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Protecting Download Traffic from Upload Traffic over Asymmetric Wireless Links
Kim, Hwangnam,Lee, Woonghee,Kim, Hyunsoon,Kim, Hwantae,Yang, Jaehyeuk Michael WILEY INTERSCIENCE 2018 WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Vol.2018 No.-
<P>Many varied mobile device networks have been developed with the advancement of communication and network technologies. Cellular data networks are currently the most widely used, and the number of cellular network subscriptions has increased steadily. Most recent wireless access technologies employ asymmetric uplinks and downlinks because mobile subscribers usually download contents from the Internet. Therefore, most cellular network service providers allocate more bandwidth to downlinks than uplinks for mobile subscribers. However, this asymmetry can have unexpected influence on network performance, particularly TCP performance. When the uplink interface is congested, TCP ACK packets are delayed by TCP data packets on the uplink, causing considerable TCP retransmissions on the downlink channel. Thus, downlink bandwidth cannot be fully utilized, which results in significantly degraded downlink throughput. To resolve this problem, this paper proposes a feedback scheme, network traffic chunk regulator (NCR). We analyzed the aforementioned problem through the empirical study, and we designed and implemented NCR based on the analysis. NCR adaptively controls TCP according to the degree of link usage asymmetry. We evaluate NCR performance through simulations and experiments with real devices. We verify that the proposed scheme allows the downlink traffic to not interfere with the aggressive uplink traffic. Thus, NCR increases total link utilization and aggregated throughput significantly, without imposing additional overhead on base or mobile stations.</P>
Wi-Fi Seeker: A link and Load Aware AP Selection Algorithm
Kim, Hyunsoon,Lee, Woonghee,Bae, Mungyu,Kim, Hwangnam IEEE Computer Society 2017 IEEE TRANSACTIONS ON MOBILE COMPUTING Vol.16 No.8
<P>The demand of mobile traffic increases tremendously as various Internet services are provided to mobile phones and computing devices, making mobile carriers increase the capacity of their cellular network. Since current cell towers and auxiliary devices cannot carry an excessive amount of traffic, several mobile carriers try to install low cost wireless equipment such as a Wi-Fi access point (AP) in order to offload overloaded traffic on cell towers. However, APs are installed randomly unlike cell towers because they can be installed by anyone and anywhere. The randomized allocation of APs incurs interference that causes serious degradation of wireless communication quality. Therefore, it is necessary to design mobile devices to use the environment or channel that contains the least interference for proper Wi-Fi communication. In order to make a mobile device experience the best wireless download quality, this paper proposes a novel AP selection mechanism that selects an AP that contains the least interference level compared to others with different number of communicating devices and amount of traffic load. The proposed selection mechanism does not require any additional feedback from nearby devices or APs. Performance evaluation was done by using real mobile devices with open source platform called Android.</P>
Adaptive Decision of Wireless Access Network for Higher User Satisfaction
Kim, Hyunsoon,Bae, Mungyu,Lee, Woonghee,Kim, Hwangnam WILEY INTERSCIENCE 2018 WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Vol.2018 No.-
<P>Today’s mobile devices mostly contain more than one wireless interface for Internet connection. Smartphones mostly have both LTE and Wi-Fi for data communication through Internet. Although the availability of Wi-Fi is incomparable to that of cellular network, its strength lies in the low cost and high data rate due to continuous PHY and MAC advancement of 802.11 protocol extensions. In this paper, we propose a device-centric system that performs cost-effective network connectivity to the mobile device by selectively activating Wi-Fi communication according to the device mobility and corresponding history of Wi-Fi usage. By analyzing the device mobility using attached sensors, the system selects appropriate Wi-Fi that has been often used in that mobility state. The system was implemented in actual mobile devices that were used to several experiments we designed to prove high performance of the system.</P>
객체지향 DBMS를 위한 메모리내 객체 관리기의 설계와 구현
김황남(Hwangnam Kim),차재혁(Jaehyuk Cha),이석호(Sukho Lee) 한국정보과학회 1995 정보과학회논문지(B) Vol.22 No.9
객체중심 DBMS에서 빠른 디스크 입출력을 위한 저장 서브시스템의 데이타 구조는 데이터베이스 연산의 효율적인 수행을 지원하기 어려우므로 별도의 메모리내 객체 구조가 필요하다. 또 메모리에 적재된 객체를 메모리 포인터를 통해 접근할 때 허상 참조(dangling reference)문제가 발생할 수 있다. 따라서 본 논문에서는 메모리내 객체 구조와 저장 데이타 구조 사이에 존재하는 불일치와 허상 참조 문제를 해결하는 메모리내 객체 관리기를 제안한다. 본 시스템은 저장 데이타 구조를 메모리내 객체 구조로 변환하고, 이를 객체 버퍼 내에 관리한다. 그리고 연산 인터페이스를 제공하므로써 허상 참조 문제를 해결하고 저장 서브시스템과 객체중심 모델을 지원하는 상위 서브시스템 사이에서 인터페이스 역할을 한다. In an object-oriented DBMS, the disk format of an object in a storage subsystem cannot support the execution of database operations efficiently, since they are designed for the fast disk I/O. So there is a need for in-memory format of an object Also, the dangling reference problem occurs in accessing in-memory objects by the memory pointer. Therefore this paper proposes an in-memory object manager that solves not only the difference between the in-memory object structure and the stored data structure, but also the dangling reference problem. The proposed system transforms from the stored data to the in-memory objects. and maintains the latter within the object buffer. It also solves the dangling reference problem by the operational interfaces This services the upper subsystems supporting the model as the interface of the storage system.
멀티미디어 DBMS를 위한 메모리내 객체 관리기의 설계와 구현
김황남(Hwangnam Kim),박한묵(Hanmook Park),차재혁(Jaehyuk Cha),이석호(Sukho Lee) 한국정보과학회 1993 한국정보과학회 학술발표논문집 Vol.20 No.2
본 논문은 메모리내 객체 관리기의 설계와 구현을 다룬다. 이 시스템은 멀티미디어 데이타베이스 관리 시스템인 ALPHA에서 메모리내에 위치하는 객체를 관리하는 모듈로 입출력 성능과 연산효율 개선을 위해 설계되었다. 시스템 내부에 객체 버퍼를 두어 메모리내 형식의 객체를 유지하고 객체 버퍼를 사용할 때 발생할 수 있는 오류를 막기 위하여 연산 인터페이스를 두고 있다. 그리고 대용량 데이타를 처리하기 위해서 대용량 데이타의 부분을 정의하여 처리할 수 있도록 했다.