• The Journal of Korean Institute of Next Generation Computing
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• v.13 no.6
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• pp.7-20
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• 2017

The advancement of cloud and big data and the considerable growth of traffic have increased the complexity and problems in the management inefficiency of existing networks. The software-defined networking (SDN) environment has been developed to solve this problem. SDN enables us to control network equipment through programming by separating the transmission and control functions of the equipment. Accordingly, several studies have been conducted to improve the performance of SDN controllers, such as the method of connecting existing legacy equipment with SDN, the packet management method for efficient data communication, and the method of distributing controller load in a centralized architecture. However, there is insufficient research on the control of SDN in terms of the quality of network-using applications. To support the establishment and change of the routing paths that meet the required network service quality, we require a mechanism to identify network requirements based on a contract for application network service quality and to collect information about the current network status and identify the violations of network service quality. This study proposes a method of identifying the quality violations of network paths through ontology to ensure the network service quality of applications and provide efficient services in an SDN environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8A
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• pp.1134-1143
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• 2000

We propose a scheduling algorithm, Bandwidth Allocation Scheme (BAS), that guarantees bounded delay in a switching node. It is based on the notion of the GPS (Generalized Processor Sharing) mechanism, which has clarified the concept of fair queueing with a fluid-flow hypothesis of traffic modeling. The main objective of this paper is to determine the session-level weights that define the GPS sewer. The way of introducing and derivation of the so-called system equation' implies the approach we take. With multiple classes of traffic, we define a set of service curves:one for each class. Constrained to the required profiles of individual service curves for delay satisfaction, the sets of weights are determined as a function of both the delay requirements and the traffic parameters. The schedulability test conditions, which are necessary to implement the call admission control, are also derived to ensure the proposed bandwidth allocation scheme' be able to support delay guarantees for all accepted classes of traffic. It is noticeable that the values of weights are tunable rather than fixed in accordance with the varying system status. This feature of adaptability is beneficial towards the enhanced efficiency of bandwidth sharing.

• Journal of the Institute of Convergence Signal Processing
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• v.6 no.2
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• pp.95-99
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• 2005

This paper presents an accurate recovery method of the reference clock which is needed for network synchronization in two-way satellite multimedia systems compliant with DVB-RCS specification and which use closed loop method for burst synchronization. In these systems, the remote station transmits TDMA burst via return link. For burst synchronization, it obtains reference clock from program clock reference (PCR) defined by MPEG-2 system specification. The PCR is generated periodically at the hub system by sampling system clock which runs at 27MHz $\pm$ 30ppm. Since the reference clock is recovered by means of digital PLL(DPLL) using imprecise PCR values due to variable random jitter, the recovered clock frequency of remote station doesn't exactly match reference clock of hub station. We propose a robust recovery method of reference clock against random delay jitter The simulation results show that the recovery error is remarkably decreased from 5 clocks to 1 clock of 27MHz relative to the general DPLL recovery method.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.05a
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• pp.241-244
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• 2012

In mobile ad-hoc networks, it should be the most important issue to reduce the power consumption of communications, because the resource of a node is limited in these networks. In existing cluster-based routing protocols, cluster headers participate in almost all communication processes. Therefore the lifetime of the cluster header is shortened and it does not have the effective route. In the proposed cluster-based routing protocol, the cluster header transmits a control packet which gives the route information to member nodes. This makes that the cluster header decreases the number of participating in communications, and that node members do not have to communicate trough the cluster header. This results in extending the lifetime of the cluster header, and having the effective route, data transmission rate and improved stability of routes.

• The Journal of the Korea Contents Association
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• v.6 no.7
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• pp.58-68
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• 2006

There are two traditional scheduling methods known as PQ and WRR in the DiffServ network, however, these two scheduling methods have some drawbacks. In this paper, we propose an algorithm that can be adopted in WRR scheduler with making up for weak points of PQ and WRR. The proposed algorithm produces the control discipline by the fuzzy theory to dynamically assign the weight of WRR scheduler with checking the Queue status of each class. To evaluate the performance of the proposed algorithm, We accomplished a computer simulation using NS-2. From simulation results, the proposed algorithm improves the packet loss rate of the EF class traffic to 6.5% by comparison with WRR scheduling method and that of the AF4 class traffic to 45% by comparison with PQ scheduling method.

