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

• Proceedings of the Korean Information Science Society Conference
• /
• 2007.06d
• /
• pp.252-256
• /
• 2007

Mobile IP는 단말에게 Mobility를 제공해 줌으로써 이동하면서도 인터넷에 접속할 수 있게 해준다. 하지만 핸드오프시 지연과 데이터 로스의 문제점이 있어 이를 해결하기 위해 Fast Handover 기술이 개발되었다. 또한 앞으로의 이동성 관리는 단말 기반이 아닌 네트워크 기반으로 이루어지면서 Proxy-Mobile IP가 등장 하였고 Proxy-Mobile IP에서도 빠른 이동성 관리를 위해 Fast Handover 기술이 적용될 것이다. 하지만 Fast Handover에서도 터널 확장 문제로 인한 라우팅 경로의 비효율성이 나타나게 된다. 본 논문에서는 IETF MONAMI6의 MCoA 기술을 이용하여 Fast Handover Proxy Mobile IP의 핸드오프 성능 개선 방안을 제안한다.

• Journal of Advanced Navigation Technology
• /
• v.6 no.4
• /
• pp.290-295
• /
• 2002

In Mpeg-4 system, objects are composed of ES(Elementary Stream). Each of the objects is managed independently by object-based coding and is transmitted via DMIF(Delivery Multimedia Integration Framework). The data streams in Mpeg-4 are transmitted with using DVB-Data Carousel which can improve the reliability and efficiency by cyclic retransmission. This paper describes a system which transmits some part of data stream of Mpeg-4 object with using DVB-Data Carousel to clients via satellite. This also uses a performance enhancing proxy server for reducing round trip time between ground network and satellite.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.1
• /
• pp.58-65
• /
• 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 Communications and Networks
• /
• v.13 no.5
• /
• pp.518-524
• /
• 2011

A high assurance IP encryption (HAIPE) compliant protocol accelerator is proposed for military networks consisting of red (or classified) networks and black (or unclassified) networks. The boundary between red and black sides is assumed to be protected via a HAIPE device. However, the IP layer encryption introduces challenges for bandwidth on demand satellite communication. The problems experienced by transmission control protocol (TCP) over satellites are well understood: While standard modems (on the black side) employ TCP performance enhancing proxy (PEP) which has been shown to work well, the HAIPE encryption of TCP headers renders the onboard modem's PEP ineffective. This is attributed to the fact that under the bandwidth-on-demand environment, PEP must use traditional TCP mechanisms such as slow start to probe for the available bandwidth of the link (which eliminates the usefulness of the PEP). Most implementations recommend disabling the PEP when a HAIPE device is used. In this paper, we propose a novel solution, namely broadband HAIPE-embeddable satellite communications terminal (BHeST), which utilizes dynamic network performance enhancement algorithms for high latency bandwidth-on-demand satellite links protected by HAIPE. By moving the PEP into the red network and exploiting the explicit congestion notification bypass mechanism allowed by the latest HAIPE standard, we have been able to regain PEP's desired network enhancement that was lost due to HAIPE encryption (even though the idea of deploying PEP at the modem side is not new). Our BHeST solution employs direct video broadcast-return channel service (DVB-RCS), an open standard as a means of providing bandwidth-on-demand satellite links. Another issue we address is the estimation of current satellite bandwidth allocated to a remote terminal which is not available in DVBRCS. Simulation results show that the improvement of our solution over FIX PEP is significant and could reach up to 100%. The improvement over the original TCP is even more (up to 500% for certain configurations).

• Information and Communications Magazine
• /
• v.32 no.10
• /
• pp.11-17
• /
• 2015

네트워크 중심전에서 위성통신체계에 대한 중요성은 증가하고 있고, 차기 위성 통신 체계의 요구사항들을 만족하기 위해서는 PEP (Performance Enhancing Proxy) 기술의 적용이 필수적이다. 본 고에서는 차기 군 위성 통신 체계에서 적용 가능한 PEP 주요기술들과 상용 제품들의 특성을 알아보고, cross-layer 기반 PEP기술과 SOTM (Satellite communication On-The-Move) 단말을 위한 PEP 기술 동향에 대해서 살펴본다.

