• The Journal of Korean Association of Computer Education
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• v.15 no.5
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• pp.55-62
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• 2012

With the development of mobile communications and Internet technology, there is a strong need to provide seamless and fast connectivity for roaming devices. Generally, the mobile host (MH) may have several available networks when entering a new wireless area. However, the standard of decision for user's internet connection is provided only the subsystem identification (SSID) and signal strength of access point (AP). These two standards could not enough to decide optimal AP to the MH. Therefore, to decide the optimal AP, more information is needed. In this paper, we present additional information such as status of MH, capacity, current load, and depth of network hierarchy, by router advertisement message at layer 3. Also, we proposed decision engine (DE) on the MH that analyzes APs and decides the optimal AP automatically by AP's status information. For the MH, wireless connection period is increased, the power consumption is decreased, and the signaling overhead is reduced. For AP and router, the load balancing is provided and the network topology can also be more efficient.

• The KIPS Transactions:PartC
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• v.14C no.1 s.111
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• pp.55-64
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• 2007

Behind the popularity of VoIP in these days, it may present significant security challenges in privacy and accounting. Authentication and message encryption are considered to be essential mechanisms in VoIP to be comparable to PSTN. SIP is responsible for setting up a secure call in VoIP. SIP employs TLS, DTLS or IPSec combined with TCP, UDP or SCTP as a security protocol in VoIP. These security mechanisms may introduce additional overheads into the SIP performance. However, this overhead has not been understood in detail by the community. In this paper we present the effect of the security protocol on the performance of SIP by comparing the call setup delays among security protocols. We implement a simulation of the various combinations of three security protocols and three transport layer protocols suggested for SIP. UDP with any combination of security protocols performs a lot better than the combination of TCP. TLS over SCTP may impose higher impact on the performance in average because TLS might have to open secure channels as the same number of streams in SCTP. The reasons for differences in the SIP performances are given.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.12
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• pp.1148-1159
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• 2012

It is of great significance in the NGN - which supports a ubiquitous network environment in which users can use multiple devices and all the devices are connected to networks - to support the terminal mobility as well as service continuity. The IMS architecture, which is considered as session control layer in the NGN, exists to support a wide range of advanced new services in addition to the traditional voice and data connectivity offerings of "old" telecommunications. The recent IMS specification also defines IUT (Inter UE Session Transfer) functionality in order to support service continuity in the NGN. However, service continuity in IMS has a limitation that two terminals involved in session transfer should belong to the same user. In this paper, we proposed a new device discovery mechanism for IMS and extended UEs with a few capabilities to overcome some of IMS's limitations. We also analysed how much overhead of the proposed method in terms of signaling cost will be.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11B
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• pp.968-980
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• 2008

Providing handover with guaranteed QoS for real-time multimedia service such as VoIP, video/audio streaming, and video conferencing in wireless LAN is a challenging task. In this paper, we present efficient layer 2 handover mechanism in wireless LAN, which can provide fast handover with guaranteed QoS for real-time multimedia service. To this end, the scanning period and the number of channels per scanning for handover are dynamically adapted to the type of applications and wireless networking environment, so that both the degradation of application service quality and signaling overhead are minimized simultaneously. The performance of the proposed mechanism is verified by the simulation. The simulation results show that the proposed mechanism guarantess QoS of each multimedia application with minimal power consumption.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.2
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• pp.687-708
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• 2017

The machine-to-machine (M2M) communication is featured by tremendous number of devices, small data transmission, and large uplink to downlink traffic ratio. The massive access requests generated by M2M devices would result in the current medium access control (MAC) protocol in LTE/LTE-A networks suffering from physical random access channel (PRACH) overload, high signaling overhead, and resource underutilization. As such, fairness should be carefully considered when M2M traffic coexists with human-to-human (H2H) traffic. To tackle these problems, we propose an adaptive Slotted ALOHA (S-ALOHA) and time division multiple access (TDMA) hybrid protocol. In particular, the proposed hybrid protocol divides the reserved uplink resource blocks (RBs) in a transmission cycle into the S-ALOHA part for M2M traffic with small-size packets and the TDMA part for H2H traffic with large-size packets. Adaptive resource allocation and access class barring (ACB) are exploited and optimized to maximize the channel utility with fairness constraint. Moreover, an upper performance bound for the proposed hybrid protocol is provided by performing the system equilibrium analysis. Simulation results demonstrate that, compared with pure S-ALOHA and pure TDMA protocol under a target fairness constraint of 0.9, our proposed hybrid protocol can improve the capacity by at least 9.44% when ${\lambda}_1:{\lambda}_2=1:1$and by at least 20.53% when ${\lambda}_1:{\lambda}_2=10:1$, where ${\lambda}_1,{\lambda}_2$ are traffic arrival rates of M2M and H2H traffic, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.12C
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• pp.1245-1250
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• 2002

