위성 통신에서 Cross-layer 기반 PEP 성능 평가

In this paper, we propose a TCP congestion window (CWND) tuning scheme which considers the resource allocation information of satellite link and the number of sessions. The proposed scheme sets TCP congestion window size by using satellite resource allocation information exchanged between TCP and the link layer and the number of session. To evaluate the performance, we implemented the proposed scheme on TCP Linux kernel over TCP-splitting based performance enhancing proxy (PEP) test-bed. The results show that the performance of proposed protocol better than existing TCP protocols, both in single and multiple sessions in variant bit error rates (BER) notably in higher BER.

Mobile computing and security in Internet have become two of the most important challenges in the information technology world. Among wireless technologies which support user mobility, satellites will play a very important role. Unfortunately, TCP does not perform well on satellite channels because of the related high delay-bandwidth product, high bit error rate (BER) and burst errors mainly due to shadowing. In order to obtain improvements in TCP performance, an approach local to the satellite link could be adopted. In fact, recently, some studies showed the effectiveness of the use of a reliable data link protocol that is well suited to mobile geo-stationary satellite channel characteristics. However, the resultant more variable end-to-end delay causes, as a side effect, a new problem: the competition between retransmission mechanisms at transport layer and data link layer. The introduction of a suitable performance enhancing proxy (PEP) on the satellite gateway has proved to be a viable technique to face the problem. However, the compatibility with the usage of network layer security mechanisms, such as IPSec, should be pursued. This paper just deals with the definition of an IPSec-aware TCP PEP, called secure PEP (SPEP), that is completely transparent to IPSec architecture. The performances of SPEP have been validated in the context of Web application by using network simulator tool. The simulation results, in terms of Web-page download mean time, have shown that the proposed solution provides substantial improvements in TCP performance.

차세대 무선통신에서는 현재 서비스 되고 있는 성능보다 높은 BER(Bit Error Rate)의 성능을 요구한다. 기존의 DVB-RCS(Digital Video Broadcasting - Return Channel via Satellite)에서 사용중인 이진 터보 코드(Double binary Turbo code)는 높은 SNR(에서 오류마루 현상이 발생하여 차세대 무선통신에서 사용하기가 어려움이 있다. 따라서 본 논문에서는 DVB-RCS NG에 적합한 부호화 방식으로 3D-터보 코드(Tthird-dimension Turbo code)의 부복호화기의 구조를 분석하고 성능분석 하였다. 3D-터보 코드는 기존의 DVB-RCS 방식에 rate-1인 post-encoder를 첨가시켜 오류마루 현상을 보완한 부호화기이다. 3D-터보 코드는 post-encoder의 형태, 인터리빙 기법, <TEX>${\lambda}$</TEX>값의 변화에 따라 성능이 달라지므로 본 논문에서는 각 파라메타에 대한 최적의 값을 제시하였다. 전체적으로 3D-터보 코드가 기존의 DVB-RCS 터보 코드에 비해 성능이 우수하고 기존의 문제점인 오류마루 현상을 해결할 수 있음을 알 수 있다. The next generation wireless communication systems are required high BER performance better than present performance. Double binary Turbo code have error floor at high SNR, so it cannot be used in next generation wireless communication system. Therefore, many methods are proposed for overcome error floor at DVB-RCS NG(next generation). In this paper, we analysis structure of third-dimension Turbo code(3D-turbo code). 3D-Turbo code overcomes error flow by additive post-encoder in conventional DVB-RCS Turbo code. Performance of 3D-Turbo code is changed by post-encoder form, interleaving method, value of <TEX>${\lambda}$</TEX>. So we are simulated by those parameter and proposed optimal form. By a result, performance of 3D-Turbo is better than conventional DVB-RCS Turbo code and it overcome error floor of conventional DVB-RCS Turbo code.

