• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.1
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• pp.323-342
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• 2021

Personal health records (PHRs) is an electronic medical system that enables patients to acquire, manage and share their health data. Nevertheless, data confidentiality and user privacy in PHRs have not been handled completely. As a fine-grained access control over health data, ciphertext-policy attribute-based encryption (CP-ABE) has an ability to guarantee data confidentiality. However, existing CP-ABE solutions for PHRs are facing some new challenges in access control, such as policy privacy disclosure and dynamic policy update. In terms of addressing these problems, we propose a privacy protection and dynamic share system (PPADS) based on CP-ABE for PHRs, which supports full policy hiding and flexible access control. In the system, attribute information of access policy is fully hidden by attribute bloom filter. Moreover, data user produces a transforming key for the PHRs Cloud to change access policy dynamically. Furthermore, relied on security analysis, PPADS is selectively secure under standard model. Finally, the performance comparisons and simulation results demonstrate that PPADS is suitable for PHRs.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.1
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• pp.344-357
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• 2015

With the increase in a number of access technologies and data rates, a continuous connection among different networks is demand of the future wireless networks. In the last decade, user connectivity among different access networks remained a challenging job. Therefore, in this article, we proposed a user-centric and user-perspective based network selection mechanism for fast handover management in heterogeneous wireless networks. The proposed scheme selects the most appropriate network among available networks on the basis of resources i.e. cost, data rate, and link quality. Initially, we load the Media Independent Information Service (MIIS) with the information of cost and data rate provided by different network operators. Similarly, Mobile Node (MN) is also loaded with the user preferred cost and data rate for different applications. The MN obtains the information of cost and data rate from MIIS server upon a predefined threshold, and make a decision for handover according to its current cost and data rate. Furthermore, we employ an optimal threshold mechanism for initiation of the handover execution phase to minimize false handover indications. The proposed scheme is based on a survey for network selection and its implementation in C programming language to validate its performance and accuracy. The simulation result shows that the proposed scheme performs superior then the schemes present in the current literature.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.2
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• pp.683-701
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• 2012

IEEE 802.11 standard has achieved huge success in the past decade and is still under development to provide higher physical data rate and better quality of service (QoS). An important problem for the development and optimization of IEEE 802.11 networks is the modeling of the MAC layer channel access protocol. Although there are already many theoretic analysis for the 802.11 MAC protocol in the literature, most of the models focus on the saturated traffic and assume infinite buffer at the MAC layer. In this paper we develop a unified analytical model for IEEE 802.11 MAC protocol in ad hoc networks. The impacts of channel access parameters, traffic rate and buffer size at the MAC layer are modeled with the assistance of a generalized Markov chain and an M/G/1/K queue model. The performance of throughput, packet delivery delay and dropping probability can be achieved. Extensive simulations show the analytical model is highly accurate. From the analytical model it is shown that for practical buffer configuration (e.g. buffer size larger than one), we can maximize the total throughput and reduce the packet blocking probability (due to limited buffer size) and the average queuing delay to zero by effectively controlling the offered load. The average MAC layer service delay as well as its standard deviation, is also much lower than that in saturated conditions and has an upper bound. It is also observed that the optimal load is very close to the maximum achievable throughput regardless of the number of stations or buffer size. Moreover, the model is scalable for performance analysis of 802.11e in unsaturated conditions and 802.11 ad hoc networks with heterogenous traffic flows.

• Proceedings of the KIEE Conference
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• 2005.10b
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• pp.397-399
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• 2005

Handover is one of the most important factors that may degrade the performance of TCP connections and real-time applications in wireless data networks. We proposed a seamless handover with Motion Prediction in IEEE 802.16e-based broadband wireless access networks. By intergrating MAC and network layer handovers efficiently, this scheme minimizes the handover delay and eliminates packet losses during handover Simulations show that this scheme achieves loss-free packet delivery without packet duplication and increases TCP throughput significantly.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.11
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• pp.2636-2656
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• 2013