• Journal of Internet Computing and Services
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• v.6 no.3
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• pp.71-84
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• 2005

Recently, the expert call center solution has become the center of interest, since finance and tele-marketing system, which is focused on a communication industry, have been increasing, Specially, the call center market is growing up with a supporting Caller-ID for a cellular phone in Korea, In the present, although large size companies are developing expensive solutions and instruments to service only for the big companies, there little solutions for SOHO markets, Therefore, in this paper we have shown a design and an implementation of a CTI system which is capable of in/outbound call processing by using CTI, and providing stable services by linking the customer's DB. And these functionalities have become possible by integrating functions of PBX and the computer control of the PBX. First, we have constructed call flows and analyzed packets for the standard communication through the PBX in call. Then, we have designed and implemented a middleware which linked a call between a client and a customer. Finally, we have constructed a database module for applying the CRM technology to the management of customer's contents.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.5
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• pp.772-778
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• 2018

Due to the recent advances in computing, communication and micro-electromechanical technology, Wireless Sensor Networks (WSNs) applications have been extended from military to many commercial areas such as object tracking, wire detection, and vehicular sensor networks. In some applications bursty data from many sensor nodes may be generated and the generated data from the monitoring area may be sent in a limited time to the final destination, sink node. In this paper, we present a BTF-MAC protocol adequate for WSNs applications in which bursty data packets are required to be transmitted in a limited time. The BTF-MAC is a synchronous duty-cycle MAC protocol and uses a slot-reserved and operational period extension mechanism adapted to the traffics. Our numerical analysis and simulation results show that BTF-MAC outperforms other related protocols such as DW-MAC and SR-MAC in terms of energy consumption and transmission delay.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.4
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• pp.800-806
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• 2015

WAVE(Wireless Access in Vehicular Environments) system is wireless communication technology that vehicle sends and receives packets between vehicles or between vehicles and infrastructure in a high-speed mobile environment. In this study, we have designed and implemented a CRL(Certificate Revocation List) download protocol that is used to verify certificate revocation status of the other party when the vehicles communicate with WAVE system. This protocol operates over UDP. And to support security features, also, ECDSA(Elliptic Curve Digital Signature Algorithm) is used for mutual authentication and ECIES(Elliptic Curve Integrated Encryption Scheme) is used to ensure the confidentiality. Moreover, this protocol ensures the integrity of data by adding MAC(Message Authentication Code) to the end of packet and support the error and flow control mechanisms.

• The Journal of the Korea Contents Association
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• v.10 no.9
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• pp.79-87
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• 2010

This paper proposes a L3 handover method to minimize packet loss for supporting service continuity to IMS Terminal which has a single WLAN interface. The existing IMS based handover solution is able to support handover between different access networks in case that a terminal has multiple interfaces. That is, WLAN terminals need multiple interfaces to connect with one or more access networks. This proposed method configures IP address for the terminal in target WLAN previously by using Candidate Access Router Discovery(CARD) mechanism. Also, in the proposed method, service continuity server performs L3 connection establishment in target WLAN and registration to IMS server instead of the terminal. And then session control mechanism based on SIP is performed to support service continuity. We analyzed handover latency and signaling cost in the proposed method and existing method to show the improved performance by the proposed method.

• Journal of KIISE:Computer Systems and Theory
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• v.35 no.4
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• pp.150-157
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• 2008

This paper presents a design and implementation of realtime video player that operates on a tiled-display system consisting of multiple PCs to provide a very large and high resolution display. In the proposed system, the master process transmits a compressed video stream to multiple PCs using UDP multicast. All slaves(PC) receive the same video stream, decompress, clip their designated areas from the decompressed video frame, and display it to their displays while being synchronized with each other. A simple synchronization mechanism based on the H/W clock of each slave is proposed to avoid the skew between the tiles of the display, and a flow-control mechanism based on the bit-rate of the video stream and a pre-buffering scheme are proposed to prevent the jitter The proposed system is implemented with Microsoft DirectX filter technology in order to decouple the video/audio codec from the player.