Performance of DTN protocols in space communications

Delay/disruption tolerant networking (DTN) was developed to enable automated network communications despite the long link delay and frequent link disruptions that generally characterize space communications. The performance of DTN convergence layer adapter (CLA) protocols over asymmetric space communication channels has not yet been comprehensively characterized. In this paper, we present an experimental performance evaluation of DTN CLA protocols for reliable data transport over a space communication infrastructure involving asymmetric channel rates, with particular attention to the recently developed Licklider transmission protocol (LTP) CLA (i.e., LTPCL). The performance of LTPCL is evaluated in comparison with other two reliable CLAs, TCP CLA and a hybrid of TCP CLA and LTPCL, for long-delay cislunar communications in the presence of highly asymmetric channel rates. LTPCL is also evaluated and analyzed in a deep-space communication scenario characterized by a very long link delay and lengthy link disruptions.     

深空、自由空间、非可视散射和水下激光光子通信

激光光子通信是国际通信前沿研究领域的一个重要的研究方向。近年来激光光子通信技术被广泛地应用于深空通信,卫星与卫星激光通信,自由空间通信,非可视散射通信和水下通信等领域内。首先,由于自由空间激光光子通信系统的高下传速率优势,使其成为未来深空通信重要的研究方向。其次,基于自由空间和非可视散射光子通信方式的分布式传感网络逐渐从实研室走向实际应用。在农业土壤质量检测、地震灾害事件、结构件压力、医疗参数数据、污染物输运和军事应用领域具有广泛的应用价值。另外,水下光子通信技术能够满足与水下观测和海底检测以及钻井平台相关的研究和检测所需要的高速率通信需求。总之,由于激光和光子探测技术的独特优势,光子通信技术研究兴趣日益强劲,将在深空、自由空间和水下通信中被广泛的应用和深入研究。     

Performance evaluation of a TCP proxy in WCDMA networks

The article addresses the end-to-end performance of TCP in a scenario where WCDMA is used as the access link. In particular, the performance gain that can be achieved by placing a TCP split connection proxy in the WCDMA core network is examined. It is well known that performance enhancing proxies are able to improve the performance of TCP over wireless links that suffer from impairments. However, while previous work on TCP proxies for wireless systems either focused on other wireless systems, like wireless LAN or satellites, or provided a more generic framework, we address in detail the characteristics of a WCDMA access scenario supported by a TCP proxy. The characteristics of WCDMA as perceived by TCP are discussed thoroughly. We argue that the motivation for introducing a proxy is only to overcome problems stemming from a large bandwidth delay product and not to assist local transport layer error recovery at the wireless link. Based on simulations that consider both link layer protocols and TCP, the end-to-end performance for file downloads is investigated. Simulation results show that a proxy can significantly improve performance in the case of high data rates like 384 kb/s. For lower data rates, like 64 and 128 kb/s, it is sufficient to use a well configured TCP implementation.     

Controlling window protocols for time-constrained communication inmultiple access networks

The authors examine the use of a group random-access protocol based on time windows for supporting time-constrained communication applications in a multiple-access network. First they formulate a policy for controlling protocol operation to minimize the percentage of messages with waiting times greater than some given bound. A semi-Markov decision model is then developed for protocol operation, and three of the four optimal control elements of this policy are determined. Although the semiMarkov decision model can also be used to obtain performance results, the procedure is to computationally expensive to be of practical use. Thus, an alternate performance model based on a queuing system with impatient customers is developed. Protocol performance under the optimal elements of the control policy shows significant improvements over cases in which the protocol is not controlled in this manner. Simulation results are presented to corroborate the analytic results     

Performance of TCP extensions on noisy high BDP networks

Experiments on high bandwidth delay product (BDP) networks assist in the design and understanding of future global networks. This paper describes the results of experiments with different implementations of TCP on a high speed ATM/SONET network over high delay and noisy channels. Comparisons are also made with host/traffic configurations over various smaller BDP systems, experimental comparisons of three different implementations of TCP; TCP Reno, TCP new Reno, and TCP SACK as a function of bit error rates (BER) and round-trip times (RTT) are presented     

