• Journal of the Korea Society of Computer and Information
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• v.13 no.6
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• pp.225-232
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• 2008

When a single source of multimedia contents is distributed to multiple reproduction devices, the audio and video contents require synchronous play for multi-channel stereo sound and lip-synchronization. The multimedia system in vehicle, especially, has researched to move to wireless environments from legacy wired environments. This paper proposes the advanced algorithm for providing synchronized services of real-time multimedia traffic in IEEE 802.11 WLANs [1]. For these, we implement the advanced IEEE 1588 Precision Time Protocol [2] and the environments for simulation. Also, we estimate and analysis performance of the algorithm, then we experiment and analysis after the porting of algorithm in wireless LAN devices (Linksys wrt-350n AP network device) to characterize timing synchronization accuracy.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.3
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• pp.575-580
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• 2017

In these days, the big-size and high resolution multimedia file is widely used through networks. To transfer and service effectively, the internet network technology is necessary to substitute broadcasting. Normally Content Delivery Network(CDN) is widely used in conventional internet for multimedia services. But it has a small bandwidth to service. So to solve this problems, many researchers have suggest the protocol for download, content distribution/saving, server synchronization, caching, pushing rate, and streaming etc. But all of these has some defects like low resolution, packets loss and delay, real application implementations etc. So, this paper suggests a new method of network protocol based on P2P collaboration and user's content using information. And it evaluated the performance of suggested method. As the results, it showed the effectiveness of 4 performances indices : download speed, decreasing rate of connected user in same time, adaptive hit ratio, traffic decreasing rate.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.8
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• pp.4025-4042
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• 2017

Session initiation protocol (SIP) is a kind of powerful and common protocols applied for the voice over internet protocol. The security and efficiency are two urgent requirements and admired properties of SIP. Recently, Hamed et al. proposed an efficient authentication and key agreement scheme for SIP. However, we demonstrate that Hamed et al.'s scheme is vulnerable to de-synchronization attack and cannot provide anonymity for users. Furthermore, we propose an improved and efficient authentication and key agreement scheme by using elliptic curve cryptosystem. Besides, we prove that the proposed scheme is provably secure by using secure formal proof based on Burrows-Abadi-Needham logic. The comparison with the relevant schemes shows that our proposed scheme has lower computation costs and can provide stronger security.

• Information Systems Review
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• v.8 no.2
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• pp.1-15
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• 2006

Schedule Management for outside duty personnels and their groups is fairly difficult since they spend most of their time on working outside individually rather than inside office. Everytime when schedule change for personnels or their groups is needed, it is necessary to call every personnel in order to notify the schedule change. It would be much easier to handle the schedule management problem if outside duty personnels are able to download schedule of their groups(and, upload their schedule) using their mobile communication devices such as PDAs. In this paper, using a data synchronization protocol in mobile communication environments, a schedule management system for outside duty personnels is designed and implemented. Data synchronization in mobile communication environments is a process of maintaining consistency between data stored in mobile devices and data stored in a (central) server at office. In other words, using SyncML data synchronization protocol proposed by OMA(Open Mobile Alliance) as an open standard for data synchronization in mobile communication environments, a schedule management system for outside duty personnels which allows them to check schedule of their groups and to notify their schedule to their groups at anytime anyplace is designed and implemented.

• IEMEK Journal of Embedded Systems and Applications
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• v.5 no.4
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• pp.217-224
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• 2010

