A Performance Enhancing Proxy for terrestrial-satellite hybrid networks

위성 통신은 넓은 지역에 통신 서비스를 제공하는 광역 네트워크이다. 하지만, 위성 통신은 대역폭이 제한되고 매우 긴 전파 지연 시간과 높은 BER(Bit Error Rate)로 인해 위성 통신을 고려하지 않은 TCP의 성능이 저하 된다. 본 논문에서는 위성 통신에서의 TCP 성능을 향상시키기 위해 DVB-RCS(Digital Video Broadcasting-Return Channel via Satellite) 네트워크 환경을 고려한 cross-layer 기반 PEP(Performance Enhancing Proxy) 기술을 제안한다. 제안하는 프로토콜은 TCP와 링크 계층 간 위성 자원 할당 정보를 정보 교환을 통해 최적의 TCP CWND(Congestion Window)를 설정한다. 제안한 프로토콜의 성능 평가를 위해 리눅스 기반의 PEP 테스트 베드를 구현하였다. 성능 평가 결과 다양한 BER에서 제안한 프로토콜은 위성 자원 할당 정보를 이용하여 최적의 TCP CWND 크기를 설정하기 때문에 단일 및 다중 세션 환경에서 기존 TCP 보다 제안한 프로토콜이 더 좋은 성능을 보여준다는 것을 확인할 수 있었다. 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.

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.

As the Internet dramatically changes the world, applications that based on TCP/IP are taking up an increasing proportion in satellite services. Since there are characteristics such as long round trip delay and high bit error rate in satellite communication links, when combined with TCP/IP services, it will lead to frequently data resending and decrease network throughput. An accelerator based on Space Communication Protocol Standard Transport Protocol (SCPS-TP) has been designed and presented in this paper functioning as a Performance Enhancing Proxy (PEP) to improve TCP performance in satellite IP networks. Testing results show that satellite IP networks using the accelerator can achieve higher throughput performance, shorter transfer delay, better stability and stronger flexibility. The accelerator is totally transparent to the applications, and therefore it could be applied to any kind of space communication, and it could also meet the demand for rapid response in military, earthquakes and other emergencies.

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 & Sons, Ltd.

Modified Packet Combining (MPC) scheme is an error correction scheme, which can correct double or, higher bit errors. In some earlier work, a scheme known as Packet Reversed Packet Combining (PRPC) scheme that will correct error if occurs at same bit location of erroneous copies, was studied. Both PRPC and MPC scheme are believed to offer higher throughput and better error correction capability at high bit error rate (BER) and large packet size only. Exact analysis was performed to substantiate this claim of higher throughput and better error correction capability in high as well as in low bit error rate (BER) for large and medium packet size. To combat high bit error rate some researches proposed to use Error Correction Code (ECC) in place of Error Detection Code (EDC) in ARQ scheme. But no conclusive result is found to justify the idea in terms of throughput. The current investigation is an attempt to explore the basic gap. In this paper, we investigate the exact analysis of both PRPC and MPC in a Modified way over Conventional PRPC, and report the findings thereof. We propose a combined protocol of Modified PRPC and MPC, and find that it will offer higher throughput and better error correction capability at high and low BER with medium and large packet size as we have used MPC (Modified Packet Combining) scheme with PRPC (Packet Reverse Packet Combining) scheme in a Modified way by combining BEC (Backward Error Correction) with FEC (Forward Error Correction) Codes for Mobile Communication and Networks.

Currently there is no control for real-time traffic sources in IP networks. This is a serious problem because real-time traffic can not only congest the network but can also cause unfairness and starvation of TCP traffic. A new rate control scheme, RCS, is introduced for real-time traffic in networks with high bandwidth-delay products and high bit error rates. RCS is based on the concept of using dummy packets to probe the availability of network resources. Dummy packets are treated as low priority packets and consequently they do not affect the throughput of actual data traffic. Therefore, RCS requires all the routers in the connection path to support some priority policy. Simulation experiments show that in environments with high bandwidth-delay products and high bit error rates, RCS achieves good throughput performance without penalizing TCP connections.

SUMMARY With the rapid development of wireless network technologies, heterogeneous networks with wired and wireless links are becoming common. However, the performance of TCP data transmission deteriorates significantly when a TCP connection traverses such networks, mainly because of packet losses caused by the high bit error rate of wireless links. Many solutions for this problem have been proposed in the past literature. However, most of them have various drawbacks, such as difficulties in their deployment by the wireless access network provider and end users, violation of TCP’s end-to-end principle by splitting the TCP connection, or inapplicability to IP-level encrypted traffic because the base station needs to access the TCP header. In this paper, we propose a new mechanism without such drawbacks to improve the performance of TCP over wired and wireless heterogeneous networks. Our mechanism employs a receiver-based approach, which does not need modifications to be made to the sender TCP or the base station. It uses the ACK-splitting method for increasing the congestion window size quickly in order to restrain the throughput degradation caused by packet losses due to the high bit error rate of wireless links. We evaluate the performance of our mechanism and show that our mechanism can increase throughput by up to 94% in a UMTS network. The simulation results also show that our mechanism does not significantly deteriorate

The long propagation delay, limited bandwidth and high bit error rate pose great challenges in Media Access Control (MAC) protocol design for underwater acoustic networks. In this paper, we proposed an underwater MAC protocol based on Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA), which is called UW-CSMA/CA (CSMA/CA for underwater). Three areas of improvement are investigated, namely, the control rules, the deferral rules, and the backoff slot time. The simulations in ns2 demonstrate that the throughput performance of UW-CSMA/CA is clearly higher than that of original CSMA/CA protocol. We also conclude some regulations between throughput and network parameters, which provide basis of network optimization.