Performance evaluation of HTTP/TCP on asymmetric networks

As the number of Internet users grows, new network technologies are emerging. Those include ADSL and cable modem, which essentially provide asymmetric bandwidth for uplink and downlink to the user's connection. In this paper, we investigate the behaviour of HTTP/TCP protocols on such asymmetric networks, and present the analytic results of the mean throughput of TCP. The transfer time of Web documents by HTTP over TCP is also derived. In the analysis, we consider newer HTTP/TCP protocols, HTTP/1.1 and TCP Vegas, in addition to HTTP/1.0 and TCP Tahoe. We then investigate the appropriate combination of HTTP and TCP protocols on the asymmetric network. The results show that the effect of HTTP/1.1 is quite small, but TCP Vegas can improve the performance in asymmetric networks if it is appropriately modified as in our proposal. Copyright © 1999 John Wiley & Sons, Ltd.     

Performance evaluation of transport protocols in cloud data center networks

Photonic Network Communications - In recent years, cloud data centers have received increased attention by the research community, due to their key function of hosting a big number of cloud...     

Space link simulator for development of new packet-based space communication protocols

Terrestrial network-based file transfer protocol is known to be unacceptable for the space network environment. The Consultative Committee for Space Data Systems (CCSDS) is about to propose a new file transfer protocol for use in both space and ground-based networks, named CCSDS File Delivery Protocol (CFDP). CFDP is based on packet oriented protocols as its underlaying network layer. The supported packet protocols include CCSDS packet standard protocol and TCP/IP. The space communication link displays specific characteristics different from those of terrestrial ones: larger link delay, higher bit error rates, bursts of errors, packet deordering, etc. For use in CFDP implementation, a packet protocol-based space link simulator is designed and implemented. This space link simulator, named LinkSim, can simulate not only distance driven link delay, but also link quality and link diversity. This paper presents the organization of the space link simulator and the algorithms used to emulate each link characteristic feature. The test shows that the LinkSim program simulates exactly the expected space link environment. An example configuration is also discussed at the end of this paper. Copyright © 1999 John Wiley & Sons, Ltd.     

Performance analysis of multiple access protocols for multimediasatellite networks

In this paper, several TDMA-based packet multiple access protocols are studied and evaluated in the geostationary satellite environment. The distributed queueing random access protocol, DQRAP, originally proposed for HFC networks is adapted to the satellite environment. Another protocol, the announced retransmission random access protocol, ARRA, proposed for wireless networks is also studied. Both protocols are modeled and simulated in a VSAT network context. We then propose a new protocol which combines the advantages of both studied schemes and is more adapted to interactive multimedia applications over satellite uplinks. The generalized retransmission announcement protocol, GRAP, regroups the immediate access by contention at low loads, and the reservation access. At higher loads, to achieve a better channel efficiency. An analytical model is proposed to calculate the channel throughput obtained by GRAP under different loading conditions. Simulation results illustrate an improved throughput/delay characteristics and a higher protocol stability compared to both DQRAP and ARRA. Enhanced versions of the protocol are also proposed and evaluated to further improve its efficiency, with reasonable additional complexity     

深空通信网络协议的发展与展望

分析了发展深空通信网络的需求,结合深空通信网络的特点,对深空通信网络协议体系和路由策略等的技术现状进行了综述,对其中的关键技术进行了分析,并对深空通信网络的未来发展进行了展望。     

