光分组交换网络中光纤延迟线缓存技术

光分组交换网是全光网络发展的必然趋势.然而,光分组交换网络发展的瓶颈是光缓存技术.目前,在光域比较现实的还是采用光纤延迟线(FDL)作光缓存.重点研究了光纤延迟线光缓存技术,对FDL光缓存技术进行了深入的分析和归纳,并对每一种光纤延迟线光缓存调度策略的优缺点都进行了细致的分析.最后指出了光纤延迟线光缓存技术的未来研究重点和发展方向.     

A burst loss probability model with impatient customer feature for optical burst switching networks

We consider optical delay line buffer as a solution to reduce the number of lost burst in optical burst switching, one of the promising candidates for future networks. Such network takes burst loss as an important performance criteria in the design step. Network performance, however, cannot be captured efficiently using traditional queueing models, because they often ignore the impatience of messages traveling through optical switches which is one of the popular issues in communication networks. In this paper, we develop an analytic model for this system using queueing theory and considering special impatience features. Simulation results show that (i) the developed model with impatience features can decrease burst loss probability ( ? 10%) compared with other approaches, and (ii) applying that model, we demonstrate that shared buffer architecture in optical burst switching network with optical buffer often achieves lower burst loss probability than dedicated buffer way in several different scenarios. Copyright © 2014 John Wiley & Sons, Ltd.     

基于网络层的核心路由器缓存容量分析

目前对路由器缓存容量的分析，忽略了网络元素间的相互作用。从网络层的角度．全面引入TCP链路上各路由器的作用，为TCP链路建立一种新模型。采用隔离方法对核心路由器部分进行分析．得出核心路由器一个接口的缓存容量需求下界值，表明目前的光缓存技术下可实现高性能全光核心路由器。仿真实验结果验证了结论的正确性。     

HYPASS: an optoelectronic hybrid packet switching system

An architecture is presented for an optoelectronic hybrid packet switching system (HYPASS) for the distribution of multiple-bit-rate broadband services. HYPASS is based on an input-buffered/output-controlled arbitration protocol. The internal routing and interconnection utilizes a passive optical transport network with wavelength-tunable laser transmitters and fixed wavelength receivers. The single-stage multiwavelength optical interconnect provides an internally nonblocking network for large throughput routing of the bit-serial optical signals. An internal optical control network, with fixed-wavelength trouble receivers, sends output port information to the input nodes for arbitration and control. Packet buffer storage and control processing is performed by word-parallel electronic circuitry. The characteristics and device requirements for this design are presented along with results of a performance analysis of the arbitration and control protocol     

光总线交换网络输出排队两级缓冲结构与性能分析

为了解决核心路由器高速无阻塞光总线交换网络体系结构中的高速大容量分组缓冲这一关键技术难题,本文提出了基于SRAM技术和DRAM技术相结合的输出排队分组两级缓冲结构及相关LBF-MMA存储器管理算法,并利用实测的网络流量数据对该缓冲技术的性能进行了仿真分析.分析表明,两级缓冲结构较好地解决了光总线交换网络中分组缓冲高速度与大容量之间的矛盾,对高速路由器技术的发展也具有一定的指导意义.     

组播技术及其在光层的实现

带宽密集型的多媒体应用对现有网络提出了新的要求,组播技术有助于解决其在网络带宽和服务质量方面的问题,而在光层实现组播具有更简单、高效的特点.然而,光层组播由于光缓存、光分束和光波长变换等光器件的限制,呈现出和IP层组播不同的特点.对IP层和光层组播进行了讨论,分析了光层组播模型,并对稀疏光分束和稀疏波长变换的光网络组播路由提出了重路由到源和重路由到相关节点两种重路由方式.     

A low cost optical storage server for near video-on-demand systems

A near video-on-demand system is one of the most economic and practical applications to provide high quality digital video services through a network in terms of cost, storage and network capacity requirements. In this paper, an optical storage server with a novel data placement and retrieval schemes is proposed for a near video-on-demand system. The proposed data placement scheme on the optical discs fully exploits the periodical broadcast characteristic of an NVOD service to optimize the disc bandwidth utilization. By further applying our retrieval schedule strategy, the buffer requirement of a system can be significantly reduced. In that way, the maximal number of supported streams with the minimal buffer requirement can be easily achieved, The storage system can be applied not only to CD-ROMs storing MPEG-1, but also to Digital Video Disks (DVDs) storing MPEG-2 in the near future     

