• Journal of Communications and Networks
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• v.18 no.2
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• pp.238-245
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• 2016

A sequence number checking technique is proposed to improve the performance of TCP connections in mobile ad hoc networks. While a TCP connection is initialized, a routing protocol takes the responsibility for checking the hop count between a source and destination pair. If the hop count is greater than a predefined value, the routing protocol decides to use a proxy node. The responsibility of a proxy node is to check the correctness of data packets and inform the missing packets by sending an acknowledgement from a proxy node to the source node. By doing so, the source node is able to retransmit any missing packet in advance without waiting until an end-to-end acknowledgement is received from the destination. Simulation results show that the proposed mechanism is able to increase throughput up to 55% in static network and decrease routing overhead up to 95%in mobile network.

• The KIPS Transactions:PartC
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• v.11C no.3
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• pp.379-386
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• 2004

The WAP 2.0 system is a newly proposed wireless communication system by the WAP Forum for interoperability across Internet environment and the system takes charge of communication between WAP terminals and existing origin Web servers. The purpose of this paper is 1) to construct a WAP 2.0 proxy proposed by the WAP Forum and 2) to improve the WAP Proxy in order to increase communication efficiency between wired and wireless communication objects. The Improved WAP proxy constructed in this study provides links between wired and wireless communication environments using the split-TCP concept. However, unlike the split-TCP connection, The improved WAP proxy maintains TCP's end-to-end semantics and reduces overhead by avoiding operations as much as possible on the upper protocol layer. In addition, The improved WAP proxy supports SACK(Selective Acknowledgement ) option and Timestamp option for speedy re-transmission which leads to reduction of performance degradation. After constructing the improved WAP proxy under Linux environment, experiments have been taken. The experimental results show that, compared with the experiments when a WAP proxy proposed by the WAP Forum is used, both data transmission delay time and data transmission size decrease to show that communication efficiency is increased. In particular, as packet missing ratio Increases, data transmission size decreases, which demonstrates that the improved WAP proxy is very effective for performance improvement in wireless communication environment.

• Proceedings of the Korea Multimedia Society Conference
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• 2000.04a
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• pp.65.1-70
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• 2000

최근 인터넷 사용자의 증가와 인터넷을 이용한 전자상거래가 활발해지면서 TCP/IP 통신 보안에대한 많은 연구들이 진행되고 있다. 이러한 연구들중 SSL(Secure Socket Layer) 은 인증 및 보안 프로토콜로서 인터넷을 이용한 통신 보안에 가장 많이 사용되고있는 방법이다. 본 논문에서는 국내 암호 알고리즘의 표준으로 채택된 SEED 알고리즘을 SSL에 적용하여 서버와 클라이언트의 통신을 128bits 암호화할 수 있는 SSL-Proxy 프로그램을 구현하였으며, Windows 와 Unix 시스템에 모두 적용 가능하도록 모듈화하였다.

• Journal of Satellite, Information and Communications
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• v.8 no.1
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• pp.1-7
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• 2013

Currently satellite communication systems usually use the ACM(Adaptive Coding and Modulation) to extend the link availability and to increase the bandwidth efficiency. However, when ACM system is used for satellite communications, we should carefully consider TCP congestion control to avoid network congestions. Because MODCODs in ACM are changed to make a packet more robust according to satellite wireless link conditions, bandwidth of satellite forward link is also changed. Whereas TCP has a severe problem to control the congestion window for the changed bandwidth, then packet overflow can be experienced at MAC or PHY interface buffers. This is a reason that TCP in transport layer does not recognize a change of bandwidth capability form MAC or PHY layer. To overcome this problem, we propose the adaptive congestion control scheme of TCP for supporting ACM in Satellite PEP (Performance Enhancing Proxy) systems. Simulation results by using ns-2 show that our proposed scheme can be efficiently adapted to the changed bandwidth and TCP congestion window size, and can be useful to improve TCP performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7B
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• pp.431-437
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• 2007

Web proxy caching provides an effective way to reduce access latency and bandwidth requirement. In particular, prefix caching is considered as an alternative for improving video delivery over wide area networks because video objects are usually too large to be cached in their entirety. Nevertheless, many studies have pointed that the user-perceived latency is often not dominated by object transmission time, but rather by setup process such as TCP connection time that precedes it. We propose pre-connecting techniques and show that the techniques can be used efficiently in TCP splicing. Our analysis shows the pre-connection significantly reduces start-up latency and TCP connection time in simple analytical model. The deployment of the proposed pre-connection does not require protocol modification or the cooperation of other entities.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.9
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• pp.700-706
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• 2013

