Pre-planned optical burst switched routing strategies considering the streamline effect

Optical burst switching is a promising paradigm for the next IP over optical network backbones. However, due to its bufferless nature, it can be highly affected by burst contention. Several methods have been proposed to address this problem, most of them without considering a phenomenon unique to optical burst switched networks called streamline effect. Most of the reported studies also assume the existence of total wavelength conversion capacity on all nodes, presently a very expensive and somewhat unrealistic configuration, and additionally, the contention resolution schemes adopted increase in the complexity of the core nodes, hampering scalability. In this study, we present a traffic engineering approach for path selection with the objective of minimizing the contention considering the streamline effect and using only topological information. The main idea is to balance the traffic across the network in order to prevent congestion while keeping simple the architecture of the core nodes and without incurring into link state dissemination penalties. We propose and evaluate the path selection strategies in both networks with full wavelength conversion capability and networks with imposed wavelength continuity constraint. Results show that our strategies can outperform the traditionally used shortest path routing.     

A framework of prioritized burst segmentation supporting controlled retransmission in OBS networks

In optical burst switching (OBS) networks, burst contentions in OBS core nodes may cause data loss. To reduce data loss, retransmission scheme has been applied. However, uncontrolled retransmission may increase network load significantly and data loss probability defeating the retransmission purpose. In addition, in a priority traffic existing OBS network, OBS nodes may apply different retransmission mechanisms to priorities bursts for quality-of-service (QoS) support. This study has developed a controlled retransmission scheme for prioritized burst segmentation to support QoS in OBS networks. Unlike previous works in the literature, we have set a different value to retransmission probability at each contention and propose a retransmission analytical model for burst segmentation contention resolution scheme. In addition, we have applied the proposed retransmission scheme to the prioritized burst segmentation for QoS support. We have taken into account the load at each link due to both fresh and retransmitted traffic, and have calculated the path blocking probability and byte loss probability (ByLP) for high-priority and low-priority burst to evaluate network performance. An extensive simulation has been proposed to validate our analytical model.     

Soft‐State Bandwidth Reservation Mechanism for Slotted Optical Burst Switching Networks

This paper proposes a novel transport network architecture for the next generation network (NGN) based on the optical burst switching technology. The proposed architecture aims to provide efficient delivery of various types of network traffic by satisfying their quality‐of‐service constraints. To this end, we have developed a soft‐state bandwidth reservation mechanism, which enables NGN transport nodes to dynamically reserve bandwidth needed for active data burst flows. The performance of the proposed mechanism is evaluated by means of numerical analysis and NS2 simulation. Our results show that the packet delay is kept within the constraint for each traffic flow and the burst loss rate is remarkably improved.     

OBS网络中一种基于突发包优先级分割的可控重传方案

在光突发交换(OBS)网络中,突发包会由于竞争OBS核心节点输出端口的有限波长资源而发生冲突。突发包重传能够在一定程度上减少由于突发包在核心节点冲突而导致的数据损失,但重传次数的增加可能会加重网络负荷,反而增加数据丢失率。并且,在多业务存在的OBS网络中,重传方案需要能够实现区分服务以保证网络的服务质量(QoS)。据此,本文提出一种基于突发包优先级分割的可控重传方案,在实施优先级分割的同时,根据网络负荷赋予每次重传不同的概率,并对重传次数加以控制。最后,仿真分析了路径阻塞率和不同优先级业务的字节丢失率(ByLP,byte loss probability)性能。     

Dynamic Deflection Routing with Virtual Wavelength Assignment in Optical Burst-Switched Networks

In optical burst-switched networks, one of the most significant issues is contention resolution. There have been several deflection routing techniques as contention resolution. While contention is resolved by traditional deflection routing, it cannot guarantee that the control packet will reserve all the wavelengths successfully to the destination on the alternate path, especially when traffic load in a network is high. Therefore, in this paper, we propose a Deflection Routing with Virtual Wavelength Assignment (DR-VWA) algorithm in order to provide a higher resource guarantee for loss-sensitive traffic bursts. The proposed DR-VWA scheme (1) dynamically decides the alternate path with the least traffic load and (2) allows high-priority bursts in terms of loss to be assigned available wavelengths over the path virtually. The proposed scheme is evaluated through simulation, and it is shown that significant improvement with regard to burst loss and wavelength conversion cost can be achieved.This work was supported in part by the Korea Science and Engineering Foundation (KOSEF) through OIRC project and by the US National Communications System (NCS).     