This paper presents a TCP/IP-based architecture (IPSecOPEP) to resolve the interoperability issue between PEPs (Performance Enhancing Proxies) and IPSec (Internet Protocol Security). Where this problem is due to the cryptographic protection of TCP header by IPSec ESP protocol, which prohibits TCP enhancing mechanisms to be performed by PEPs. The key idea of this solution is that IPSec devices can perform well as a bridge between end users and PEPs in such situations, because they can access to both TCP headers of original packets and IPSec headers of encrypted packets. By this way, IPSec devices can perform a simple mapping between original TCP headers and their corresponding IPSec headers to resolve the interoperability issue. In our proposed IPSecOPEP architecture, we add a new components to the standard TCP/IP stack for IPSec devices and PEPs proxies, to ensure cooperatively and transparently the interoperability between them, without affecting the security privacy and performance level in such situations. In fact, this solution doesn't need to exchange any secret information about IPSec-related security associations. Furthermore it doesn't imply the use of any additional headers to IPSec packets by the PEPs. However, IPSec devices should coordinate between end users and PEPs to ensure spoofing mechanism, to avoid slow start problem of a standard TCP. After that, PEPs can continue to apply other enhancing mechanisms over the satellite link. Hence, this solution presents a double advantages concerning both the security and the performance at once. Moreover, the components of this solution can be easily standardized, implemented, integrated and enabled, in IPSec and PEPs devices.

Satellites have played an important role in global telecommunications. However, transmission control protocol (TCP) suffers performance degradations over satellite links due to the long propagation delay and high bit‐error rate. Among methods proposed to alleviate the impact of satellite link characteristics on TCP performance, split TCP connections separated by performance enhancement proxies (PEPs) have been proven attractive because they can keep TCP configurations in the end systems unchanged. While many protocols applied over satellite links between PEPs can effectively mitigate the effect of high loss rates, the long latency still limits the effectiveness of congestion control in these protocols. To minimize the effect of congestion we propose to take advantage of active queue management at the medium access control layer to provide immediate cross‐layer feedback to the TCP segment over satellite. This approach also achieves proper differentiation between packet losses due to channel errors and congestion. Simulation results show that our novel mechanism can give substantial improvements in TCP performance over satellite networks, compared to the best performing version of TCP with or without PEPs. Copyright © 2006 John Wiley &amp; Sons, Ltd.

SUMMARYApplications that use the reliable Transmission Control Protocol (TCP) have a significant degradation over satellite links. This degradation is mainly a consequence of the congestion control algorithm used by standard TCP, which is not suitable for overcoming the impairments of satellite networks. To alleviate this problem, two TCP Performance Enhancing Proxies (PEPs) can be deployed at the edges of the satellite segment. Then these PEPs can use different mechanisms such as snooping, spoofing and splitting to achieve a better TCP performance. In general, these mechanisms require the manipulation of the Internet Protocol (IP) and TCP headers that generates a problem when deploying the standard IP security (IPsec) protocol. The security services that IPsec offers (encryption and/or authentication) are based on the cryptographic protection of IP datagrams, including the corresponding IP and TCP headers. As a consequence, these cryptographic protections of IPsec conflict with the mechanisms that PEPs use to enhance the TCP performance in the satellite link. In this article, we detail the reasons that cause this conflict, and we propose three different approaches to deploy IPsec in a scenario with TCP PEPs. Our proposals provide different trade‐offs between security and TCP performance in some typical scenarios that use satellite networks. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Almost a decade long research on the performance of TCP in wireless networks has resulted in many proposals and solutions to the problem of TCP throughput degradation. Several of these measures, however, have their share of drawbacks. With the continuing emergence of wireless technologies ever since the work on TCP performance over wireless began, smart link-layer mechanisms like adaptive modulation and coding, power control, and incremental redundancy have been designed and deployed. In this work, we outline a cross-layer optimization framework based on the congestion control dynamics of a bulk-transfer TCP flow and demonstrate its application to networks which offer link-layer adaptive measures. We begin by observing that the TCP's congestion window dynamics are comprised of certain recurring patterns which we term as cycles. We then overlay a TCP throughput optimization methodology that selects link-layer transmission modes (e.g. modulation scheme, coding rate, transmission power, or a combination thereof) in accordance with TCP dynamics and wireless channel conditions. We provide insights into the working of the optimization procedure which protects TCP segments against losses on the wireless channel when the TCP congestion window size (in bytes) is below the bandwidth-delay product of the network. The protection against wireless channel losses is rendered by the link-layer by employing robust modulation and coding schemes, high transmission power, etc. We show that TCP dynamics aware link adaptation measures lead to substantial enhancement of TCP throughput in EGPRS and IEEE 802.11a networks