• Journal of KIISE:Computing Practices and Letters
• /
• v.8 no.4
• /
• pp.450-456
• /
• 2002

Open source web service softwares are usually running on UNIX-based operating systems. Choosing an operating system can affect web system performance. In this paper, we describe a source - code-level time measurement tool and measure a service time of each system call that Squid - open source web proxy cache - makes. We run Squid 2.4.STABLEl on Linux 2.4.2 and Solaris 8, and we compare the measured time. As a result, Linux 2.4.2 performs better than Solaris 8. It can be used as a guide for selecting system software on building web service using open source software, and also be used as a basis for enhancing the operating system performance of supporting web service software.

• IEMEK Journal of Embedded Systems and Applications
• /
• v.1 no.2
• /
• pp.64-72
• /
• 2006

The long propagation delay over satellite internet causes degradation of TCP performance in slow start phase. Especially, web traffic performance is greatly reduced by low throughput in slow start phase. To improve web traffic performance, we propose the Dynamic ACK Generation Scheme which generates ACKs and considers sender RTO in PEP (Performance Enhancing Proxy). The Normal ACK generation mechanism improves TCP throughput, and also decreases sender RTO. if PEP stops generating ACKs, TCP performance will be reduced by frequent RTO expiration. To solve this problem, our scheme adjusts RTO using ACK generation interval. And it supports retransmission mechanism for loss recovery in PEP. The results of the performance analysis provide a good evidence to demonstrate the efficiency of our mechanisms over satellite internet.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.13 no.5
• /
• pp.121-133
• /
• 2013

Defect-free transfer service on the Next-generation wireless network extensive roaming mobile node (MN) to provide efficient mobility management has become very important. MIPv6(Mobility IPv6) is one of mobility management scheme proposed by IETF(Internet Engineering Task Force), and IPv6-based mobility management techniques have been developed in various forms. One of each management techniques, IPv6-based mobility management techniques for PMIPv6 (MIPv6) system to improve the performance of a variety of F-PMIPv6 (Fast Handover for Proxy MIPv6) is proposed. However, the F-PMIPv6 is cannot be excellent than PMIPv6 in all scenarios. Therefor, to select a proper mobility management scheme between PMIPv6 and F-PMIPv6 becomes an interesting issue, for its potenrials in enhancing the capacity and scalability of the system. In this paper, we develop an analytical model to analyze the applicability of PMIPv6 and F-PMIPv6. Based on this model, we design an Secure Smart Mobility Support(SSM) scheme that selects the better alternative between PMIPv6 and F-PMIPv6 for a user according to its changing mobility and service characteristics. When F-PMIPv6 is adopted, SSM chooses the best mobility anchor point and regional size to optimize the system performance. Numerical results illustrate the impact of some key parameters on the applicability of PMIPv6 and F-PMIPv6. Finally, SSM has proven even better result than PMIPv6 and F-PMIPv6.

• Asian Journal of Innovation and Policy
• /
• v.7 no.3
• /
• pp.461-488
• /
• 2018

This paper explores the relationship between network cooperation, innovation, internationalization and economic performance of manufacturing small and medium enterprises (SMEs) of engineering goods industry located in Bangalore city, India. At the outset, it is observed that SMEs receive the maximum assistance in the realm of product specifications. Moreover, they do not resort to manufacturing new products as much as they resort to product modifications or process improvements. Further, it is found (using Chi-square test of independence) that higher the network assistance received from an external network, greater is the innovation performance of SMEs. Subsequently, using analysis of variance (ANOVA), export intensity (proxy for internationalization performance) of SMEs is found to have a significant positive association with both the degree of their network cooperation and of their innovation performance. Lastly, it is observed that higher the degree of each of network cooperation, innovation performance and internationalization performance, better is the economic performance (measured by total sales turnover) of SMEs. These results have significant implications for the policy makers of the country to give due attention to network cooperation, innovation and internationalization as the means of enhancing the economic performance of SMEs.