• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.2B
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• pp.124-132
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• 2007

Where a wireless LAN and a cellular network coexist, a mobile node has to experience vertical handoffs to move between them. Immediately after the vertical handoffs, TCP must need adaptation latency to adjust its congestion window to the proper size at a newly arrived network to use full of a new end-to-end available bandwidth. Even though SACK TCP has the best performance among other regular TCPs in the previous studies, it still cannot use full of the new available bandwidth quickly due to its inefficient increasing way of congestion window. BIC TCP, that becomes a popular TCP in long fat networks, has great feature working well against vertical handoffs by increasing congestion window exponentially with TCP connection sustained. In this paper, we derive adaptation latency of SACK TCP and BIC TCP numerically, and verify them by simulations. We also find that the shorter adaptation latency of BIC TCP produces higher throughput than SACK TCP on vertical handoffs. Consequently, to get higher performance on vertical handoff situations, we propose to use BIC TCP.

• Journal of Internet Computing and Services
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• v.7 no.5
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• pp.43-57
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• 2006

Next-generation mobile communication systems evolve in the form of high speed data transmission along with integration of wired-wireless network. Therefore, it needs researches on integrating service to heterogeneous networks to offer high speed data transmission and various services while supporting user mobility. In existing studies, heterogeneous networks are linked to single core network separatively, Since vertical handoff between heterogeneous networks leads to some delay, packets may be lost during vertical handoff. To solve this problem, this paper proposes an hierarchically integrated network architecture considering the characteristics of CDMA2000, WiBro, and WLAN. The hierarchically integrated networks are overlaid according to coverage of each network. Therefore, the proposed architecture can minimize handoff delay and packet loss. In addition, this paper proposes an integrated framework for next generation mobile communication networks.

• The KIPS Transactions:PartB
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• v.12B no.6 s.102
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• pp.679-684
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• 2005

There are a few representative wireless network access technologies used widely. WWAN is celluar based telecommunication networks supporting high mobility, WLAN ensures high data rate within hotspot coverage, and WDMB support both data and broadcasting services correspondingly. However, these technologies include some limitations especially on the mobility, data rate, transmission direction, and so on. In order to overvome these limitations, there are various studies have been proposed in terms of 'Vortical Handoff' that offers seamless connectivity by switching active connection to the appropriate interface which installed in the mobile devices. In this paper, we propose the interface selection algorithm and network architecture to maximize the life time of entire system by minimizing the unnecessary energy consumption of another interfaces such as WLAN, WDMB that are taken in the user equipment. In addition, by using the results of analyzing multiple types of traffic and managing user buffer as a metric for vertical handoff, we show that the energy efficiency of our scheme is $75\%$ and $34\%$ than typical WLAN for WDMB and WLAN preferred schemes, correspondingly.

• Journal of KIISE:Information Networking
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• v.32 no.2
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• pp.203-214
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• 2005

The integration of 3G networks and WLANs as complementary has been begun to attract much attention in industry as well as academia. This topic is becoming a burning issue, and one of the key questions which it raises is how to support a seamless vertical handoff. This paper introduces a new network interface selection algorithm for energy-efficient vertical handoff in tightly coupled systems capable of supporting seamless handoff. Our proposed scheme, Wise Interface Selection (WISE) switches the active network interface, after taking into consideration the characteristics of the network interface cards and the current level of data traffic, with the cooperation of the mobile terminals and network. Network interface switching operates independently on both the downlink and the uplink for the purpose of energy conservation. We show through simulation that less energy is consumed with WISE than when only a 3G network or WLAN interface is used, resulting in a longer lifetime for the mobile terminals. In the case of TCP connections, additional throughput gain can also be obtained.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2006.07a
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• pp.735-735
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• 2006

• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.58-60
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• 2004

차세대 네트워크의 출현으로 다양한 형태의 통신망 들 간의 융합이 중요해졌다. 무선 망의 경우 이질적인 망들 간의 통합 및 융합이 이루어지기 위해서는 끊김 없는 이동성 지원이 매우 중요하다. 끊김 없는 이동성 지원은 이질적인 무선망 간의 이동시에도 지속적으로 세션을 유지하는 기능을 말한다. 이러한 기능을 핸드오프 기법이라 하며 현재 다양한 연구가 진행 중이다. 본 논문에서는 현재 제안되어 있는 핸드오프 기법 중 USHA(Universal Seamless Handoff Architecture)를 기반으로 하여 적용하기 쉬우며 확장성과 신뢰성을 보장하는 핸드오프 모델을 제안한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2006.05a
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• pp.1049-1052
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• 2006

차세대의 무선 네트워크 기술은 기존의 망을 통합하고 IP화 하는 방향으로 발전중이며, WWAN과 WLAN의 통합망에 관한 연구가 활발히 진행 중이다. 본 연구는 최근 상용화 서비스가 이루어지고 있는 WDMB 기술을 WWAN, WLAN과 강결합(Tight Coupling) 방식으로 통합한 네트워크 환경을 제안한다. 본 연구에서 제안하는 수직적 핸드오프(Vertical Handoff) 기법은 WLAN 인터페이스를 필요한 상황에만 구동하여 에너지 소모율을 낮춘다. 또한 WDMB 인터페이스를 상시 구동하여 데이터 트래픽이 발생할 때에 곧바로 WDMB 인터페이스를 통해 데이터 전송을 시작하여 전송률을 높인다. 또한 성능 평가를 통하여 단말에 장착된 모든 인터페이스를 구동하는 방식과 비교하여 에너지 소모율이 경감되었으며, 단말에 장착된 한 가지 인터페이스만을 구동하는 방식과의 비교를 통해 데이터 전송률이 크게 향상되었음을 보인다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.8
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• pp.597-606
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• 2013

The performance of TCP depends on the degree of traffic congestion between the sender and the receiver. The traffic could increase, and this causes congestion which may cause trouble in data transfer. Then, TCP tries to eliminate the trouble by reducing the transfer speed with slowstart scheme. When a mobile node moves over heterogeneous wireless networks, TCP experiences dramatic change of the amount of traffic, and it performs slowstart. In this paper, we propose the efficient scheme of TCP slowstart that should performs after vertical handoff. In this scheme, TCP receiver forces slowstart, which is different form normal schemes. Its performance is better than the normal schemes in that TCP sender experiences traffic congestion and performs slowstart. We perform simulation to measure and to verify the improved performance.

• 한국ITS학회:학술대회논문집
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• 2005.11a
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• pp.173-176
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• 2005

• Proceedings of the Korean Information Science Society Conference
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• 2004.10a
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• pp.700-702
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• 2004

MS(Mobile Station)가 HSDPA(High Speed Downlink Packet Access)를 지원하는 W-CDMA(Wideband Code Division Multiple Access)망과 IEEE 802.16e를 지원하는 HPi(High Speed Portable Internet)망 사이를 이동할 때 발생하는 vertical 핸드오프 시 MS는 이전 경로 상에서 받지 못한 데이터를 새로운 경로로 넘겨받아 데이터가 순서대로 손실 없이 착신됨을 보장받아야 한다. 이것은 재전송의 오버헤드를 줄이는 이점이 있다. 또한 vertical 핸드오프 시 새로운 망에 MS가 재구성되어지는 과정이 포함되어야 한다. 이를 위해 본 논문에서는 vertical 핸드오프 시 이전 경로 상에서 받지 못한 데이터를 순서대로 넘겨받는 것과 새로운 망에 적용되는 MS 재구성에 관련된 프로토콜을 제안한다.