Performance management of multiple access communication networks

This paper focuses on conceptual design, development, and implementation of a performance management tool for computer communication networks to serve large-scale integrated systems. The objective is to improve the network performance in handling various types of messages by on-line adjustment of protocol parameters. The techniques of perturbation analysis of Discrete Event Dynamic Systems (DEDS), stochastic approximation (SA), and learning automata have been used in formulating the algorithm of performance management. The efficacy of the performance management tool has been demonstrated on a network testbed. The conceptual design presented offers a step forward to bridging the gap between management standards and users' demands for efficient network operations since most standards such as ISO (International Standards Organization) and IEEE address only the architecture, services, and interfaces for network management. The proposed concept for performance management can also be used as a general framework to assist design, operation, and management of various DEDS such as computer integrated manufacturing and battlefield C³ (Command, Control, and Communications)     

Multiple-access protocols for satellite packet communication networks: A performance comparison

This paper considers satellite packet communication networks with a large population of bursty users and presents an analytic comparison of the throughput versus average message delay trade-off characteristics of multiple-access protocols. The following six multiple-access protocols are examined: 1) slotted ALOHA, 2) reservation-ALOHA, 3) a reservation protocol with a slotted ALOHA reservation channel, 4) a reservation protocol with a TDMA reservation channel, 5) SRUC (Split Reservation Upon Collision), and 6) fixed assigned TDMA. All the protocols are required to ensure that all packets of a message are correctly received in the proper order at the destination. Then, a unified presentation of the delay-throughput performance of the protocols is given by means of an analytical technique called equilibrium point analysis. The throughput versus average message delay tradeoff characteristics are compared taking into account the system stability.     

Performance improvement of TCP in ad hoc networks by mitigating channel contention

In ad hoc networks, the spatial reuse property limits the number of packets which can be spatially transmitted over a path. In standard Transmission Control Protocol (TCP), however, a TCP sender keeps transmitting packets without taking into account this property. This causes heavy contention for the wireless channel, resulting in the performance degradation of TCP flows. Hence, two techniques have been proposed independently in order to reduce the contention. First, a TCP sender utilizes a congestion window limit (CWL), by considering the spatial reuse property. This prevents the TCP sender from transmitting more than CWL number of packets at one time. Second, a delayed ack (DA) strategy is exploited in order to mitigate the contention between the TCP ACK and DATA packets. Recently, although TCP‐DAA (Dynamic Adaptive Acknowledgment) attempts to utilize a CWL‐based DA strategy, TCP‐DAA overlooks a dynamic correlation between these two techniques. This paper, therefore, reveals the dynamic correlation and also proposes a protocol which not only reduces the frequency of the TCP ACK transmissions but also determines a CWL value dynamically, according to network conditions. Simulation studies show that our protocol performs the best in various scenarios, as compared to TCP‐DAA and standard TCP (such as TCP‐NewReno). Copyright © 2009 John Wiley & Sons, Ltd.     

Performance analysis of high-speed TCP protocols in LTE X2 handover under realistic operational conditions

Telecommunication Systems - Broadband mobile networks have rapidly evolved over the last years. The unique environment they operate, however, sets new challenges for the Transmission Control...     

一种应用于深空通信的微弱信号捕获算法

针对低信噪比、高动态条件下深空测控通信信号捕获概率低以及复杂度较高的问题,首先分析了深空测控通信信号捕获的难点以及信号循环平稳特性,然后在此基础上提出了一种基于循环相关的新算法。计算机仿真结果证明新算法捕获门限达24 dBHz,适应频率动态达800 Hz/s;新算法较传统的捕获算法,在相同门限条件下的频率动态适应范围提升了约两个数量级。该方法已被应用于我国第一个深空测控站的建设,工作性能稳定可靠,有效地解决了低信噪比下深空站抑制载波信号的捕获问题。     

A novel approach of limited-randomness fountain codes in deep space communication

Digital fountain is applied into deep space communication for its rateless and non-feedback forward error correction. However, the long code length and encoding overhead are confined factors to guarantee a considerable recovery probability as power and buffer-limited equipment in deep space environment. At the same time, the typical fountain decoding is sub-optimum decoding algorithm. We propose a new approach, Dependent Sequences Compensation Algorithm (DSCA), to improve the encoding efficiency by restricting the randomness in fountain encoding. While decoding algorithm is also optimized by redundant information in stopping set. The results show that the optimized method can obtain a 10⁻⁴ decoding failure rate with overhead under 0.20 for code length 500, which indicates the usefulness of the proposed approach in deep space communication.     

