Dynamic wavelength selection and delayed burst assignment schemes for Optical Burst Switching networks

Optical Burst Switching (OBS) has been proposed as a promising switching technology for the next generation of optical transport networks. In this paper, we address the issue of how to provide proportional differentiated services in OBS networks. Firstly, a Dynamic Wavelength Selection (DWS) scheme is introduced to provide proportional differentiated services in bufferless OBS networks by dynamically assigning more and longer periods of wavelengths to high priority classes. This scheme can also utilize wavelengths efficiently because the wavelengths are shared among different classes. Next, a Delayed Burst Assignment (DBA) scheme is introduced, by which bursts of the high priority class are given a higher probability for reserving wavelengths by scheduling the bursts of the low priority class with a delay to provide quality of service (QoS) in OBS networks. The integration of these two schemes provides proportional differentiated services and improves the burst loss performance by giving the burst head packet (BHP) two opportunities of scheduling its data burst (DB).     

New assembly techniques and fast reservation protocols for optical burst switched networks based on traffic prediction

We propose new burst assembly schemes and fast reservation (FR) protocols for Optical Burst Switched (OBS) networks that are based on traffic prediction. The burst assembly schemes aim at minimizing (for a given burst size) the average delay of the packets incurred during the burst assembly process, while the fast reservation protocols aim at further reducing the end-to-end delay of the data bursts. The burst assembly techniques use a linear prediction filter to estimate the number of packet arrivals at the ingress node in the following interval, and launch a new burst into the network when a certain criterion, different for each proposed scheme, is met. The fast reservation protocols use prediction filters to estimate the expected length of the burst and the time needed for the burst assembly process to complete. A Burst Header Packet (BHP) packet carrying these estimates is sent before the burst is completed, in order to reserve bandwidth at intermediate nodes for the time interval the burst is expected to pass from these nodes. Reducing the packet aggregation delay and the time required to perform the reservations, reduces the total time needed for a packet to be transported over an OBS network and is especially important for real-time applications. We evaluate the performance of the proposed burst assembly schemes and show that a number of them outperform the previously proposed timer-based, length-based and average delay-based burst assembly schemes. We also look at the performance of the fast reservation (FR) protocols in terms of the probability of successfully establishing the reservations required to transport the burst.     

Burst scheduling for differentiated services in optical burst switching WDM networks

Optical burst switching (OBS) is one of the most important switching technologies for future optical wavelength division multiplexing (WDM) networks and the Internet. The model of differentiated services has been proposed to support quality of service (QoS) in the IP‐based Internet. It is also very important to have differentiated service support in OBS networks. When the burst scheduling in an OBS network is set up appropriately, network can support differentiated services. In this paper, we proposed a new burst scheduling scheme, called differentiated scheduling with identical priority offset time (DSIPO). In DSIPO, the same priority offset time is used for all the bursts destined to the same edge node regardless of their priorities. Differentiated services in terms of burst loss probability are achieved by processing the control packets of higher priority class bursts, thus reserving resources for their data bursts, more promptly upon their arrival than those of lower priority class bursts. Each intermediate (core) node can adjust the burst loss probabilities of various burst classes by choosing its own differentiated processing delay value for each priority class or its own differentiated processing delay difference value between any pair of adjacent priority classes. We model and analyse DSIPO in terms of the burst loss probability for each priority class with simulation validation. The performance of DISPO is evaluated by simulation. Copyright © 2004 John Wiley & Sons, Ltd.     

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.     

An introduction to optical burst switching

Optical burst switching is a promising solution for all-optical WDM networks. It combines the benefits of optical packet switching and wavelength routing while taking into account the limitations of the current all-optical technology. In OBS, the user data is collected at the edge of the network, sorted based on a destination address, and grouped into variable sized bursts. Prior to transmitting a burst, a control packet is created and immediately sent toward the destination in order to set up a bufferless optical path for its corresponding burst. After an offset delay time, the data burst itself is transmitted without waiting for a positive acknowledgment from the destination node. The OBS framework has been widely studied in the past few years because it achieves high traffic throughput and high resource utilization. However, despite the OBS trademarks such as dynamic connection setup or strong separation between data and control, there are many differences in the published OBS architectures. In this article we summarize in a systematic way the main OBS design parameters and the solutions that have been proposed in the open literature.     

