Analytical models of blocking probability for multi-granularity cross-connect-based optical networks

Multi-granularity optical cross-connect (MG-OXC)-based optical network is a promising optical network architecture as it is capable of flexible switching at different granularity levels. In MG-OXC-based optical networks, wavelength conversion (WC) capability and the number of usable add/drop ports of the nodes are two key factors affecting its performance. Two analytical models of blocking probability for MG-OXC-based optical networks both without WC capability and with sparse WC capability are proposed, exploiting Erlang?s loss formula and birth?death process. Based on the models and simulation, the impact of WC capability and the number of add/drop ports on the blocking probability are investigated. Three kinds of granularities (i.e. fibre, waveband and wavelength) are considered in MG-OXC nodes to reduce the complexity and size of switch fabric. Both the analytical and simulation results are given on two network topologies under dynamic traffic patterns. Simulation results show that the proposed models are accurate and effective for the analysis of blocking probability in MG-OXC-based optical networks.     

多波长光网络的动态路由等效算法

针对多波长光网络的特点，提出了一种动态路由和波长分配的等效算法。采用波长图、增加虚拟源节点和目的节点等技术，把多波长网络转化为等效的单波长网络，避免了求解路由和波长分配两个复杂子问题，简化了算法的程序设计。利用最短径算法进行路由和波长分配可以求得问题的最优解，从而有效地降低了网络阻塞率。仿真结果表明：与FAR-2D算法相比，在4和8波长的全波长转换网络中，采用等效算法阻塞率最大降幅分别达到0．02、0．025。     

稀疏波长变换的WDM光网络阻塞率的分析与计算

本文主要对具有稀疏波长变换的WDM全光网的阻塞率进行分析,首先提出一种模型分析了无波长变换器的L跳路径端到端阻塞率,接着对部分波长变换器的L跳路径的阻塞率进行求解,随后分析了全网的平均阻塞率。研究得到的主要结论是,波长变换器使用的有效性取决于网络的连接度。     

一种新型的动态路由和波长分配综合算法

讨论了WDM光网中，在动态业务流量和有限范围波长变换情况下的动态路由和波长分配问题。基于Moone-Dijkstra算法，考虑到动态波长变换的可能和限制，提出了一种新型的、可实现动态最小代价路由和最佳虚波长通道的综合启发式算法(DMC-OVWP)。该算法对路由子问题和波长分配子问题既相互独立，又相互结合，优化了RWA。以中国教育和科研计算机网(CERNET)为拓扑背景，基于本算法进行了计算机仿真，并对实验结果进行了比较分析，证明本算法可充分利用网络信息获取较低的阻塞率。     

Reactive and proactive routing in labelled optical burst switching networks

Optical burst switching architectures without buffering capabilities are sensitive to burst congestion. The existence of a few highly congested links may seriously aggravate the network throughput. Proper network routing may help in congestion reduction. The authors focus on adaptive routing strategies to be applied in labelled OBS networks, that is, with explicit routing paths. In particular, two isolated alternative routing algorithms that aim at network performance improvement because of reactive route selection are studied. Moreover, a nonlinear optimisation method for multi-path source-based routing, which aims at proactive congestion reduction is proposed. Comparative performance results are provided and some implementation issues are discussed.     

部分波长光网络中的动态波长分配算法

为适应网络中不同服务质量（QoS）的光路建立请求具有不同的优先级的情况,提出了一种用于部分波长可变网络中支持QoS的动态波长分配算法。该算法对网络中的业务请求分高、低两个优先级进行处理。对于高优先级的光路建立请求,通过充分利用网络中已配置的波长转换器实时改变可用波长集,以降低高优先级业务请求的阻塞率。对低优先级的光路建立请求,只考虑所选路径的当前位置是否有波长转换器来改变可用波长集,保证了低优先级的光路建立请求速度。仿真结果表明,该算法既能保证较高优先级的光路建立请求具有较低的阻塞率,又充分利用了有限的网络资源,实现了对波长转换器的最优利用。     

双光纤波分复用网阻塞率研究

研究了双光纤波分复用互联网在不同网络容量使用率时的阻塞率,主要对单光纤网络使用波长变换器和双纤网络在波长数不同时对网络阻塞率的改善情况做了仿真比较,结果表明仅仅在低阻塞率时波长变换器给网络所带来的增益非常有限,双纤网络可以达到其效果。     

Asymmetric convolution algorithm for blocking probability calculation in full-availability group with bandwidth reservation

The paper proposes a new approximate calculation method of occupancy distribution and blocking probability in the full-availability group (FAG) with multi-rate traffic streams and bandwidth reservation. The algorithm involves calculation of system state probabilities by a convolution operation. In the paper, an effective method of calculating state probabilities in a reservation space of the system is derived. The analytical results of blocking probabilities in the FAG with bandwidth reservation, obtained on the basis of the proposed analytical method, are compared with the data obtained on the basis of other known analytical methods and with the simulation results. The accuracy of the proposed method is evaluated for different multi-rate Bernoulli (Erlang), Poisson (Engset), Pascal traffic streams. The method proposed is characterised by lower complexity than the convolution algorithm for the FAG with bandwidth reservation devised earlier.     