Exploring the design space of reliable multicast protocols for wireless mesh networks

Many important applications in wireless mesh networks require reliable multicast communication, i.e., with 100% packet delivery ratio (PDR). Previously, numerous multicast protocols based on automatic repeat request (ARQ) have been proposed to improve the packet delivery ratio. However, these ARQ-based protocols can lead to excessive control overhead and drastically reduced throughput. In this paper, we present a comprehensive exploration of the design space for developing high-throughput, reliable multicast protocols that achieve 100% PDR.Motivated by the fact that 802.11 MAC layer broadcast, which is used by most wireless multicast protocols, offers no reliability, we first examine if better hop-by-hop reliability provided by unicasting the packets at the MAC layer can help to achieve end-to-end multicast reliability. We then turn to end-to-end solutions at the transport layer. Previously, forward error correction (FEC) techniques have been proved effective for providing reliable multicast in the Internet, by avoiding the control packet implosion and scalability problems of ARQ-based protocols. In this paper, we examine if FEC techniques can be equally effective to support reliable multicast in wireless mesh networks. We integrate four representative reliable schemes (one ARQ, one FEC, and two hybrid) originally developed for the Internet with a representative multicast protocol ODMRP and evaluate their performance.Our experimental results via extensive simulations offer an in-depth understanding of the various choices in the design space. First, compared to broadcast-based unreliable ODMRP, using unicast for per-hop transmission only offers a very small improvement in reliability under low load, but fails to improve the reliability under high load due to the significantly increased capacity requirement which leads to congestion and packet drop. Second, at the transport layer, the use of pure FEC can significantly improve the reliability, increasing PDR up to 100% in many cases, but can be inefficient in terms of the number of redundant packets transmitted. In contrast, a carefully designed ARQ–FEC hybrid protocol, such as RMDP, can also offer 100% reliability while improving the efficiency by up to 38% compared to a pure FEC scheme. To our best knowledge, this is the first in-depth study of high-throughput, reliable multicast protocols that provide 100% PDR for wireless mesh networks.     

Performance evaluation of high speed TCP over optical burst switching networks

Study of TCP performance over OBS networks has been an important problem of research lately and it was found that due to the congestion control mechanism of TCP and the inherent bursty losses in the Optical Burst Switching (OBS) network, the throughput of TCP connections degrade. On the other hand, High Speed TCP (HSTCP) was proposed as an alternative to the use of TCP in high bandwidth-delay product networks. HSTCP aggressively increases the congestion window used in TCP, when the available bandwidth is high and decreases the window cautiously in response to a congestion event. In this work, we make a thorough simulation study of HSTCP over OBS networks. While the earlier works in the literature used a linear chain of nodes as the network topology for the simulation, we use the popular 14-node NSFNET topology that represents an arbitrary mesh network in our study. We also study the performance of HSTCP over OBS for different bandwidths of access networks. We use two different cases for simulations where in the first HSTCP connections are routed on disjoint paths while in the second they contend for resources in the network links. These cases of simulations along with the mesh topology help us clearly distinguish between the congestion and contention losses in the OBS network and their effect on HSTCP throughput. For completeness of study, we also simulate TCP traffic over OBS networks in all these cases and compare its throughput with that of HSTCP. We observe that irrespective of the access network bandwidth and the burst loss rate in the network, HSTCP outperforms TCP in terms of the throughput and robustness against multiple burst losses up to the expected theoretical burst loss probability of 10⁻³.