For recent years, the environment of use on internet has been changed from the wired internet access to the wireless internet access increasingly, and the use of real time application data has been increased. Therefore the research and evolution of wireless network for providing of user's mobility and QoS at the same time must be essential. IETF already proposed Mobile IPv6 for providing mobility and RSVP for QoS through resource reservation. These future are expected to be used not only wired network but also wireless network. But there are not yet proposed the integration and efficient interworking of two mechanism. For the solution of problem on efficient interworking issue, for instance signaling overhead and reservation delay increasing due to often handoff, this paper first proposed to use of IETF Cellular IP based on Mobile IPv6 for wireless network model with fast mobility and a improved RSVP mechanism using the flow label field in IPv6 header.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.5
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• pp.107-119
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• 2013

This paper reinforced security under the network evaluation of wire wireless integration of NEMO (NEwork MObility) supporting mobility and network-based PMIPv6 (Proxy Mobile IPv6). It also proposes $SK-L^2AS$ (Symmetric Key-Based Local-Lighted Authentication Scheme) based on simple key which reduces code calculation and authentication delay costs. Moreover, fast handover technique was also adopted to reduce handover delay time in PMIPv6 and X-FPMIPv6 (eXtension of Fast Handover for PMIPv6) was used to support global mobility. In addition, AX-FPMIPv6 (Authentication eXtension of Fast Handover for PMIPv6) is proposed which integrated $SK-L^2AS$ and X-FPMIPv6 by applying Piggybacks method to reduce the overhead of authentication and signaling. The AX-FPMIPv6 technique suggested in this paper shows that this technique is better than the existing schemes in authentication and handover delay according to the performance analysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6C
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• pp.512-522
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• 2005

In this paper, an optimal determination method of the subband-frame size and mode-switching level is proposed for adaptive OFDM-TDD systems in frequency-selective time-varying channels. The optimization problem considering frequency selectivity. user's mobility, and the signaling overhead caused by the mode change information is formulated in the maximum spectral efficiency sense satisfying the target BER. Assuming that subband-frame size is given, the mode-switching level is first optimized so that the spectral efficiency can be maximized satisfying the target BER. The subband-frame size among candidates is then determined, which maximizes the spectral efficiency. Simulation results show that the proposed scheme outperforms conventional schemes, in terms of the spectral efficiency and the BER.

• Journal of the Korea Society of Computer and Information
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• v.12 no.5
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• pp.139-144
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• 2007

The mobile terminal's frequent changes to the access point introduce significant network overhead in mobile IP networks. To solve this problem, we introduce a hierarchical structure with consideration given to the dynamic value of neighbor scope in IP regional registration[1]. When a mobile terminal moves within the neighbor given by the scope value, it makes registration locally without registration with its home agent. We analyze the algorithm mathematically and show the numerical results. As a result, optimization of the scope value for the localized registration under the hierarchical structure makes the proposed scheme outperform the standard mobile IP protocol[2]. This can be explained from the fact that there is only local registration for terminal's movement within the scope region. Moreover, as the signaling cost for home agent increases, the proposed scheme becomes more advantageous.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.4
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• pp.337-349
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• 2013

In this paper, we propose a new mobility management scheme, called i-FP(intelligent Fast PMIPv6). Our proposed i-FP scheme is addressed for solving the existing local mobility management problems from legacy frameworks. To move MN(Mobile Node) to other networks in one domain, i-FP employs three network entities which are extended from PMIPv6(Proxy Mobile IPv6), LMA(Local Mobility Anchor), MAG(Mobile Access Gateway) and MN. In i-FP, the three network entities can reduce the handover delay time of MNs. Also, i-FP uses an IP header swapping mechanism to avoid the traffic overhead and improve the throughput of network. To evaluate the performance of i-FP, we analyze our i-FP, HMIPv6(Hierarchical Mobile IPv6) and PMIPv6 which are legacy protocols of local mobility management in terms of various parameters. Finally, our i-FP scheme shows good performance(reduction of routing hops 10.2%, signaling costs 58.5% and handover delay 16.3%) than other network schemes for the total cost.