Parallel link server architecture: a novel contention avoidance mechanism in OBS networks

Optical burst switching (OBS) is thought to be the best way to adapt bursty traffic of IP-based next generation network services. However, there are a lot of challenges to make OBS networking a reality. Of most concern is burst contention avoidance. The major contention avoidance resolutions in literature are wavelength conversion, fiber delay lines, and deflecting routing. They are very vulnerable to network load and may suffer from severe data loss in case of heavy traffic. Even at moderate traffic, contention caused by using these methods lead to burst blocking and data losses. In this article, a novel contention avoidance technique is presented by using the parallel link server (PLS) architecture, which may overcome the lack of information at the edge node and the absence of global coordination among nodes. Using Poisson and Self-Similar traffic arrival models, the proposed mechanism is compared with the traditional single link server architecture through simulation in the 14-node national science foundation network. The numerical results show that this architecture, without additional other methods, can obtain burst blocking and data dropping probabilities with almost two orders of magnitudes less than those in the single link server architecture. Gains are achieved by less than 7% increase in end-to-end delay when carrying coordinated traffic and a load under 0.45.     

Priority‐Based Duplicate Burst Transmission Mechanism in Optical Burst Switching Networks

This paper proposes a priority‐based duplicate burst transmission mechanism in an optical burst switching network to enhance the probability of successful reception of bursts. The performance of the proposed mechanism is evaluated by NS2 simulations. Our results show that the burst loss rate is improved especially under light traffic loads.     

一种支持业务均衡的OBS自适应多可达性路由机制

针对光突发交换(OBS)网络中如何高效解决频繁发生的光突发竞争问题,提出了一种支持业务均衡的OBS自适应多可达性路由机制(AMR-LB).首先根据发送端发送业务量大小和当前网络业务承载状态,按需地为光突发确定多可达性路由;然后在非线性规划下,自适应地调整各条路由的业务承载比例.通过性能仿真,并与自适应替代路由算法(AA...     

OBS考虑优先级的突发包碎片可控合并重传算法

为了降低光突发交换网络中突发包的丢失率、降低网络路径的阻塞率、减小突发包冲突的概率,提出了考虑优先级的突发包碎片可控合并重传算法。当网络中数据通信发生冲突时,该算法能根据优先级进行突发包的分片,核心节点将这一信息反馈给边缘节点,边缘节点根据突发碎片的优先级以一定的概率重传被丢弃的突发包分片;同时,针对由于多次重传导致的突发包碎片过多的问题,该算法还按照突发包碎片的优先级顺序进行碎片重组,大大降低了网络的阻塞率。结果表明,相比以往的冲突解决算法,此算法在网络业务繁忙时的数据丢比特率和网络阻塞率方面的改善作用有比较明显的优势。这一结果对光突发交换网络的网络的性能改善方面是有帮助的。     

光突发交换网络新型偏射路由方案研究

光突发交换(OBS)被认为是下一代光网络中的有效核心交换技术之一,设计OBS网络的最初目的之一是减小突发包丢失率.解决突发竞争的方法主要包括光缓存、波长变换、偏射路由和突发分段.提出一种改进偏射路由方案,并建立了数学模型,对改进方案的性能进行了仿真分析,结果表明改进方案能更好的提高网络整体性能.     

Optimized Combination of Converter Pools and FDL Buffers for Contention Resolution in Optical Burst Switching

Optical burst switching (OBS) has attracted interest as a transport network architecture for the future optical Internet. As OBS relies on statistical multiplexing efficient contention resolution is a key issue in order to achieve a low burst loss probability. First, this paper discusses options and key design parameters for contention resolution in OBS. Then, it evaluates the performance of OBS nodes which employ shared wavelength converter pools and simple fiber delay line (FDL) buffers. Finally, optimized strategies for the order of probing a wavelength converter pool and an FDL buffer for contention resolution are presented and compared. It is shown that these strategies can be used to optimize performance for a given, for example, minimal cost, dimensioning of the wavelength converter pool and the FDL buffer.     