光突发交换中的突发包组装技术研究

光突发交换是近几年出现的一种很有前途的光交换技术，比电路交换灵活，带宽利用率高，又比光分组交换易于实现，突发包的组装是光突发交换的关键技术，在很大程度上影响到光突发交换网络的性能。文中介绍了光突发包的格式，描述了交换网络中突发包组装所需的层次结构和功能结构，并给出了一种典型的生成算法。最后，对选择突发包组装时间应考虑的各种因素进行了系统的分析。     

On blocking time in multi‐class optical burst switching nodes

Recently, there has been an increasing research interest being directed to optical burst switching (OBS) networks because of its mature electronic processing capability and high‐capacity optical transport capability. The blocking time for an OBS node, representing the time duration in which a certain channel is occupied by some class of bursts, plays an important role in characterizing the performance of an OBS network. In this paper, we analyze this important metric for an OBS node with a horizonal and a single channel theoretically and numerically. On the basis of that, the burst arrivals are assumed to follow the Poisson process and the burst lengths have a phase‐type distribution, we are able to formulate a working mechanism of an OBS node into a multilayer stochastic fluid model. Using a level crossing arguments method, we are able to obtain the Laplace–Stieltjes transforms of the blocking time, from which n ‐order moments and the probability density functions of the blocking time can be further derived. We provide a numerical example to illustrate the theoretical analyses, and we further discuss the effects of the offset time and the arrival density on the blocking time through this numerical example. Copyright © 2016 John Wiley & Sons, Ltd.     

Hybrid switching and p-routing for optical burst switching networks

One promising switching technology for wavelength-division multiplexing optical networks is optical burst switching (OBS). However, there are major deficiencies of OBS. (1) The delay offset between a control message and its corresponding data burst is based on the diameter of a network. This affects network efficiency, quality-of-service, and network scalability.( 2) OBS adopts one-way resource reservation scheme, which causes frequent burst collision and, thus, burst loss. We address the above two important issues in OBS. In particular, we study how to improve the performance of delay and loss in OBS. To reduce the end-to-end delay, we propose a hybrid switching scheme. The hybrid switching is a combination of lightpath switching and OBS switching. A virtual topology design algorithm based on simulated annealing to minimize the longest shortest path through the virtual topology is presented. To minimize burst collision and loss, we propose a new routing algorithm, namely, p-routing, for OBS network. The p-routing is based on the wavelength available probability. A path that has higher available probability is less likely to drop bursts due to collision. The probability-based p-routing can reduce the volatility, randomness, and uncertainty of one-way resource reservation. Our studies show that hybrid switching and p-routing are complementary and both can dramatically improve the performance of OBS networks.     

Performance evaluation of throughput in optical burst switching

Optical burst switching (OBS) provides a promising solution to utilize the huge terahertz bandwidth of optical wavelength division multiplexing (WDM) transmission technology. To exploit this bandwidth, several reservation schemes have been proposed that include just‐in‐time (JIT) signaling, just‐enough‐time (JET) signaling and burst segmentation (BS). It is necessary to investigate the performance of these schemes under the same constraints for a prescribed OBS application. Accordingly, in this paper, we analyzed and compared the performance of JIT, JET and BS techniques under various scenarios such as network size, delay variation and load variation in an OBS network using various performance metrics, such as the offset time and switch configuration time. Also, the performance of the network under various switching delays was also investigated. The modified BS reservation scheme has been found to yield significantly better performance and better throughput compared with the JIT and JET reservation schemes. Test results show that the effect of varying loads as well as delays significantly impacts the performance of the OBS network. The results presented in this paper are expected to lead further performance improvements in OBS networks using the BS reservation scheme. Copyright © 2010 John Wiley & Sons, Ltd.     

Contention resolution considering multicast traffic in optically burst-switched WDM networks

This paper proposes a contention resolution scheme considering multicast traffic in optical burst switching (OBS) networks. In OBS networks, for unicast bursts, contention can be avoided by deflection routing. However, deflection routing cannot be applied to multicast bursts because multicast bursts are transmitted along light-trees which are fixed, tree-shaped routes. Therefore, the loss probability of multicast bursts is generally high. To resolve this problem, the proposed scheme introduces an ingenious offset time assignment strategy which completely avoids contention of multicast bursts due to transmissions of unicast bursts by strategically assigning additional offset times. Furthermore, in the proposed scheme, unicast bursts avoid contention with deflection routing. Through simulation experiments, we show that the proposed scheme improves the loss probabilities of both of unicast bursts and multicast bursts.     

