• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5B
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• pp.475-488
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• 2003

To prevent performance degradation of TCP due to packet losses in the smooth handoff by the route optimization extension of Mobile IP protocol, a buffering of packets at a base station is needed. A buffering of packets at a base station recovers those packets dropped during handoff by forwarding buffered packets at the old base station to the mobile user. But, when the mobile user moves to a congested base station in a new foreign subnetwork, those buffered packets forwarded by the old base station are dropped and TCP transmission performance of a mobile user in the congested base station degrades due to increased congestion by those forwarded burst packets. In this paper, considering the general case that a mobile user moves to a congested base station, we analyze the influence of packet buffering on TCP performance according to handoff arrival distribution for Drop-tail and RED (Random Early Detection) buffer management schemes. Simulation results show that RED scheme can reduce the congestion increased by those forwarded burst packets comparing Drop-Tail, but RED scheme cannot avoid Global Synchronization due to forwarded burst packets by the old base station and new buffer management scheme to avoid it is needed in Mobile IP based networks.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.684-685
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• 2013

p-형 반도체인 Cu(In,Ga)$Se_2$ (CIGS) 광 흡수 층은 이보다 에너지 밴드 간격이 큰 n-형 반도체와 이종 접합을 형성한다. 흡수층과 윈도우층 사이의 결정구조 차이와 밴드갭 에너지 차이를 완화시키기 위해 버퍼층이 필요하다. 버퍼층을 형성하는 물질로 화학적 용액 성장법(Chemical Bath deposition)을 사용한 CdS가 많이 적용되어 왔으나 Cd의 유해성 및 습식 공정으로 인한 연속공정에 대한 어려움이 있다. 따라서 버퍼층을 Cd을 포함하지 않는 ZnS, $In_2S_3$, (Zn, Mg)O 등과 같은 물질로 대체하여 원자층 증착법(Atomic Layer Deposition), 펄스레이져증착법(Pulsed Laser Deposition), 스퍼터링(sputtering) 등과 같은 건식으로 성장시키는 연구가 활발히 진행되고 있다. 본 연구에서는 $ZnO_{1-x}S_x$ ($0.2{\leq}x{\leq}0.4$)를 반응성 스퍼터링으로 증착하여 큰 밴드갭 에너지와 높은 광투과율를 갖는 버퍼층을 제작하였다. CIGS 박막의 손상을 줄여주기 위하여 RF 파워는 240, 200, 150, 100 W로 변화시켰다. CIGS 태양전지의 I-V 측정 결과, RF 파워가 150 W일 때 10.7%의 가장 높은 변환 효율을 보였고, 150 W 이상에서는 파워가 증가할 때 단락전류는 감소하였으며 개방전압은 다소 증가하였다. 반면 100 W에서 단락전류는 다소 증가하는 것에 반해 개방 전압이 급격히 낮아졌다. 이것은 파워에 따라 결합되는 산소의 양이 다르기 때문으로 생각된다.

• Journal of Broadcast Engineering
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• v.16 no.5
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• pp.722-737
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• 2011

In this paper, we propose an estimation of network jitter that occurs when transmitting TCP packets containing MPEG-2 TS in progressive streaming service over wired or wireless Internet networks. Based on the estimated network jitter size, we can calculate required de-jitter buffering time to absorb the network jitter at the receiver side. For this purpose, by exploiting the PCR timestamp existing in the TS packet header, we create a new timestamp information that is marked in the optional field of TCP packet header to estimate the network jitter. By using the proposed de-jitter buffering scheme, it is possible to employ the conventional T-STD buffer model without any modification in the progressive streaming service over IP networks. The proposed method can be applicable to the recently developed international standard, MPEG DASH (dynamic adaptive streaming over HTTP) technology.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.1
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• pp.69-76
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• 2014

In this paper, we propose a buffering scheme to improve the performance in P2P live streaming systems by adjusting the ratio of caching and prefetching portion of each peer. To this end, we assign all the peers into many groups depending on their playback periods. We then determine the ratio of caching and prefetching portion in each peer depending on its playback time position relative to those of other peers within the same group. In other words, as the playback position of a peer gets later, we increase the ratio of its caching portion. On the contrary, as the playback position of a peer gets eariler, we increase the ratio of its prefetching portion. This can significantly increase the degree of data duplication among peers that belong to each specific group. By simulation experiments, we show that our proposed an integrated prefetching/caching scheme can improve the performance considerably in terms of jitter ratio, initial playback delay and shared buffermap ratio when compared to the existing fixed portion buffering scheme.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.256-258
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• 2001

