• Journal of KIISE:Computer Systems and Theory
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• v.34 no.9
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• pp.435-444
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• 2007

Caching web pages is an important part of web infrastructures. The effects of caching service are even more pronounced for wireless infrastructures due to their limited bandwidth. Medium to large-scale infrastructures deploy a cluster of servers to solve the scalability problem and hot spot problem inherent in caching. In this paper we present scheduling scheme based on cache utilization in a wireless internet proxy server cluster environment. The proposed method uses cache utilization for distributing evenly client requests to a cluster of cache servers and solving hot spot problem. We have implemented our approach and performed various experiments using publicly available traces. Experimental results on a cluster of 16 cache servers demonstrate that the proposed hashing method gives 45% to 114% Performance improvement over other widely used methods while addressing the hot spot problem.

• The KIPS Transactions:PartA
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• v.9A no.3
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• pp.327-332
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• 2002

Conventional proxy web cache, which is generally used to caching server, is a content-copy based system. This method focuses on speeding up the phase delivery not improving the webserver performance. However, if immense clients attempt to connect the webserver simultaneously, the proxy web cache cannot achieve the desired result. In this paper, we propose the web accelerator called the SCALA-AX, whitch improves web server performance by accelerating the delivery contents. The SCALA-AX is built in the Linux-based kernel as a kernel modulo and works in combination with the conventional webserver program. The SCALA-AX speeds up the processing rate of the webserver, because it processes the requests using the kernel thread. The SCALA-AX also applies the well-developed cache algorithm to the processing, and thus it obtains the advantage of the caching server without installing additional hardware. A banchmarking test demonstrates that the SCALA-AX improves webserver performance by up to 500％ for content delivery.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.7
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• pp.1854-1873
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• 2012

Owing to its simplicity and flexibility, the session initiation protocol (SIP) has been widely adopted as a major session-management protocol for Internet telephony or Voice-over IP (VoIP) services. However, SIP has faced various types of security threats. Call-disruption attacks are some of the most severe threats they face, and can greatly inconvenience consumers. In this paper, we analyze such SIP call-disruption attacks, and propose a method for detecting and counteracting them by extending the SIP INFO method with authentication. Using the proposed method, both the target user and the SIP server can detect the existence of a call-disruption attack on a user and counteract the attack. We demonstrate the effectiveness of the proposed method from the viewpoint of computational complexity by configuring a test-bed with an Asterisk SIP proxy server and an SIP performance (SIPp) emulator.

• Journal of the Korea Convergence Society
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• v.2 no.4
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• pp.9-14
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• 2011

Phishing is an attack to theft an user's identity by masquerading the user or the device. The number of phishing victims are sharply increased due to wide spread use of smart phones and messenger programs. Smart phones can operate various wi-fi based apps besides typical voice call and SMS functions. Generally, the messenger program such as Kakao Talk or Nate On is consisted of client and server functions. Thus, the authentication between the client and the server is essential to communicate securely. In this paper, we propose the messenger authentication protocol safe against smart phone phishing. To protect communications among clients, the proposed method provides message encryption and authentication functions.

• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.310-312
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• 2005

무선 인터넷 프록시 서버 클러스터에서 부하 분산기는 사용자의 요청을 각 서버(호스트)로 분산시키는 역할을 한다. 리눅스 가상 서버(LVS: Linux Virtual Server)는 소프트웨어적으로 사용되는 부하 분산기로서 여러 가지 스케줄링 방식들을 가지고 있다. 그러나 부하 분산시에 서버(호스트)의 유동적인 부하 정보를 반영하지 못하는 단점이 있다. 이에 개선된 방식으로 서버의 동시 연결 개수에 따라 상한계(Upper Bound)와 하한계(Lower Bound)를 설정하고, 요청을 분산하는 동적 스케줄링(Dynamic Scheduling)이 존재한다. 그러나 사용자의 요청 컨텐츠에 따라 상한계와 하한계가 바뀔 수 있음에도 불구하고 이 값들이 고정되어 있다는 단점을 가진다. 본 논문에서는 호스트 부하 정보에 기반한 스케줄링 방식을 제안한다. 제안된 방식은 호스트의 부하 정보를 바탕으로 사용자의 요청을 분산하였으며, 사용자의 요청에 따라 상한계와 하한계가 바뀔 수 있음을 고려하여 상한계와 하한계를 설정하지 않고 사용자 요청 컨텐츠에 따라 적절하게 요청이 분배되도록 하였다. 16대의 컴퓨터를 사용하여 실험을 수행하였으며, 실험 결과 사용자가 요청하는 컨텐츠가 동일한 경우에는 기존 스케줄링 방식과 $13\%$ 성능 감소를 다른 경우에는 기존 스케줄링 방식보다 $102\%$의 성능 향상을 보임을 확인하였다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.6
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• pp.1-16
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• 2012