Optical burst switching: a viable solution for terabit IP backbone

Wavelength-division multiplexing has emerged as an important physical layer technology. Optical transmission provides a physical layer capable of carrying bits at the speed at the order of a gigabit per second. Optical burst switching is proposed to overcome the shortcomings of conventional WDM deployment, such as lack of fine bandwidth granularity in wavelength routing and electronic speed bottlenecks in SONET/SDH. We describe an architecture for IP network over the OBS WDM transmission core. The use of MPLS-type technique for forwarding data bursts and the inclusion of a medium access control layer between the optical (WDM) and IP layers are the key ingredients of the proposed architecture. In particular, the architecture is based on provisioning MPLS paths, also called label switched paths, of desired quality of service through the OBS WDM transmission core. The MAC layer performs various OBS-specific functions, such as burst assembly, burst scheduling, and offset setting/traffic shaping. While burst assembly and burst scheduling are relatively straightforward, we point out that the offset setting strategy has significant impact on the performance of IP network operating over OBS WDM core. We describe a shaping scheme to set the offset, an important system parameter for OBS, between the successive data bursts of a given data stream (label switched path) and their associated control packets. This scheme results in robust operation of the network and also facilitates traffic engineering. Guidelines are provided for implementing various IP QoS mechanisms in the optical backbone using OBS.     

A burst segmentation-deflection routing contention resolution mechanism in OBS networks

One of the key problems to hinder the realization of optical burst switching(OBS) technology in the core networks is the losses due to the contention among the bursts at the core nodes.Burst segmentation is an effective contention resolution technique used to reduce the number of packets lost due to the burst losses.In our work,a burst segmentation-deflection routing contention resolution mechanism in OBS networks is proposed.When the contention occurs,the bursts are segmented according to the lowest packet loss probability of networks firstly,and then the segmented burst is deflected on the optimum routing.An analytical model is proposed to evaluate the contention resolution mechanism.Simulation results show that high-priority bursts have significantly lower packet loss probability and transmission delay than the low-priority.And the performance of the burst lengths,in which the number of segments per burst distributes geometrically,is more effective than that of the deterministically distributed burst lengths.     

Traffic statistics and performance evaluation in optical burst switched networks

Optical burst switching (OBS) is a promising switching technology to exploit the potential benefits of optical communication and, at the same time, support statistical multiplexing of data traffic at a fine granularity. To quantify its benefits, the paper describes several typical burst assembly algorithms and studies their impact on the assembled burst traffic characteristics as well as the performance of TCP traffic. Also described is a proactive burst scheduling algorithm, called burst overlap reduction algorithm (BORA), which schedules locally assembled bursts in such a way as to reduce burst contention at downstream nodes in OBS networks. Furthermore, to provide analytical insights into performance evaluation of OBS networks, a burst loss model at an OBS node and its extension to different reservation protocols are presented.     

A non-competing hybrid optical burst switch architecture for QoS differentiation

In this paper, we present a new hybrid optical burst switch architecture (HOBS) that takes advantage of the pre-transmission idle time during lightpath establishment. In dynamic circuit switching (wavelength routing) networks, capacity is immediately hard-reserved upon the arrival of a setup message at a node, but it is used at least a round-trip time delay later. This waste of resources is significant in optical multi-gigabit networks and can be used to transmit traffic of a lower class of service in a non-competing way. The proposed hybrid OBS architecture, takes advantage of this idle time to transmit one-way optical bursts of a lower class of service, while high priority data explicitly requests and establishes end-to-end lightpaths. In the proposed scheme, the two control planes (two-way and one-way OBS reservation) are merged, in the sense that each SETUP message, used for the two-way lightpath establishment, is associated with one-way burst transmission and therefore it is modified to carry routing and overhead information for the one-way traffic as well. In this paper, we present the main architectural features of the proposed hybrid scheme and further we assess its performance by conducting simulation experiments on the NSF net backbone topology. The extensive network study revealed that the proposed hybrid architecture can achieve and sustain an adequate burst transmission rate with a finite worst case delay.     