It has long been understood that Transport Control Protocol (TCP) traffic performs poorly across satellite links. To overcome this performance challenge, SATCOM users have traditionally used Performance Enhancing Proxies (PEP) to "accelerate" TCP traffic. PEPs work by breaking the end-to-end TCP connection, running a different layer 4 protocol across the satellite link, and proxying the TCP connections with each end host. To do this, PEPs must be able to inspect and modify the entire IP packet, including the TCP segment header, to ensure proper handling of TCP traffic over the link. The Department of Defense (DoD) is in the process of implementing the Global Information Grid (GIG), an Internet-like network for warfighters anywhere on Earth. Current plans call for the GIG to transition to a "Black", or IP-encrypted, Core in the future [3]. Within the Black Core, IP packets will be completely encrypted, obscuring all information at layer 3 and above. Such an approach would render existing PEPs useless if placed in the Black Core. This is referred to in this paper as the Black Core problem. Many solutions have been proposed to the Black Core problem. Proposed solutions have included making changes to the network architecture, to the network protocols, or both. This paper expands upon the overview of PEP-based solutions presented in [4], and details several additional approaches. Additionally, this paper overviews the advantages and disadvantages for each method.

Adaptation of TCP for satellite links has been the subject of many research studies in the last decade. In many such studies, Performance Enhancing Proxies (PEPs) and modified TCP congestion control algorithms have been reported to considerably improve TCP performance over satellite systems. In parallel to Transport layer developments, Link layer mechanisms as well as satellite hardware design are also evolving, providing more reliable transmission and higher capacity utilisation. Under the new light of these evolutions, this paper presents a simulation campaign, comparing the performance of different TCP variants over a satellite network using PEPs. The second contribution of this paper is the performance assessment of a novel TCP congestion control mechanism based on cross-layer design. Cross-layer adaptation is a relatively new idea in network design, based on the vertical integration of protocol layers. Simulation results for this mechanism demonstrate the strong relationship between the Transport and Link layers and illustrate the benefits of joint analysis and design. © 2007 by University of Surrey.

The DVB-RCS standard provides a framework for Multi-Frequency TDMA (MF-TDMA) and dynamic resource (frequencies and time slots) allocation over satellite links. Nevertheless, MF-TDMA and dynamic resource allocation alone are not sufficient to achieve satisfactory throughput for TCP, the dominant transport protocol in IP-based networks such as the Global Information Grid (GIG) system, due to the inherent large delay-bandwidth product of the satellite links. Various mechanisms called TCP Performance Enhancement Proxies (PEP) are proposed to improve the performance of TCP over large delay-bandwidth product networks. However, typical TCP PEPs do not support GIGpsilas layer-3 security standard HAIPE (High Assurance Internet Protocol Encryption). In this paper, we identify eXplicit Control Protocol (XCP) as a desired performance enhancement mechanism, and propose a novel system architecture that integrates DVB-RCS, XCP and HAIPE. We implement XCP in the network simulator QualNet and evaluate its performance against that of TCP. Our simulation results show that XCP achieves higher throughput and fairer bandwidth allocation among competing traffic flows in DVB-RCS systems than TCP.