Dimensioning for in-band and out-of-band signalling protocols in OBS networks

Most of the previous works on optical burst switching (OBS) assume in their analysis that signalling does not affect network performance. It is analysed here, under which conditions the effect of signalling is actually negligible, taking into account the effect of signalling in the evaluation of burst discard probability. First, analytical models for two different signalling approaches in an OBS network are presented: `out-of-band? and `in-band? techniques. The impact of these two signalling strategies in terms of the probability of burst discard are evaluated, identifying the component of bursts discarded as a consequence of control message losses or of excessive signalling delay. A new method is also discussed, based on the previous models, to assign the correct amount of resources to the control plane. To verify the accuracy of the analytical results, these are compared with results based on discrete-event simulationns: results are found to be in a highly satisfactory agreement with simulations.     

波长路由在并行计算机光互连中的应用

提出了一种波长路由并行光互连技术，其路由直接在源端用目标地址选择波长来建立，各波长有独立传输路径并采用光通道复用，路由变换节点为全光结构，光信号在变换节点处无转发延迟。此技术可应用于并行计算机互连网络和分布式高性能计算机群的互连网络。     

一种新型IP OVER WDM城域网的节点结构

提出了一种基于波分复用（WDM）,分组交换,副载波复用和波长变换技术的新型全光城域网节点结构,网络拓扑采用环形,网络节点采用可调输出固定输入的选波原则以利于数据的多重接入,副载波复用和基于级联半导体光放大器的波长变换,实现了射频副载波路由信息与基带IP数据包的同步复用和IP数据包的透明传输。     

Selective assign shortest path first algorithm for routing and wavelength assignment in the presence of four wave mixing

The authors proposed a selective assign shortest path first (SASPF) algorithm for routing and wavelength assignment in the presence of four wave mixing (FWM) in wavelength division multiplexing network with a design parameter V_m. In order to maintain a reasonably good performance in terms of blocking probability to fulfil the connection requests but also to allow acceptable FWM effects, V_m is an important design parameter (number of established optical channels to fulfil the connection requests but also to allow acceptable FWM effects). If its value is too low, many connection requests will not be able to establish, which may lead to higher blocking probability. On the other hand, if its value is too high, it may lead to obvious FWM effects that will affect the network performance. Thus, V_m must be optimum to balance the requirement of the connection requests and also the induced FWM crosstalks. Performance results show that SASPF algorithm outperforms the comparison scheme such as traditional assign shortest path first resulting in low blocking probability with a specific value of V_m.     

The designs of a scalable optical packet switching architecture

Abstract

This paper proposes a new switching architecture to be used in all optical packet switching networks. The proposed switch is derived from an original 2 × ?2 two‐stage multi‐buffer switched delay line based optical switching node, known as an M‐Quadro node. By incorporating bypass lines into the M‐Quadro architecture and employing a novel switch control strategy, the optical packet switching node can effectively resolve packet contentions, thus reducing the packet deflection probability substantially. Furthermore, we show that such architecture is scalable for a generic multiple stages optical packet switch with a larger number of input/output ports.     

Load-balanced wavelength assignment strategies for optical burst/packet switching networks

Loss-free schemes are defined to ensure successful packet/burst transmissions in optical packet/burst switching networks. To this end, they rely on a collision-free routing and wavelength assignment (CF-RWA) scheme combined with simple contention resolution mechanisms that guarantee the absence of losses in intermediate links. Here, the CF-RWA problem is studied. In particular, by using graph theory, the problem of finding CF-RWA schemes that minimise the number of wavelengths to serve a given traffic matrix is set. The problem is simplified when it is formulated by using pre-defined sets of non-colliding paths. Within this framework, the problem is shown to be equivalent to finding a given vertex-set colouring of the so-called restriction digraph. Here, two heuristic algorithms are proposed to obtain such vertex-set colourings. One of them provides a suitable CF-RWA without having to solve the minimisation problem. By way of example, the proposed method is applied to the NSFNet and the EON network providing quasi-optimal results.     

Serialised batch scheduling algorithm for optical burst switching networks

A new scheduling algorithm called serialised batch scheduling (SBS) for optical burst switching (OBS) networks is proposed. SBS aggregates and serialises bursts along a shared path into one composite burst, which is switched as one unit. There are two major processes in SBS, namely, batching and serialising. While the batching process chooses a set of bursts to form the composite burst, the serialising process determines how to organise the OBS bursts within the composite burst and generates a corresponding control packet for this burst. Several SBS batching and serialising schemes are introduced and analysed here. The study by the authors shows that the guard band and burst overlap can be reduced in the SBS and, thus, the packet loss rate and the number of switch reconfigurations can be significantly reduced. In addition, it is indicated that the proposed SBS algorithm can be coupled with other OBS scheduling algorithms and reduce the requirements for a high-speed optical switch in OBS networks.     

