timestamp generated by the server, when the tag tries to authenticate. And when the tag creates the credential, we create the new secret key computing the XOR operation between the secret key shared with the server and the tag timestamp generated by the server. As a result, the proposed protocol provides the secure mutual authentication and then is safe to spoofing attack. Also it provides forward-secrecy and then is safe to offline brute-burst attack. In this paper, we compare and verify the security vulnerability of the prior and the proposed protocol through the security analysis.