Nowadays, people perform their tasks anywhere anytime using their mobile devices. For this reason, data synchronization (DS) between mobile devices and a central server has become one of the most essential technologies in mobile environments. Currently, several mobile DS protocols are proposed and used. However, the existing DS protocols cannot guarantee interoperability between them. To solve the problem, an embedded DS gateway has been developed in our previous study. The gateway runs on a Windows Mobile-based emulator. It converts data on a mobile device into common data specified by OMA DS standard protocol and vice versa. The embedded gateway has been built to support the OMA DS standard protocol. In order to verify that the embedded gateway conforms to the OMA DS standard protocol, two kinds of OMA conformance tests have to be conducted - interoperability test with an OMA DS-based server and conformance test with SCTS (SyncML Conformance Test Suit). In this paper, some parts of the gateway previously built are modified and the modified gateway is installed on a Windows Mobile-based smart phone. And the interoperability test and the conformance test with the SCTS are conducted. The results of the tests show that the embedded DS gateway operates properly on the Windows Mobile-based smart phone and that the gateway passes the tests, verifying its conformity to the OMA DS standard protocol. In addition, DS performance tests show that DS delay times between a real smart phone and a DS server increase gently as the number of DS data increases. In other words, the embedded DS gateway built in this paper can be used for a real smart phone at a reasonable performance cost.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.06a
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• pp.213-216
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• 2007

The paper deals with a approach to underwater acoustic based Ad-hoc communication, which allows major design strategies for Media Access Control (MAC) within a group of the autonomous underwater vehicles(AUV). The proposed MAC aims at deploying AUV-centric star topology, which minimizes overhead of sensor nodes and improves energy-efficiency. Furthermore, that is also well under long and unknown propagation delays of the underwater acoustic medium. The implemented MAC protocol makes it easier to achieve frame synchronization than TDMA due to deploying localized schedule time, in addition to saving energy consumption by letting nodes sleep. It is also superior to MACA and MACAW in terms of propagation delay. This scalable centralized protocol has the potential to serve as a primer for development of MAC protocol for future underwater acoustic based ad-hoc networks.

• Journal of IKEEE
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• v.24 no.1
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• pp.178-185
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• 2020

This paper proposes precise time synchronization-based synchronized sampling structure applied HW/SW platform for LAN-based protection of future digital substations. The integrated software of the proposed platform includes IEC 61850 protocol, IEEE 1588 precision time protocol and synchronized sampling structure. The proposed platform expected to provide a basis of an application of future distributed sensing data-based protection and control methods by providing synchronized measurement among IEDs. The implementation of the proposed HW/SW platform technique was performed using TMDXIDK572 multi-core/multi-processor evaluation module and its time synchronization performance and synchronized sampling function were confirmed through the performance tests.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.4
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• pp.684-702
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• 2011

This paper proposes a TDMA-based multichannel medium access control (MAC) protocol for QoS provisioning in mobile ad hoc networks (MANETs) that enables nodes to transmit their packets in distributed channels. The IEEE 802.11 standard supports multichannel operation at the physical (PHY) layer but its MAC protocol is designed only for a single channel. The single channel MAC protocol does not work well in multichannel environment because of the multichannel hidden terminal problem. Our proposed protocol enables nodes to utilize multiple channels by switching channels dynamically, thus increasing network throughput. Although each node of this protocol is equipped with only a single transceiver but it solves the multichannel hidden terminal problem using temporal synchronization. The proposed energy efficient multichannel MAC (EM-MAC) protocol takes the advantage of both multiple channels and TDMA, and achieves aggressive power savings by allowing nodes that are not involved in communications to go into power saving "sleep mode". We consider the problem of providing QoS guarantee to nodes as well as to maintain the most efficient use of scarce bandwidth resources. Our scheme improves network throughput and lifetime significantly, especially when the network is highly congested. The simulation results show that our proposed scheme successfully exploits multiple channels and significantly improves network performance by providing QoS guarantee in MANETs.

• 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.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.2
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• pp.165-176
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• 2015

Clock or time synchronization protocol is one of the crucial factors that could determine the quality of the communication. With the rapid development of the network technology, more robust clock synchronization algorithm is required. IEEE 1588 is one of the possible solutions for a robust clock synchronization algorithm; however, there are still some challenges that need to be concerned in IEEE 1588 in term of reducing and stabilizing the PDV value. This survey paper shows several solutions that could improve the performance of IEEE 1588, including modifying the PTP message transmission, optimizing PTP method, filtering techniques, and using the hardware timestamp instead of application layer timestamp, and so on. Despite the improvement that is created with these techniques, the clock synchronization algorithm is still an open issue in the network communication.