To improve the cooperative efficiency of node cooperation and multiple access performance for multihop wireless networks, a priority-differentiated cooperative medium access control protocol with contention resolution (CRP-CMAC) is proposed. In the protocol, the helper selection process is divided into the priority differentiation phase and the contention resolution phase for the helpers with the same priority. A higher priority helper can choose an earlier minislot in the priority differentiation phase to send a busy tone. As a result, the protocol promptly selects all the highest priority helpers. The contention resolution phase of the same priority helpers consists of k round contention resolution procedures. The helpers that had sent the first busy tone and are now sending the longest busy tone can continue to the next round, and then the other helpers that sense the busy tone withdraw from the contention. Therefore, it can select the unique best helper from the highest priority helpers with high probability. A packet piggyback mechanism is also adopted to make the high data rate helper with packet to send transmit its data packets to its recipient without reservation. It can significantly decrease the reservation overhead and effectively improve the cooperation efficiency and channel utilization. Simulation results show that the maximum throughput of CRP-CMAC is 74%, 36.1% and 15% higher than those of the 802.11 DCF, CoopMACA and 2rcMAC protocols in a wireless local area network (WLAN) environment, and 82.6%, 37.6% and 46.3% higher in an ad hoc network environment, respectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.10
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• pp.1254-1260
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• 2019

Recently, 5G cellular systems have been attracted great attention as a key enabler for Industry 4.0. In this paper, we propose a novel random access based on pilot-assisted opportunistic transmission to support internet-of-things (IoT) scenario in cellular networks. A key feature of our proposed scheme is to enable each of IoT devices to attempt opportunistic transmission of its data packet in Step 3 with randomly selected uplink pilot signal. Both the opportunistic transmission and the pilot randomization in Step 3 are effective to significantly mitigate the occurrence of packet collisions. We mathematically analyze our proposed scheme in terms of packet collision probability and uplink resource efficiency. Through simulations, we verify the validity of our analysis and evaluate the performance of our proposed scheme. Numerical results show that our proposed scheme outperforms other competitive schemes.

• Journal of KIISE:Computing Practices and Letters
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• v.9 no.1
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• pp.47-59
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• 2003

The Internet telephony service is one of the commercially successful Internet application services. VoIP technology makes the service come true. VoIP deploys H.323 or SIP as the standard protocol for the distributed multimedia services over the Internet in which QoS is not guaranteed. VoIP carries the packetized voice over the RTP/UDP/IP protocol stack. The data transmission trouble is caused by UDP when the service is provided in private networks and some ISP-provided Internet access networks in the private address space. The Internet telephony users in such networks cannot listen the voices of the other parties in the public Internet or PSTN. Making the problem more difficult, the Internet telephony service considered in this paper gets the incoming voice packets of every session through only one UDP port number. In this paper, three schemes including the terminal proxy, the gateway proxy, and the protocol translation are suggested to solve the problems. The design and implementation of the NAT proxy server based on gateway proxy scheme are described in detail.

• Journal of KIISE:Information Networking
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• v.34 no.6
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• pp.525-532
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• 2007

Recently, broadband access networks have been competitively deployed all over the world with the development of various multimedia services for such a network. ETRI(Electronics and Telecommunications Research Institute) built the FTTH(Fiber-to-the-Home) service center to develop a next-generation equipment and a high-quality service/platform as well as to promote domestic industry in the field of optical communication. The FTTH service center has a variety of test equipments such as FTTH standard testbed for a BMT(Bench Mark Test), a network operation center, and IPTV service equipments. Also, ETRI deployed a new type of commercial optical access networks cooperating with ISP(Internet service provider). In this paper, we analyzed the quality degradation appeared in QoE(Quality of Experience), when IP data broadcasted from the FTTH service center is transmitted to subscribers through the commercial optical access network. Moreover, we proposed a noble solution to address this problem.

• Journal of Internet Computing and Services
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• v.8 no.5
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• pp.133-140
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• 2007

Currently, as the requirement for high quality Internet access from anywhere at anytime is consistently increasing, the interconnection of pure ad hoc networks to fixed IP networks becomes increasingly important. Such integrated network, referred to as hybrid ad hoc networks, can be extended to many applications, including Sensor Networks, Home Networks, Telematics, and so on. We focus on some data communication problems of hybrid ad hoc networks, such as broadcasting and routing. In particular. power failure of mobile terminals is the most important factor since it affects the overall network lifetime. We propose an energy-efficient routing protocol based on clustering for hybrid ad hoc networks. By applying the index-based data broadcasting and selective tuning methods, the infra system performs the major operations related to clustering and routing on behalf of ad hoc nodes. The proposed scheme reduces power consumption as well as the cost of path discovery and maintenance, and the delay required to configure the route.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.162-167
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• 1999

ATM technology is well developed. Small-scale access node and edge switches are introduced in the network. Large scale ATM core switches are prepared for backbone application. Currently, Internet traffic is increasing so rapidly and we need to consider effective way of accommodating the volume of traffic. In the other hand, QoS and traffic engineering concept is required in the Internet services. Here, in this paper, two technologies are explained and suggested for integration of networks for future ATM based IP network.