Dynamic O-band to C-band wideband wavelength converter for integrated VCSEL-based optical interconnects

ABSTRACT

Real-time wavelength conversion and traffic routing at key network nodes is a fundamental requirement for current optical interconnects. This work experimentally demonstrates a broadband wavelength conversion from O-band to C-band employing commercially available, power efficient VCSELs. A 1310?nm VCSEL is directly modulated with 8.5 Gbps data and transmitted over 22?km G. 652 fibre with a 0.53 dB penalty. The received data is used to run a 1550?nm VCSEL located at the network integration node, achieving the first reported wavelength conversion from O-to-C-band. VCSEL wavelength tuneability with changing bias current functionality is further exploited to route the converted wavelength over 400?GHz spectra range for integration into wavelength flexible networks. The newly converted wavelength is transmitted over 24.7?km of G. 655 fibre, incurring a maximum penalty of 1.86?dB. Results from this work proves an enabling development technology for wavelength converters for transparent contention resolution in current and future optical Interconnects.     

EAMTR: energy aware multi-tree routing for wireless sensor networks

IEEE 802.15.4 is the prevailing standard for low-rate wireless personal area networks. It specifies the physical layer and medium access control sub-layer. Some emerging standards such as ZigBee define the network layer on top of these lower levels to support routing and multi-hop communication. Tree routing is a favourable basis for ZigBee routing because of its simplicity and limited use of resources. However, in data collection systems that are based on spanning trees rooted at a sink node, non-optimal route selection, congestion and uneven distribution of traffic in tree routing can adversely contribute to network performance and lifetime. The imbalance in workload can result in hotspot problems and early energy depletion of specific nodes that are normally the crucial routers of the network. The authors propose a novel light-weight routing protocol, energy aware multi-tree routing (EAMTR) protocol, to balance the workload of data gathering and alleviate the hotspot and single points of failure problems for high-density sink-type networks. In this scheme, multiple trees are formed in the initialisation phase and according to network traffic, each node selects the least congested route to the root node. The results of simulation and performance evaluation of EAMTR show significant improvement in network lifetime and traffic distribution.     

Fault impact and fault tolerance in multiprocessor interconnection networks

Growing complexity of parallel machines coupled with increasing chip densities escalates the need for fault tolerance and recovery in these systems. In pursuit of the goal of fault-tolerant multiprocessors, many techniques have been proposed. Since methods for designing fault-tolerant processors and memories are relatively mature, the techniques considered in this paper focus on the interconnection network (ICN) linking the processors. The impact of faults on non-fault-tolerant ICNs is contrasted with that in fault-tolerant networks. Fault tolerance in ICNs is addressed at two levels, inter-node or switch level and system level. Inter-node or switch level pertains to data and control integrity and system level deals with maintaining network connectivity and adequate performance levels in the presence of faults. Fault-tolerant schemes at the switching element level warrant some form of concurrent error detection such as the use of codes usually combined with a full handshake protocol. Space–time trade-offs involved in the use of various codes and protocols are investigated. At the system level, several augmented multi-stage switching ICNs, tree and ring networks are studied. The combined provision for fault tolerance together with improved performance in the non-fault condition is emphasized. Finally, strategies for network reconfiguration and rerouting after system failure are presented.     

Contention minimisation in optical burstswitched networks combining traffic engineering in the wavelength domain and delayed ingress burst scheduling

A strategy for minimising the probability of contention in optical burst-switching (OBS) networks, by combining traffic engineering in the wavelength domain with delayed burst scheduling at the ingress nodes, has been proposed. The implementation of this strategy only requires an increase on the processing and electronic buffering capacities of the ingress nodes, while avoiding the use of complex and expensive optical buffers at the core nodes. The performance evaluation study has shown that the proposed strategy outperforms the burst-scheduling strategies described in the literature by several orders of magnitude, in terms of burst-blocking probability. Moreover, the performance improvements have been shown to depend on the average offered traffic load, number of wavelengths per link and maximum delay allowed at the ingress nodes.     

Software architecture design,implementation, and evaluation of DCF-based MAC protocol on a low-power transceiver

The carrier-sensing multiple access with collision avoidance (CSMA/CA) protocol is the most well-known medium access control (MAC) protocol for wireless networks. Both the distributed coordination function (DCF) defined in IEEE 802.11 and the MAC layer defined in IEEE 802.15.4 are based on the CSMA/CA protocol. Nevertheless, these two standards have quite different carrier-sensing mechanisms. Different to continuous carrier sensing in DCF, an IEEE 802.15.4 node only senses the channel once just after a backoff. Sensing-once mechanism can reduce the computation loading on the CPU. However, it significantly increases the probability of failure transmission because a node is not fully aware of channel activity. This paper first proposes a software architecture integrating proper hardware features for designing a DCF-based MAC protocol and then successfully implements it on a low-power transceiver. In addition, this paper conducts experiments in a star topology network to compare the performance of the above DCF-MAC protocol with the IEEE 802.15.4 MAC protocol. Experimental results show that, without continuous sensing, the IEEE 802.15.4 network suffers a high transmission failure probability as the network size increases. Consequently, the proposed DCF-based MAC protocol outperforms the IEEE 802.15.4 MAC protocol in terms of packet loss probability and throughput.