Router Assisted congestion control Protocols (RAPs) appear to be the most efficient solutions to the TCP performance degradation issue in high Bandwidth Delay Product (BDP) networks. Global deployment of RAPs such as XCP, VCP, and MPCP however, has been challenging due to their need for router support. In this paper, we propose RAPPEP a framework for deploying RAPs on potential congestion zones such as satellite links that are locally utilizing the architecture of TCP Performance Enhancement Proxy (PEP). Such a marriage allows for an immediate deployment of RAPs without the need for global router support, while still being able to take advantage of sophisticated RAPs. Beyond the deployed congestion zone, RAPPEP is completely transparent to the rest of the network including end nodes and other routers. Adapting from two implementations of RAPs and an implementation of TCP PEP (PEPSal), we implement and integrate RAPPEP in the Linux kernel and demonstrate its performance improvement compared to PEPSal through emulation studies.

In terrestrial-satellite hybrid networks, traditional TCP performance degrades a lot due to long propagation delays and high bit error rates link. Performance enhancing proxy(PEP) can shorten round trip time loop time and Peach can enhance the performance over high bit error rates link. In this paper, we propose a new scheme that combines PEP and TCP Peach for terrestrial-satellite hybrid networks. The scheme could reduce the negative impact on performance (in terms of throughput). To obtain an analysis result, we also introduce a mathematic model for our PEP. The analysis and simulation results demonstrate that our scheme could significantly improve the network performance than traditional TCP protocols.

Integration of different networks enhances sustainable applications but specific vulnerabilities must be faced up too. New network components often are introduced to efficiently adapt different technologies, whereas in some cases they can be exploited as sources for generation of anomalous events in the interconnected networks attributable to security attacks. This paper deals with security for heterogeneous and inter-operable communication networks including a satellite segment, focusing on the application of an Intrusion Detection System (IDS) on the target scenario. The baseline envisages the presence of Performance Enhancing Proxies (PEPs) at the edges of satellite links, which implies the twofold effect of improving TCP performance but also increasing a PEP-related vulnerability due to the violation of the end-to-end semantic of TCP. The paper addresses the above mentioned issue through the realization of a test bed including a real geostationary satellite link operated by Telespazio. Outcomes of experiments show the effectiveness of the application of the proposed IDS system.

This paper introduces an advanced E-education provision via space systems for Africa or any other regions in remote dispersed communities, such as rural, mining, agriculture, surveying, construction, tourism, military and etc. Based on the specific needs and requirements E-education implies significant broadband applications, interconnectivity, and timely and quality-assured content delivery of service. The E-education solutions of distance learning and training for remote and rural areas, which are beyond range of terrestrial and short distance wireless cellular facilities, cannot provide broadband access without space-enabled communication solutions, such as satellite constellations and Stratospheric Platform Systems (SPS) or High Altitude Platforms (HAP). This paper also discusses the integration challenges that are presented by combining space solutions for implementation E-education and learning in rural and mobile environments. Configuration of in-house development of all segments, installation of the scale-down Digital Video Broadcasting-Return Channel via Satellite (DVB-RCS) Hub (Gateway), Ground Network and Very Small Aperture Terminal (VSAT), known as Fixed Interactive Terminals (FIT), for E-education, distance learning and staff training initiative in Africa are described.

An ad hoc network is a dynamically forming temporary network with a collection of wireless mobile nodes. It does not use any centralized administration or existing network infrastructure. In wireless networks, improving TCP performance largely depends on congestion window size. Both contention and congestion affect the TCP performance. A contention problem occurs in network when adjacent nodes shared channel to transmit packets. Channel contentions cause network congestion because of a lack of coordination between the transport layer and the medium access layer. Due to the channel interference the Bandwidth Delay Product cannot reach to maximum value as in wired network. Packet loss occurs at MAC layer due to congestion. In ad hoc networks, both contention and congestion can severely affect the performance of TCP. In our work, we show that the over-injection of conventional TCP window mechanism results in severe contentions, and medium contentions cause network congestion. The idea is to dynamically adjust the congestion window to improve TCP performance by reducing the congestion window overshooting problem. We study the network performance such as throughput, Packet delivery ratio, and end-to- end delay when congestion control mechanism is used.