In this paper, we propose a method for applying random linear network coding in satellite communication to improve reliability. In the proposed protocol, network-coded redundancy (NC-R) packets are transmitted in the PEP (Performance Enhancement Proxy). Therefore, if data packets is lost by wireless channel error, they can be recovered by NC-R packets. We also develop the TCP performance model of the proposed protocol and evaluate the performance of the proposed protocol. In the simulation results, It is shown that the proposed protocol can improve the TCP throughput as compared with that of the conventional TCP because the NC-R packets is sent by the sender-side PEP and the receiver-side PEP use these packets to recover the lost packets, resulting in reducing the packet loss in TCP.

• Journal of information and communication convergence engineering
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• v.1 no.4
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• pp.194-198
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• 2003

Recently, the use of TCP/IP protocols over wireless LANs poses significant problems. In this paper, we have analyzed transmission control protocol (TCP) packet transmission time for mobile IP over wireless local area networks (LANs) using a proposed a new random backoff scheme. We call it as a proxy backoff scheme. It is considered the transmission time of TCP packet on the orthogonal frequency division multiplexing (OFDM) in additive white gaussian noise (AWGN) channel. From the results, a proposed proxy backoff scheme produces a better performance than an original random backoff in mobile IP over wireless LANs environment. Also, in OFDM/quadrature phase shift keying (QPSK) medium access control (MAC), we have obtained that the transmission time in wireless channel decreases as the TCP packet size increases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.58-65
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• 2016

Satellite communication is a wide area network (WAN) which provides communication service worldwide. However, the performance of TCP can be seriously degraded in the satellite networks due to limited bandwidth, long round-trip time (RTT) and high bit error rate (BER) over satellite links. In order to improve the performance of TCP, this paper proposes cross-layer Performance Enhancing Proxy (PEP) in digital video broadcasting-return channel via satellite (DVB-RCS) networks. The proposed protocol sets TCP Congestion Window (CWND) size by using satellite resource allocation information exchanged between TCP and the link-layer. we implement PEP testbed based on Linux to evaluate the performance of the proposed protocol. The simulation results show that the proposed protocol performs better than standard TCP both in single and multiple sessions in variant BER, because the proposed protocol sets TCP CWND size by using satellite resource allocation.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.21 no.2
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• pp.119-129
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• 2011

TCP-related Flooding attacks still dominate Distributed Denial of Service Attack. It is a great challenge to accurately detect the TCP flood attack in hish speed network. In this paper, we propose the NIC_Cookie logic implementation, which is a kind of security offload engine against TCP-related DDoS attacks, on network interface card. NIC_Cookie has robustness against DDoS attack itself and it is independent on server OS and external network configuration. It supports not IP-based response method but packet-level response, therefore it can handle attacks of NAT-based user group. We evaluate that the latency time of NIC_Cookie logics is $7{\times}10^{-6}$ seconds and we show 2Gbps wire-speed performance through a benchmark test.

• Journal of Broadcast Engineering
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• v.9 no.2
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• pp.119-130
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• 2004

We have developed a prototype super-high-definition (SHD) digital cinema distribution system that can store, transmit, and display eight-million-pixel motion pictures that have the image quality of a 35-mm film movie. The system contains a movie server, a real-time decoder, and an SHB projector. Using a Gigabit Ethernet link and TCP/IP, the server transmits JPEG2000 compressed motion picture data streams to the decoder at transmission speeds as high as 300 Mbps. The received data streams are decompressed by the decoder, and then projected onto a screen via the projector. By using an enlarged TCP window, multiple TCP streams, and a shaping function to control the data transmission quantity, we achieved real-time streaming of SHD movie data at about 300 Mbps between Chicago and Los Angeles, a distance of more than 3000 km. We also improved the decoder performance to show movies with Image qualities of 450 Mbps or higher. Since UDP is more suitable than TCP for fast long-distance streaming, we have developed an SHD digital cinema UDP relay system, in which UDP is used for transmission over a fast long-distance network. By using four pairs of server-side-proxy and decoder-side-proxy, 450-Mbps movie data streams could be transmitted.