Contention-Based Limited Deflection Routing Protocol in Optical Burst-Switched Networks

Optical burst switching (OBS) is a very promising switching technology for realization of an economical optical Internet. In OBS networks, when contention occurs at an intermediate switch, two or more bursts that are in contention can be lost because a forwarding path reservation is not made for a burst until a control message for the burst arrives. That is the reason why one of the critical design issues in OBS is finding ways to minimize burst dropping resulting from resource contention. In this paper, we propose and analyze a novel deflection routing protocol, which mitigates and resolves contention with significantly better performance as compared with techniques currently known in the literature. While several variants of the basic deflection routing scheme have been proposed before, they all lacked the ability to determine the alternate route based on clear performance objectives. In this paper, we present an on-demand deflection routing scheme, which sequentially performs the following: 1) based on certain performance criteria, dynamically determines if the burst should be deflection routed or retransmitted from source and 2) if the decision is to deflection route, then the same is done using a path that is based on minimization of a performance measure that combines distance and blocking due to contention. The proposed contention-based limited deflection routing scheme prevents injudicious deflection routing. Our simulation results show that the scheme proposed here has much superior performance both in terms of burst loss probability and increased network throughput. Through analytical and simulation modeling, a number of useful insights into the OBS network protocols and performance are provided.     

光突发交换网中的智能组包研究

光突发交换(OBS)相对传统的电路交换方式具有更高的传输效率和更短的网络时延,而相对于未来网络的发展趋势光分组交换,光突发交换具备更现实的可行性.在OBS中,突发汇聚是一个很关键的技术,它对OBS网络的性能有着重要的影响,在本文中,我们对突发汇聚机制进行了较深入的研究,并提出了一种新的突发汇聚算法,它对抑制网络流量的自相似性,提高突发传输效率和避免在不同节点由于突发同步所引起的带宽资源竞争都有较好的结果.     

OBS网络中一种基于蚁群探测的路由机制

光突发交换技术是最具发展潜力的光交换技术之一,而减少突发丢失是其首要问题。传统的静态路由机制不能随着网络负载的变化而更改路由,不能有效应对动态业务。为此,在研究现有动态负载平衡路由机制的基础上,提出了一种基于蚁群探测的路由机制。蚁群根据节点出度链路上的负载变化选择下一跳节点,当转发到目的节点时收集蚁群探测到的所有备选路径,然后根据备选路径中记录的链路负载选择可使丢包最小的路径,通过选择更加合理的路由,达到减少突发丢失率的目的。仿真结果表明,与其他算法相比,所提出的机制表现出比较好的性能,有效降低至少15%突发丢失率。     

Design and performance comparison of multiple-token based MAC protocols for optical burst switched ring networks

Optical burst switching (OBS) has been proposed as a new optical switching paradigm for the next generation Internet due to its flexibility and feasibility compared to OCS and OPS. Moreover, serving as a backbone that interconnects a number of access networks, OBS ring topologies have been a good choice for solving the current metro gap problem between core network and access network owning to its simplicity and scalability. In this paper, we provide an insight into the OBS ring network that consists of nodes using TT–TR (Tunable Transmitter–Tunable Receiver). The node architectures with TT–TR may make efficient use of network resources even though traffic pattern, such as IP traffic with self-similarity dynamically change, and can support good expandability. However, all nodes share the limited network resources. This may result in contention such as wavelength contention and transceiver contention leading to burst loss. In order to use the shared network resources fairly and efficiently as well as reducing the resource contention, we focus on the design of medium access control (MAC) protocols based on multiple tokens. Each token is allocated to one wavelength to denote the accessibility of that wavelength, i.e., once the token is captured, the corresponding wavelength can be used to transmit a burst. As tokens hold the key for using wavelengths to transmit bursts, token management including the token release time is crucial in the proposed MAC protocols. Thus, two kinds of multiple-token based MAC protocols with different token release times are proposed: token release after transmitting burst (TRTB) and token release after transmitting control header (TRTC). Each of them is classified into two schemes called TRTB/TRR and TRTB/RCA and correspondingly TRTC/TRR and TRTC/ RCA. RCA stands for receive collision avoidance. The target is to increase the performance while reducing the processing overhead at each node. The performance of the TRTB and TRTC protocols are evaluated and compared in terms of queuing delay, burst loss rate, and channel utilization by OPNET simulation. The effects of various design parameters are also investigated through simulation in order to evaluate their scalability. In all the proposed schemes, tokens are just used to denote the accessibility of each wavelength. Finally, as an alternative, we also propose a new scheme based on the TRTC protocol called TRTC/CAT (collision avoidance by tokens) to avoid contention by using tokens.

