A novel optical burst switching scheme—logical cascaded private subnet with start wavelength assignment policy

Many recent studies have convincingly demonstrated that network traffic exhibits a noticeable self-similar nature, which has a considerable impact on network performance, and most studies of optical burst switching (OBS) networks are under a fundamental assumption that full wavelength conversion is available throughout the network. In practice, however, economic and technical considerations are likely to dictate a more limited and sparse deployment of wavelength converters in the optical network. Therefore, we present a novel scheme for OBS networks, called logical cascaded private subnet (LCPN) with start wavelength assignment policy. We define the concept of canoe relative to cluster in self-similar traffic, and introduce a new device named payload segregator at the edge node as a gateway to the core node in OBS Networks. According to the changes in the edge node framework, we put forward the concept of cluster private subnet and canoe private subnet in the core node correspondingly. A new start wavelength assignment policy is proposed for the absence of (full) wavelength conversion capabilities in the core node of OBS Networks. The performance study indicates that, our new scheme is robust under self-similar traffic and wavelength continuity constraint.     

波长变换对光突发交换网络性能的影响

介绍了光突发交换原理及波长变换技术.模拟了基于美国国家科学基金网络模型的光突发交换.数据源选用具有自相似性的突发性数据源,采用JET(Just-enough-time)信令协议,使用LAUC-VF数据信道调度算法.为减小竞争的发生,在网络中加入波长变换器.对带波长变换器和不带波长变换器的网络的性能进行了模拟,并对结果进行了分析.     

Analysis of a dynamically wavelength-routed optical burst switchednetwork architecture

The concept of optical burst switching (OBS) aims to allow access to optical bandwidth in dense wavelength division multiplexed (DWDM) networks at fractions of the optical line rate to improve bandwidth utilization efficiency. This paper studies an alternative network architecture combining OBS with dynamic wavelength allocation under fast circuit switching to provide a scalable optical architecture with a guaranteed QoS in the presence of dynamic and bursty traffic loads. In the proposed architecture, all processing and buffering are concentrated at the network edge and bursts are routed over an optical transport core using dynamic wavelength assignment. It is assumed that there are no buffers or wavelength conversion in core nodes and that fast tuneable laser sources are used in the edge routers. This eliminates the forwarding bottleneck of electronic routers in DWDM networks for terabit-per-second throughput and guarantees forwarding with predefined delay at the edge and latency due only to propagation time in the core. The edge burst aggregation mechanisms are evaluated for a range of traffic statistics to identify their impact on the allowable burst lengths, required buffer size and achievable edge delays. Bandwidth utilization and wavelength reuse are introduced as new parameters characterizing the network performance in the case of dynamic wavelength allocation. Based on an analytical model, upper bounds for these parameters are derived to quantify the advantages of wavelength channel reuse, including the influence of the signaling round-trip time required for lightpath reservation. The results allow to quantify the operational gain achievable with fast wavelength switching compared to quasistatic wavelength-routed optical networks and can be applied to the design of future optical network architectures     

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。     

光突发交换网络中新型减小竞争冲突方案

光突发交换是下一代光网络中的有效核心交换技术之一,在光突发交换网络中数据突发的调度是影响交换性能的重要因素,如何有效地对数据突发进行合理调度,以减小丢包率正是关键问题所在.采用在波长域业务整形与边缘节点延迟调度相结合的方法对数据突发进行调度,与LAUC-VF算法进行仿真对比分析,该方法能有效地降低突发包丢失率.     

Analysis of OBS Networks With Limited Wavelength Conversion

Presented herein is a scalable framework for estimating path blocking probabilities in optical burst switched (OBS) networks where limited wavelength conversion is possible. Although presented under the guise of OBS, it is pertinent to a broader class of optical networks based on the principle of bufferless unacknowledged switching. By applying the framework to the NSFNET topology, it is shown that even the most limited conversion range may reduce path blocking probabilities by several orders of magnitude, compared with no wavelength conversion. Moreover, contrary to previous results derived for all-optical non-OBS networks with acknowledgement, OBS with full wavelength conversion achieves significantly lower blocking probabilities than OBS with limited wavelength conversion when the conversion range is small. Underpinning the framework is a generalization of the classical reduced load approximation. Assuming links evolve independently of each other allows decoupling of the network into its constituent links. A set of fixed-point equations describing the evolution of each conversion range are then solved by successive substitution to estimate link blocking probabilities. Having these link blocking probabilities, path blocking probabilities are evaluated. The complexity of the framework is dominated by the wavelength conversion range and is independent of the number of wavelengths per link under certain symmetry conditions. Both just-in-time (JIT) and just-enough-time (JET) scheduling are considered. Simulations are implemented to corroborate the accuracy of the framework.     