In this paper, we propose a cost-effective location and service management scheme in LTE (Long Term Evolution) networks, which a per-user service proxy is created to serve as a gateway between the mobile user and all client-server applications engaged by the mobile user. The service proxy is always co-located with the mobile user's location database such that whenever the MU's location database moves during a location hand-off, a service hand-off also ensues to co-locate the service proxy with the location database. This allows the proxy to know the location of the mobile user all the time to reduce the network communication cost for service delivery. We analyze four integrated location and service management schemes. Our results show that the centralized scheme performs the best when the mobile user's SMR (service to mobility ratio) is low and ${\upsilon}$(session to mobility ratio) is high, while the fully distributed scheme performs the best when both SMR and ${\upsilon}$ are high. In all other conditions, the dynamic anchor scheme is the best except when the service context transfer cost is high under which the static anchor scheme performs the best. Through analytical results, we demonstrate that different users with vastly different mobility and service patterns should adopt different integrated location and service management methods to optimize system performance.

• Journal of KIISE:Information Networking
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• v.37 no.6
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• pp.459-465
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• 2010

Mobile IPv6(MIPv6) features have several defects such as overloading of nodes, loss of wireless signals, packet loss, movement problem and so forth. Proxy Mobile IPv6 (PMIPv6) got over the limit of MIPv6 problems. MIPv6 features have several defects such as overloading of nodes, loss of wireless signals, packet loss, movement problem and so forth. Research on PMIPv6, which features network-based mobility is actively in progress in order to resolve these issues. PMIPv6 is emerging as a new paradigm that can overcome the limitations of the existing MIPv6. Nevertheless, such PMIPv6 also incurs problems during hand-over. While it offers a solution to node-based problems, it does, too, create long delay times during hand-over. Since MN (Mobile Node) has been sensing its own movements on MIPv6, fast handover can be done easily. However it can't apply fast handover like MIPv6, as it can't apply fast handover like MIPv6 In this paper, the author solved hand-over problem on MIPv6. MAG knows location information of MN and if MN moves into other MAG's area, Location Server gives MN information to the MAG. Therefore, this mechanism makes hand-over process easier.

• The KIPS Transactions:PartC
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• v.13C no.6 s.109
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• pp.785-794
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• 2006

Nowadays, Internet is used worldwide and network traffic is increasing dramatically. Much of Internet traffic is due to the web applications. And I propose a new cooperative web caching scheme, called DCOORD which tries to minimize the overall cost of Web caching. DCOORD reduces the communication cost by coordinating the objects which are cached at each cache server. In this paper, I compare the Performance of DCOORD with two well-known cooperative Web caching schemes, ICP and CARP, using trace driven simulation. In order to reflect the cost factor in the network communication, I used the CSR(Cost-Saving Ratio) as our performance metric, instead of the traditional hit ratio. The performance evaluations show that DCOORD is more cost effective than ICP and CARP.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.2
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• pp.86-94
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• 2010

This paper proposed an authentication interworking protocol (AIP) based on IEEE 802.21 MIH in the heterogeneous networks. The proposed AIP using the RSA signature reduces handover delay time and communication message overhead when the mobile node moves between the heterogeneous networks. It defines new AIP TLV in MIH frame format and uses the MIH Information Server (MIHIS) for proxy signature issue instead of the authentication server for the heterogeneous networks. For low handover delay, the proposed AIP performs pre-authentication processes with MIH protocol before layer 2 handover. Also, this paper analyzed the performance of the handover and compared with the non-secure MIH protocol.

• The Journal of the Korea Contents Association
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• v.6 no.12
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• pp.169-176
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• 2006

Since home network system is usually set up based on the built-in system inside home at the time of construction, it has a difficulty in being compatible with new devices after construction. In this paper, we propose DBS(Dynamic Binding System) that can make links effectively among the devices located in inside and outside of home networks. Implementation of the DBS is based on the ZigBee's binding in WPAN(Wireless Personal Area Network). For this research, we constructed the system consisting of home server that contains proxy server and location server, devices inside home in which tinyOS is embedded, and mobile device that is an emulator. The communication inside home is done by IEEE 802.15.4 protocol and the communication between servers and mobile devices outside home is done by TCP/IP protocol. Regardless of device's address format, the DBS facilitates a link among the devices located inside and outside of home networks. And, introducing a new device into home network can be recognized easily by exchanging messages between devices.