A Study on Deflection Routing in Optical Burst-Switched Networks

A major concern in optical burst-switched networks is contention,which occurs when multiple bursts contend for the same link. While a deflection routing protocol is proposed as one of the contention resolution techniques,there has been no appropriate deflection routing algorithm to find an alternate route. In this paper, we formulate a deflection routing problem based on the burst blocking rate resulting from resource contention in an optical burst-switched network. This algorithm minimizes the contention on the alternate path with the minimum distance. Furthermore, in this paper, we develop an analytical model for the deflection routing time when deflection routing is performed to resolve contention. In this model, we investigate the expected deflection routing time considering that the burst could be dropped even with deflection routing due to another contention on the alternate path. Simulations are conducted to show that there is an improvement in terms of burst loss rate and network throughput.     

解决光突发交换竞争的新模型

针对光突发中的竞争问题，提出了一种分割反馈模型，相应地建立了数学分析模型，并进行了仿真与性能分析。结果表明这一模型是解决光突发交换中竞争问题的一个较佳方案。     

A review of routing strategies for optical burst switched networks

The exact contribution of this paper is a review of existing state‐of‐the‐art routing strategies for optical burst switched networks developed by researchers to deal with burst contention before it happens. Routing schemes are implemented in space domain, which make them simple and cost effective. Additionally, the paper points out the importance of routing as an effective way to deal with burst contention compared to other solutions. It also underlines the main differences between contention avoidance schemes and contention resolution techniques for optical burst switched networks. We believe that this review will help different optical burst switched researchers involved in the development of route optimization algorithms to control burst contention. Copyright © 2011 John Wiley & Sons, Ltd.     

A dynamic load-aware congestion control scheme in optical burst switching networks

The most important design goal in Optical Burst Switching (OBS) networks is to reduce burst loss resulting from resource contention. Especially, the higher the congestion degree in the network is, the higher the burst loss rate becomes. The burst loss performance can be improved by employing an appropriate congestion control. In this paper, to actively avoid contentions, we propose a dynamic load-aware congestion control scheme that operates based on the highest (called ‘peak load’) of the loads of all links over the path between each pair of ingress and egress nodes in an OBS network. We also propose an algorithm that dynamically determines a load threshold for adjusting burst sending rate, according to the traffic load in a network. Further, a simple signalling method is developed for our proposed congestion control scheme. The proposed scheme aims to (1) reduce the burst loss rate in OBS networks and (2) maintain reasonable throughput and fairness. Simulation results show that the proposed scheme reduces the burst loss rate significantly, compared to existing OBS protocols (with and without congestion control), while maintaining reasonable throughput and fairness. Simulation results also show that our scheme keeps signalling overhead due to congestion control at a low level.     

Hybrid offset‐time and burst assembly algorithm (H‐OTBA) for delay sensitive applications over optical burst switching networks

Optical burst switching (OBS) is the most favourable switching paradigm for future all‐optical networks. Burst assembly is the first process in OBS and it consists of aggregating clients packets into bursts. Assembled bursts wait for an offset time before being transmitted to their intended destinations. Offset time is used to allow burst control packet reserve required resources prior to burst arrival. Burst assembly process and offset‐time create extra delay in OBS networks. To make OBS suitable for real time applications, this extra latency needs to be controlled. This paper proposes and evaluates a novel offset time and burst assembly scheme to address this issue. Constant bit rate (CBR) traffic that has stringent end‐to‐end delay QoS requirements is used in this study. The proposed scheme is called hybrid offset‐time and burst assembly algorithm (H‐OTBA). The objective of the paper is achieved by controlling maximum burst transfer delay parameters of CBR. The proposed scheme was evaluated via network simulation. Simulation results demonstrate that, H‐OTBA has effectively reduced end‐to‐end delay for CBR traffic compared with current solutions. Copyright © 2014 John Wiley & Sons, Ltd.