TCP over OBS边缘节点重传机制的研究

使用传输控制协议(TCP)的拥塞控制机制在传统互联网技术中是解决问题的很好方法.然而在面对新型的光网络技术OBS网络,简单地采用TCP技术因受到OBS自身特性的影响,性能表现不佳,吞吐量低下.为此,通过对OBS技术和TCP拥塞控制机制深入的研究,提出一种基于OBS边缘节点的ACK重传机制来提升TCP over OBS性能的方法,提高OBS网络吞吐量.     

OBS网络的TCP性能分析与改进

光突发交换(OBS，Optical Burst Switch)是下一代IP-over-DWDM光网络最有前途的解决方案之一。Burst组装算法和数据通道调度算法是OBS网络的关键技术，TCP协议是当前主要的传输层协议。该文对OBS网络的TCP性能进行分析，并提出了基于源地址集的组装算法和ACK优先调度算法。仿真结果表明使用该算法可以显著改善OBS网络的TCP性能。     

光突发交换网络的动态TCP特性研究

通过仿真研究了动态业务竞争环境下,不同TCP版本在OBS网络中的传输性能。研究中,以TCP在OBS网络中传送一个固定大小的文件所需的时间作为性能指标,此外,详细分析了突发丢失的内部机制和造成不同TCP版本性能差异的原因。结果表明,TCP SACK性能最好。     

光突发交换(OBS)网络TCP性能改善

介绍光突发的基本原理及影响OBS网络TCP性能的一些因素，并针对TCP性能的改善的两种方法进行了详细说明，提出了一种改进策略。     

基于NSE的OBS网络公平性研究

分析了TCP流量和UDP流量接入OBS网络的公平性,并提出了一种新的公平性机制：在OBS边缘节点处将TCP分组和UDP分组分别组包,并在核心节点处实行保护TCP分组的丢包策略,有效提高了OBS网络的公平性。在此基础上扩展和改进了原有一台计算机进行NS仿真软件的Emulation功能,搭建了四台计算机构成的联合仿真（Joint Emulation）平台,将真实网络负载分别通过四台计算机中端接入仿真环境中的OBS网络。得到了更加逼近真实的OBS实验数据,有效验证了公平机制和丢包策略。     

光突发交换网络中的传输控制协议性能

光突发交换(OBS)是IP over WDM核心网络采用的交换技术。在OBS网络中,送往同一边缘节点的IP分组汇聚成传输和交换的基本单元———数据突发(DB),DB丢弃会导致大量IP分组丢失,显著影响传输层的性能。文中分析OBS网络的参数对传输控制协议(TCP)吞吐量和时延的影响。仿真结果表明,DB丢包率越高,TCP性能越差。在低丢包率情况下,随着DB长度的增加,TCP吞吐量和端到端时延明显增加,高丢包率情况下则不明显;随着汇聚周期的增加,TCP吞吐量逐渐下降,端到端时延逐渐增加。     

光网络中的TCP混沌特性仿真分析

为了研究OBS网络的TCP非线性行为特性，本文利用Markov链模型，通过计算TCP窗口序列的Lyapunov指数，分析了影响TCP混沌特性的因素，以及这些因素对混沌特性的作用方式。仿真结果表明，OBS网络的TCP窗口非线性变化行为具有混沌特性，网络丢突发包率、突发包封装周期、TCP流速率以及最大拥塞窗口长度都会对TCP混沌特性产生影响。     

光分组交换网的TCP性能研究

与传统光网络相比,光分组交换(OPS)网络具有高速、大吞吐量、低时延和能高效地承载IP业务等突出优点.而作为支撑下一代Internet发展的最有希望的骨干光网络,OPS网与传输控制协议/互联网协议(TCP/IP)的兼容性和支持度是一个值得深入研究的课题.文章以光突发交换(OBS)网为模型,对OPS网络中的TCP传输性能进行了研究.     

光突发交换网络中TCP Reno 的性能分析

该文在分析光突发交换(OBS)网络对TCP性能影响的基础上,研究了单个突发所包含的属于同一TCP/ IP连接的分组数对TCP Reno吞吐量性能的影响,得到了一个吞吐量与突发丢失率、单个突发所包含分组数以及往返时延(RTT)的闭合表达式;并通过仿真验证了分析的正确性;分析和仿真结果表明,在接入链路带宽较大时,突发所包含的分组数存在一个最佳值,使TCP吞吐量达到最大。     

OBS环网竞争解决办法的分析和比较

在光突发交换(OBS)基本概念的基础上,针对OBS网络,特别是OBS环网突发包竞争引起的突发包丢包等问题,介绍和比较了OBS网络中常用的突发包竞争解决办法.重点分析了几种适用于OBS环网的常用突发包竞争解决办法对网络吞吐量等主要性能的影响,指出了采用这几种竞争解决办法的网络的性能优劣,归纳总结了它们的优缺点.     