Communication in the underwater wireless sensor networks (UWSNs) faces many challenges due to the acoustic wave characteristics. Acoustic wave has very limited bandwidth, long propagation delay, high bit error rate (BER), and unreliable communication compared to the radio wave. Therefore, media access control (MAC) protocols proposed in terrestrial wireless sensor networks (TWSNs) cannot be implemented underwater as TWSNs rely on radio waves and enables multiple transmissions at a time without causing a collision. Besides, underwater nodes operate in a half-duplex mode and only allows one transmission at a time. Designing an efficient MAC protocol for underwater time-sensitive applications, such as the oil/gas pipeline and climate change prediction applications is necessary. While each application has its own requirements, the software-based approach promises great enhancements to meet more than one application's requirements. The software-based approach allows us to reconfigure the variables through a software without additional hardware requirements. To address the above issues, this paper proposes a software-based MAC protocol that utilizes optical and acoustic wave for communication and allows multiple transmissions at a time in different directions. This study aims to maximize throughput, packet delivery ratio (PDR), network utilization while minimizing latency.

Long propagation delay, limited bandwidth, and high bit error rate pose great challenges in media access control (MAC) protocol design for underwater acoustic networks. A MAC protocol called slotted floor acquisition multiple access (slotted-FAMA) suitable for underwater acoustic networks is proposed and analyzed. This FAMA based protocol adds a time slot mechanism to avoid DATA packet collisions. However, slotted-FAMA is not suitable for dense networks since the multiple request-to-send (RTS) attempts problem in dense networks is serious and greatly limits the network throughput. To overcome this drawback, this paper proposes a slotted-FAMA based MAC protocol for underwater acoustic networks, called RC-SFAMA. RC-SFAMA introduces an RTS competition mechanism to keep the network from high frequency of backoff caused by the multiple RTS attempts problem. Via the RTS competition mechanism, useful data transmission can be completed successfully when the situation of multiple RTS attempts occurs. Simulation results show that RC-SFAMA increases the network throughput efficiency as compared with slotted-FAMA, and minimizes the energy consumption.

Acoustic waves propagate slowly in water, and time-varying UACs result in inevitably high bit error rate and packet loss rate. The long propagation delay and the error-prone nature of UACs impose challenges on reliable transmissions in UANs. In this article, we identify the challenges for reliable acoustic transmissions and propose a CL-FEC scheme, which achieves opportunistic transmissions to overcome the frequent transmission failures in UACs. CL-FEC adopts fountain codes as a packet-level FEC and adopts channel codes as a bit-level FEC, to realize reliable transmissions over UACs without per-packet feedback. To further improve the throughput of CL-FEC, we formulate the transmissions over UACs into a stochastic throughput optimization problem. A discrete stochastic approximation based algorithm is then developed to achieve the optimal CL-FEC by online exploiting channel estimating and algorithm iterations. Simulation results show the asymptotic convergence and the iterative optimality of the algorithm.

In the definition of advanced 5G scenarios, one of the possible configurations including the satellite link is to consider it to provide a supplementary capacity to enhance backhauling towards data networks. The peculiar satellite physical character- istics and the resulting challenging communication environment (i.e., large propagation delays, possible losses, etc.) are usually tackled with the introduction of Performance Enhancing Proxies (PEPs) agents aimed to improve performance. In this regard, 5G offers the cutting-edge capability to exploit virtualization and slicing concepts, so that PEP can be implemented as a set of Virtualized Network Functions (VNFs) to be dynamically deployed into the network responding to the specific requirement of the target service slice. In this paper we discuss this approach, validated in the frame of an European Space Agency (ESA) project, where a hybrid terrestrial-satellite backhaul is envisaged to enhance performance and system. In particular, we present a QUIC proxy as distributed VNFs aimed to efficiently manage the hybrid link allowing an efficient failover in case of terrestrial link outage or unavailability.

Different from terrestrial sensor networks, underwater sensor networks use acoustic channels for communication and most sensor nodes are mobile due to water current. These distinctions feature underwater sensor networks with highly dynamic topology, high bit error rate, large propagation delay, and low available bandwidth. Traditional ARQ series are not suitable due to their frequent feedbacks, which is undesirable in underwater environment. On the other hand, pure FEC can't apply into underwater sensor networks, not only because of its complexity, but also because it needs some feedbacks. This paper studied transport protocol in underwater sensor networks, implemented a reliable lightweight RFEC-based encoding and decoding algorithm. Then combine the algorithm with ARQ to a transport protocol. In this way, take advantages of FEC to deal with high bit error, and ARQ to avoid feedbacks. Through simulation experiment on method of random sequences generation, parameters selection, and transmission strategy, some useful conclusion is gotten. It provides practical data and references on practical application of underwater sensor networks.

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.

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.