OBS网络中基于优先级的先分割后缓存冲突解决方法

为了有效地降低突发包的丢失率和保证OBS网络中不同优先级业务的服务质量,提出了一种基于优先级的先分割后缓存冲突解决方法。该方法通过在多波长信道系统的输出数据信道上设置光纤延迟线组来缓存被分割的冲突突发包。当冲突发生时,首先基于突发包的优先级和处理完毕时间进行"竞争突发包头部分割或者原突发包尾部分割"处理;无冲突部分进行交换或者直接在事先预留的输出数据信道上处理,冲突部分的分割突发包进行光缓存。仿真结果表明,多波长信道系统中,高优先级突发包的丢失率低于低优先级突发包的丢失率。同时该方法在一定程度上可以有效地减少端到端的传输时延和整个网络的丢包率,从而提高整个OBS网络的性能。     

OBS网络中一种新型的避免冲突方法

突发包冲突在无光缓存能力的光突发交换(OBS)网络中是一个尚未解决的问题.在对JET协议进行改进的基础上,文章首次提出了一种新型的突发包冲突解决方案,分析了其可行性及相对传统算法的优势.     

An adaptive load-aware burst assembly scheme to achieve optimal performance of FDL buffers in OBS networks

Optical burst switching (OBS) is regarded as one of the most promising switching technologies for next generation optical networks. Contention resolution of data bursts is a critical mission to implement practical OBS. The use of fiber delay line (FDL) buffers has received a lot of attention as a fundamental but effective solution to resolve burst contention. Several studies have investigated the way to achieve the optimal performance of FDL buffers at a single-node level. However, this article studies how to achieve the best performance of OBS networks with FDL buffers under varying traffic condition at a network level. For this purpose, we propose an adaptive load-aware burst assembly (ALBA) scheme, which adaptively adjusts the size threshold of burst assembler optimized to the current network traffic load. A piggybacking method used to deliver the traffic-load information from core nodes to ingress edge nodes accelerates the adaptiveness of the proposed scheme by reducing the update time of the size threshold. The effectiveness of the ALBA scheme is proved by comparing with No-FDL case and fixed size-threshold cases under changing traffic-load environment from extensive simulation tests.

定长光突发交换节点的QoS性能分析

分析了光突发交换网络中基于附加偏移时间(EOT,extra offset time)的业务优先等级区分服务的变长突发方案的不足，提出了一种定长光突发方案。它能在较小附加延迟的情况下保证高优先级的业务完全不受低优先级业务的阻塞，即使每个优先级的附加等待时间都减小到变长突发方案的1/3，同时使最高优先级业务的阻塞率更小，而且具有现实可行性。     

A distributed backoff-channel deflection algorithm with load balancing for optical burst switching networks

Optical burst contention is one of the major factors that cause the burst loss in the optical burst switching (OBS) networks. So far, various contention resolution schemes have been proposed. Among them, the deflection path is more attractive due to its low requirement for optical buffer in capability and quantity. However, these deflection path algorithms do not consider the successful transmission rate of deflection traffic, and the deflection traffic??s impacts on the original traffic of the deflection path are not concerned. Meanwhile, the offset-time deficit problem for deflected bursts is ignored. Therefore, in order to reduce the burst loss probability in OBS networks, a Distributed Backoff-channel DeFlection algorithm with load balancing, for short DBDF-LB, is proposed. It consists of two parts, that is, the deflection with load balancing and the backoff-channel buffering scheme. Firstly, from the perspective of the network-wide load balancing, the optimal deflection path, on which the contention-failure burst is deflected with the minimum hops and the least burst loss probability, is selected. Secondly, the extra offset-time for the deflected burst is provided through the backoff-channel scheme. Finally, by numerical simulations, compared with the classical shortest path deflection algorithm, the DBDF-LB can obviously reduce the burst loss probability, about 50%, with a little extra overhead.     

Dynamic threshold-based assembly algorithms for optical burst switching networks subject to burst rate constraints

Control plane load stems from burst control packets which need to be transmitted end-to-end over the control channel and further processed at core nodes of an optical burst switching (OBS) network for reserving resources in advance for an upcoming burst. Burst assembly algorithms are generally designed without taking into consideration the control plane load they lead to. In this study, we propose traffic-adaptive burst assembly algorithms that attempt to minimize the average burst assembly delay subject to burst rate constraints and hence limit the control plane load. The algorithms we propose are simple to implement and we show using synthetic and real traffic traces that they perform substantially better than the usual timer-based schemes.