TCP over optical burst-switched networks with controlled burst retransmission

For optical burst-switched (OBS) networks in which TCP is implemented at a higher layer, the loss of bursts can lead to serious degradation of TCP performance. Due to the bufferless nature of OBS, random burst losses may occur, even at low traffic loads. Consequently, these random burst losses may be mistakenly interpreted by the TCP layer as congestion in the network. The TCP sender will then trigger congestion control mechanisms, thereby reducing TCP throughput unnecessarily. In this paper, we introduce a controlled retransmission scheme in which the bursts lost due to contention in the OBS network are retransmitted at the OBS layer. The OBS retransmission scheme can reduce the burst loss probability in the OBS core network. Also, the OBS retransmission scheme can reduce the probability that the TCP layer falsely detects congestion, thereby improving the TCP throughput. We develop an analytical model for evaluating the burst loss probability in an OBS network that uses a retransmission scheme, and we also analyze TCP throughput when the OBS layer implements burst retransmission. We develop a simulation model to validate the analytical results. Simulation and analytical results show that an OBS layer with controlled burst retransmission provides up to two to three orders of magnitude improvement in TCP throughput over an OBS layer without burst retransmission. This significant improvement is primarily because the TCP layer triggers fewer time-outs when the OBS retransmission scheme is used.     

Reducing the impact of false time out on TCP performance in TCP over OBS networks

Random burst contention losses plague the performance of Optical Burst Switched networks. Such random losses occur even in low load network condition due to the analogous behavior of wavelength and routing algorithms. Since a burst may carry many packets from many TCP sources, its loss can trick the TCP sources to conclude/infer that the underlying (optical) network is congested. Accordingly, TCP reduces sending rate and switches over to either fast retransmission or slow start state. This reaction by TCP is uncalled-for in TCP over OBS networks as the optical network may not be congested during such random burst contention losses. Hence, these losses are to be addressed in order to improve the performance of TCP over OBS networks. Existing work in the literature achieves the above laid objective at the cost of violating the semantics of OBS and/or TCP. Several other works make delay inducing assumptions. In our work, we introduce a new layer, called Adaptation Layer, in between TCP and OBS layers. This layer uses burst retransmission to mitigate the effect of burst loss due to contention on TCP by leveraging the difference between round trip times of TCP and OBS. We achieve our objective with the added advantage of maintaining the semantics of the layers intact.     

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.     

在OBS网络中改进TCP性能的高效机制

Transmission Control Protocol (TCP) performance over Optical Burst Switching (OBS) is experimentally investigated on an OBS network testbed, concluding that burst losses will lead to a significant drop in the available TCP bandwidth. Two mechanisms are introduced to improve TCP performance. One is concerning the burst assembly optimization and another is based on the novel assembly and scheduling mechanism to reduce the burst losses.     

Source-ordering for improved TCP performance over load-balanced optical burst-switched (OBS) networks

Recent advances in optical switching technology allow for the creation of networks in which data bursts are switched optically at each node, offering a greater degree of flexibility suitable for handling bursty Internet traffic. TCP-based applications account for a majority of data traffic in the Internet; thus understanding and improving the performance of TCP implementations over OBS networks are critical. Previously, several articles show that load-balanced routing improves loss-performance in OBS. In this paper, we identify the ill-effects of load-balanced OBS on TCP performance caused by false time-outs and false fast-retransmits. We propose a source-ordering mechanism that significantly improves TCP throughput over a load-balanced OBS network.     

Multi-layer loss recovery in TCP over optical burst-switched networks

It is well-known that the bufferless nature of optical burst-switching (OBS) networks cause random burst loss even at low traffic loads. When TCP is used over OBS, these random losses make the TCP sender decrease its congestion window even though the network may not be congested. This results in significant TCP throughput degradation. In this paper, we propose a multi-layer loss-recovery approach with automatic retransmission request (ARQ) and Snoop for OBS networks given that TCP is used at the transport layer. We evaluate the performance of Snoop and ARQ at the lower layer over a hybrid IP-OBS network. Based on the simulation results, the proposed multi-layer hybrid ARQ + Snoop approach outperforms all other approaches even at high loss probability. We developed an analytical model for end-to-end TCP throughput and verified the model with simulation results.     

Using multiple per egress burstifiers for enhanced TCP performance in OBS networks

Burst assembly mechanism is one of the fundamental factors that determine the performance of an optical burst switching (OBS) network. In this paper, we investigate the influence of the number of burstifiers on TCP performance for an OBS network. The goodput of TCP flows between an ingress node and an egress node traveling through an optical network is studied as the number of assembly buffers per destination varies. First, the burst-length independent losses resulting from the contention in the core OBS network using a non-void-filling burst scheduling algorithm, e.g., Horizon, are studied. Then, burst-length dependent losses arising as a result of void-filling scheduling algorithms, e.g., LAUC-VF, are studied for two different TCP flow models: FTP-type long-lived flows and variable size short-lived flows. Simulation results show that for both types of scheduling algorithms, both types of TCP flow models, and different TCP versions (Reno, Newreno and Sack), TCP goodput increases as the number of burst assemblers per egress node is increased for an OBS network employing timer-based assembly algorithm. The improvement from one burstifier to moderate number of burst assemblers is significant (15–50% depending on the burst loss probability, per-hop processing delay, and the TCP version), but the goodput difference between moderate number of buffers and per-flow aggregation is relatively small, implying that an OBS edge switch should use moderate number of assembly buffers per destination for enhanced TCP performance without substantially increasing the hardware complexity.