图压缩优化光组播最小网络编码路由

将网络编码和光网络相结合可以有效解决光网络的 带宽资源利用率等问题。然而,在光网络中进行编码操作,又将增加光网的光域运算开销、 复杂度和缓存需求。为了减少光网络中网络编码的操作次数,本文提出一种基于图压缩的方 法优化光网络拓扑结构, 结合智能优化遗传算法(GA)实现组播最大速率的光组播最小编码节点,通过对光网络拓扑结 构中的一类特殊潜在编码节点 进行压缩处理,达到缩小算法搜索空间、排除大量非最优解的目的。仿真结果表明,通过本 文图压缩优化后的光网络拓扑结 构,可以使得现有的智能优化GA在求解光组播最小网络编码路由问题时效率更高,寻找到的 解更优。     

网络服务器系统与新型光突发交换网络解决方案

随着用户带宽超摩尔定律增长、传输链路容量的迅猛增加,节点服务器系统能力成为制约网络容量增长的主要瓶颈。网络业务的发展趋势不会坐等高性能光子器件的成熟和实用化,可以预见未来10—20年内光子器件瓶颈将制约着新型光网络节点能力提高。文蕈将网络分成接入、节点和链路3个网络服务器系统,提出一种全新的光网络体系架构——基于服务的光网络体系架构,通过一个隐函数从网络代价、能耗和容量等角度定性考察各服务器系统对网络性能的影响。由此提出了双光纤链路与IP插空联合的光突发交换解决方案,以缓解光子器件瓶颈的限制。     

Packet delay in optical circuit-switched networks

A framework is provided for evaluation of packet delay distribution in an optical circuit-switched network. The framework is based on a fluid traffic model, packet queueing at edge routers, and circuit-switched transmission between edge routers. Packets are assigned to buffers according to their destination, delay constraint, physical route and wavelength. At every decision epoch, a subset of buffers is allocated to end-to-end circuits for transmission, where circuit holding times are based on limited and exhaustive circuit allocation policies. To ensure computational tractability, the framework approximates the evolution of each buffer independently. "Slack variables" are introduced to decouple amongst buffers in a way that the evolution of each buffer remains consistent with all other buffers in the network. The delay distribution is derived for a single buffer and an approximation is given for a network of buffers. The approximation entails finding a fixed point for the functional relation between the "slack variables" and a specific circuit allocation policy. An analysis of a specific policy, in which circuits are probabilistically allocated based on buffer size, is given as an illustrative example. The framework is shown to be in good agreement with a discrete event simulation model.     

Routing and time-slot assignment in optical TDM networks

Optical time-division multiplexing (O-TDM) networks can provide a finer bandwidth granularity than wavelength-division multiplexing networks, and will play an important role in future all-optical networks. Since optical buffers are expensive, a small buffer size will be the characteristic of O-TDM systems. This paper analyzes the problem of routing and time-slot assignment in O-TDM networks. The results lead to the proposal of a Dijkstra-like shortest-path routing scheme that intends to maximize the performance of an optical network with a small number of optical buffers. Performance evaluation of the proposed scheme is also presented.     

Packet scheduling algorithms and performance of a bufferedshufflenet with deflection routing

In a multihop network, packets go through a number of hops before they are absorbed at their destinations. In routing to its destination using minimum path, a packet at a node may have a preferential output link (the so-called “care” packet) or may not (the so-called “don't care” packet). Since each node in an optical multihop network may have limited buffer, when such buffer runs out, contention among packets for the same output link can be resolved by deflection. In this paper, we study packet scheduling algorithms and their performance in a buffered regular network with deflection routing. Using shufflenet as an example, we show that high performance (in terms of throughput and delay) can he achieved if “care” packets can be scheduled with higher priority than “don't care” packets. We then analyze the performance of a shufflenet with this priority scheduling given the buffer size per node. Traditionally, the deflection probability of a packet at a node is solved from a transcendental equation by numerical methods which quickly becomes very cumbersome when the buffer size is greater than one packet per node. By exploiting the special topological properties of the shufflenet, we are able to simplify the analysis greatly and obtain a simple closed-form approximation of the deflection probability. The expression allows us to extract analytically the performance trend of the shufflenet with respect to its buffer and network sizes. We show that a shufflenet indeed performs very well with only one buffer, and can achieve performance close to the store-and-forward case using a buffer size as small as four packets per node     

Performance of two-stage shared fiber delay line optical packet switch under bursty traffic

Packet contention is a major issue in an optical packet switching network. It is not a trivial task to resolve contention due to lack of optical RAM technology. This article proposes a two-stage shared fiber delay line (FDL) optical packet switch for contention resolution. In this article, shared FDLs are used to buffer optical packets, in which a pool of buffer memory is shared among all switch output ports. Most of the existing optical buffering schemes are output-based which require a huge number of FDLs as well as a larger switch size that incur extra implementation cost. However, a shared buffering approach is considered in this article in order to reduce implementation cost. In this article, FDLs are implemented in two stages using an extremely simple auxiliary switch. The proposed switch architecture leads to more efficient use of buffer space. The superiority of the proposed switch architecture has been established by means of extensive simulations. The performance of the proposed switch is investigated under bursty traffic. Simulation result shows that the proposed switch can achieve satisfactory performance at the price of a reasonable amount of FDLs. Moreover, the significance of the proposed switch is confirmed by simulation.     