Priority-based offline wavelength assignment in OBS networks

Optical burst switching (OBS) is a promising technique for wavelength division multiplexing (WDM) networks. In practice, wavelength converters (WCs) are either absent or only sparsely deployed in WDM networks due to economic and technical limitations. Thus, wavelength assignment is expected to be an important component of OBS networks. In this paper, an offline wavelength assignment scheme in OBS networks without wavelength conversion capability is proposed. The key idea of the scheme is to decide the wavelength searching order of each traffic connection at edge nodes according to the wavelength priorities determined by the calculated burst loss probabilities on different wavelengths. Simulation results indicate that the proposed scheme can reduce the network-wide burst loss probability significantly compared with other schemes. It is also illustrated that the performance of the proposed scheme can be further enhanced by a larger number of wavelengths per link and a reasonable delay bound at edge nodes.     

A Data Burst Assembly Algorithm in Optical Burst Switching Networks

Presently, optical burst switching (OBS) technology is under study as a promising solution for the backbone of the optical Internet in the near future because OBS eliminates the optical buffer problem at the switching node with the help of no optical/electro/optical conversion and guarantees class of service without any buffering. To implement the OBS network, there are a lot of challenging issues to be solved. The edge router, burst offset time management, and burst assembly mechanism are critical issues. In addition, the core router needs data burst and control header packet scheduling, a protection and restoration mechanism, and a contention resolution scheme. In this paper, we focus on the burst assembly mechanism. We present a novel data burst generation algorithm that uses hysteresis characteristics in the queueing model for the ingress edge node in optical burst switching networks. Simulation with Poisson and self‐similar traffic models shows that this algorithm adaptively changes the data burst size according to the offered load and offers high average data burst utilization with a lower timer operation. It also reduces the possibility of a continuous blocking problem in the bandwidth reservation request, limits the maximum queueing delay, and minimizes the required burst size by lifting up data burst utilization for bursty input IP traffic.     

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.     

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.     

Analysis of blocking probability in optical burst switched networks

In this article, we study the blocking probability in a wavelength division multiplexing (WDM) based asynchronous bufferless optical burst switched (OBS) network, equipped with a bank of wavelength converters. Our analysis encloses two wavelength reservation schemes JIT (just-in-time) and JET (just-enough-time), and two-class data rate. The contribution of our work includes: (i) derivation of an accurate model for blocking probability of lower priority bursts in case of a non-preempted model; (ii) provision of the analytical model for blocking probability calculation in the OBS network, which includes these variables: two signaling schemes, partial wavelength conversion, two-class data, traffic intensity, cross-connect speed, number of wavelengths in WDM fiber, number of fibers in the node, number of wavelength converters, and number of nodes in the path; (iii) simulation results, which show that partial wavelength conversion provide quite satisfactory quality of service. We compare performance in a single OBS node, under various sets of parameter values. The OBS network shows great flexibility in terms of used multiclass data, and there is no dependence on the used higher layer protocol.     

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.     

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.     

Congestion-Controlled Optical Burst Switching Network With Connection Guarantee: Design and Demonstration

A congestion-controlled optical burst switching network that offers connection guarantees was designed to handle bursts as short as 100 ms with switching within 10 ms in networks less than 200 km long. Its optical burst switching (OBS) is based on circuit switching, and transport is by optical burst paths. Five metrics are proposed for evaluating OBS network performance. The application area to be laid and the data application were determined in accordance with the design target. Given a reasonable burst block probability requirement, design criteria are developed on the basis of wavelength switching and conversion implementation. OBS network performance is tested in field trials on the Japan Gigabit Network II testbed. Fast congestion control through the use of precalculated detour routes is demonstrated.      

LOBS技术研究

光突发交换技术(OBS)是一种新出现的光交换技术,它综合了光波长路由和光分组交换的优点。本文的LOBS又将MPLS 和OBS这两大技术结合在一起,利用MPLS强大的控制能力为OBS网络在QoS、流量工程和网络恢复等方面提供良好的支持。文章根据LOBS的基本原理,提出并详细阐述了它的网络构成和工作机制,最后指出了LOBS网络在流量工程和网络生存性方面相对其他光网络的优越性。     

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 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.     

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.     

Contention resolution and QoS provisioning using sparse fiber delay lines in WDM networks

In this paper, we combine fiber delay lines (FDL) and optical wavelength conversion (OWC) as the solution for the burst contention problem in optical burst switching (OBS). We present a placement algorithm, k-WDS, for the sparse placement of FDLs at a set of selected nodes in the network. The algorithm can handle both uniform and non-uniform traffic patterns. Our extensive performance tests show that k-WDS provides more efficient placement of optical fiber delay lines than the well-known approach of placing the resources at nodes with the highest experienced burst loss. Performance results are also given to compare the benefit of using FDLs alone, OWCs alone, as well as a mixture of both FDLs and OWCs. A new algorithm, A-WDS, for the placement of an arbitrary numbers of FDLs and OWCs is presented and evaluated under different uniform and non-uniform traffic loads using network simulation of the NSFNET topology and randomly generated graphs. The paper is concluded by presenting the design of a cost-effective optical switch equipped with variable-delay FDL bank. Based on the switch design, a scheme to provide differentiated services for multiple classes of traffic is presented and evaluated.