이동 환경에서의 서비스가 대중화 되면서 문제가 되고 있는 것이 바로 이동 호스트의 전력 제어 문제이다. 이동 호스트는 충분한 전력을 얻기 힘들기 때문에 데이터 전송을 받지 않는 경우에는 최소한의 정보만을 교환하는 상태로의 전의가 필수적이다. 현재 IETF의 Seamoby Working Group에서 논의되고 있는 IP 페이징 프로토콜의 경우에는 요구사항과 논리적인 구조만이 정의되어 있다. 현재 정의되어 있는 구조의 문제점은 유휴 (formant) 모드에 있는 이동 호스트에 데이터를 전송하기 위해서는 Dormant Monitoring Agent(DMA)로 전송된 데이터에 대하여 버퍼링이 수행되어야만 한다. 버퍼링의 목적은 이동 호스트의 유휴 모드에서 활성 (active) 모드로 전의 되는 시간 동안의 데이터의 손실을 방지하기 위함이다. 따라서, 하나의 DMA해서 관리해야 하는 이동 호스트가 많은 경우에는 대회의 양이 문제가 된다. 즉, 확장성 문제점이 존재하게 된다. 본 논문은 이러한 문제점을 줄이기 위하여 Domain Name Server(DNS)를 이용한 IP 페이징 제공 방안을 제안한다. 본 메커니즘은 송신자가 DNS에 호스트의 IP주소를 얻고자 하는 경우 IP 페이징 프로토콜을 먼저 이동 호스트의 페이징 에이전트에 전송함으로써 미리 이동 호스트를 활성 모드로 변경하게 함으로써 이전 메커니즘에서 적용되어야 하는 버퍼의 크기를 줄일 수 있는 메커니즘이다.

• Proceedings of the Korea Information Processing Society Conference
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• 2000.10b
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• pp.1099-1102
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• 2000

입출력버퍼형 스위치를 위한 간단한 셀 스케줄링 알고리즘을 제시한다. 스위치는 고속동작 및 성능 향상을 위해 이중 스위칭 플랜을 갖고 있다. 제안한 알고리즘은 각각의 스위칭 플랜에서 독립적으로 수행되며 전송요청 (request), 전송허가(grant). 전송확정 (accept)의 3 단계 동작으로 이루어져 있다. 또한 각 3 단계동작을 한 셀시간에 한 번씩만 수행하여 단위 셀시간이 작은 고속 스위칭에 적합하다. 모의실험 결과 제안한 알고리즘의 성능이 Bernoulli 트래픽 입력에 대해 출력버퍼형 스위치의 성능과 거의 동일하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.772-775
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• 2004

After Morris' Internet Worm in 1988, the stack buffer overflow hacking became generally known to hackers and it has been used to attack systems and servers very frequently. Recently, many researches tried to prevent it, and several solutions were developed such as Libsafe and StackGuard; however, these solutions have a few problems. In this paper we present a new stack buffer overflow attack prevention technique that uses the system call monitoring mechanism and memory address where the system call is made.

• The KIPS Transactions:PartC
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• v.13C no.7 s.110
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• pp.821-830
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• 2006

As internet worms are spread out worldwide, the detection and filtering of worms becomes one of hot issues in the internet security. As one of implementation methods to detect worms, the Linux Netfilter kernel module can be used. Its basic operation for worm detection is a string matching where coming packet(s) on the network is/are compared with predefined worm signatures(patterns). A worm can appear in a packet or in two (or more) succeeding packets where some part of worm is in the first packet and its remaining part is in its succeeding packet(s). Assuming that the maximum length of a worm pattern is less than 1024 bytes, we need to perform a string matching up to two succeeding packets of 2048 bytes. To do so, Linux Netfilter keeps the previous packet in buffer and performs matching with a combined 2048 byte string of the buffered packet and current packet. As the number of concurrent connections to be handled in the worm detection system increases, the total size of buffer (memory) increases and string matching speed becomes low In this paper, to reduce the memory buffer size and get higher speed of string matching, we propose a string matching scheme without using buffer. The proposed scheme keeps the partial matching result of the previous packet with signatures and has no buffering for previous packet. The partial matching information is used to detect a worm in the two succeeding packets. We implemented the proposed scheme by modifying the Linux Netfilter. Then we compared the modified Linux Netfilter module with the original Linux Netfilter module. Experimental results show that the proposed scheme has 25% lower memory usage and 54% higher speed compared to the original scheme.

• Journal of KIISE:Information Networking
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• v.28 no.2
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• pp.242-250
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• 2001

This paper deals with the TCP bandwidth guarantee problem in a differentiated serviccs(Diffserv) network. The Diffserv assured s<:rvice differentiates packet drop probabilities to guarantee the promised bandwidth even under network congestion. However a token buffer marker fails to show adequate performance because TCI' generates packets according to the unique Tel' congestion control mechanism. We propose a marker that uses a data buffer as well as a token buffer. The marker with a data buffer works well with the assured service mechanism because it smooths Tel' traffic. We showed that the marker with a data buffer achieves the target throughput better than a marker with a token buffer only. We also showed that the optimal buffer size is proportional to reserved throughput and HTT.

• Journal of Korea Multimedia Society
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• v.8 no.2
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• pp.249-257
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• 2005

This paper aims at reducing aliasing in pixel-based rendering for 3D implicit surfaces by shifted multi Z-buffers. The voxelized implicit surfaces with high resolution take so much time in generating high Quality image without aliasing. So in rendering a voxelized implicit surfaces, a new antialiasing method which can generate a high quality image at a lower resolution is required. Therefore, this paper suggests that a method which get various sampling values by shifting several z-buffers in each voxel and average them, The advantages are effective memory, simple calculation and easy convergence with various filters. But, the increase of number of z-buffer also increase the consuming time rapidly. Therefore, the research for representing the relation the degree of image quality with the consumption of time as a number is required.