Enhanced Dynamic Bandwidth Allocation Algorithm in Ethernet Passive Optical Networks

As broadband access is evolving from digital subscriber lines to optical access networks, Ethernet passive optical networks (EPONs) are considered a promising solution for next generation broadband access. The point‐to‐multipoint topology of EPONs requires a time‐division multiple access MAC protocol for upstream transmission. In this paper, we propose a new enhanced dynamic bandwidth allocation algorithm with fairness called EFDBA for multiple services over EPONs. The proposed algorithm is composed of a fairness counter controller and a fairness system buffer in the optical line terminal. The EFDBA algorithm with fairness can provide increased capability and efficient resource allocation in an EPON system. In the proposed EFDBA algorithm, the optical line termination allocates bandwidth to the optical network units in proportion to the fairness weighting counter number associated with their class and queue length. The proposed algorithm provides efficient resource utilization by reducing the unused remaining bandwidth made by idle state optical network units.     

Continuously Tunable, Wavelength-Selective Buffering in Optical Packet Switching Networks

This letter investigates system performance of slow-light variable optical buffer based on cascaded stages of tunable silica microresonator rings. Continuous tunability is achieved by adjusting the resonance of each ring on the compact photonic integrated circuit. The all-pass configuration allows selectively applying variable delays to wavelengths of choice without losing any packets in an optical packet switching network.     

单波长光缓存的研究与分析

对异步光突发交换网络中单波长光缓存进行仿真建模并辅以分析,介绍了当前已有的理论并用其验证仿真结果。用不同的信道资源分配算法进行仿真并比较结果,指出光缓存中缓存粒度最佳值的设置不仅和突发包的平均长度以及负载有关,而且与核心结点所采用的调度算法有关。     

A two-level stochastic approximation for admission control andbandwidth allocation

In an access node to a multiservice network [e.g., a base station in an integrated services cellular wireless network or the optical line terminal (OLT) in a broad-band passive optical network (PON)], the output link bandwidth is adaptively assigned to different users and dynamically shared between isochronous (guaranteed bandwidth) and asynchronous traffic types. The bandwidth allocation is effected by an admission controller, whose goal is to minimize the refusal rate of connection requests as well as the loss probability of cells queued in a finite buffer. Optimal admission control strategies are approximated by means of backpropagation feedforward neural networks, acting on the embedded Markov chain of the connection dynamics; the neural networks operate in conjunction with a higher level bandwidth allocation controller which performs a stochastic optimization algorithm. The case of unknown, slowly varying input rates is explicitly considered. Numerical results are presented that evaluate the approximation and the ability to adapt to parameter variations     

Experimental characteristics of optical crosspoint switch matrix and its applications in optical packet switching

This paper presents the experimental results of the switching performances of the fast reconfigurable optical crosspoint switch (OXS) matrix. This paper demonstrates unicast optical packet switching for a 10-Gb/s payload at various modulation formats and a 155-Mb/s nonreturn-to-zero label. Reconfigurable time as fast as 2 ns is achieved because of the optimized control circuit and device fabrication. The power and wavelength dependence for the payload and the capability of multihop operation are investigated as well. The functionalities of the OXS acting as an optical switch and an optical buffer are demonstrated in the optical network node experiment. Very good switching property is obtained for the OXS, which clearly validates OXS as a potential technique for future high-speed Internet-protocol-over-wavelength-division-multiplexing networks.     

未来光因特网中的光交换方式及其发展趋势

Internet的业务流量正以每六个月翻一番的速度快速增长,未来网络中,数据业务超过话音业务只是时间问题,因此,基于电路交换的电信网升级到支持基于分组交换的数据业务是不可避免的,但是对因特网来说,由于光逻辑与光存储等器件不成熟,发展全光分组交换,技术上异常困难。另一方面,近来新提出的光突发交换,技术上相对简单,性能特点优异,因而成为更理想的选择,本文介绍了全光分组交换和光突发交换的研究现状,比较了两者的优缺点,最后指出改进光突发交换性能的两种方式。