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.     

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.     

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.     

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。     

Control architecture in optical burst-switched WDM networks

Optical burst switching (OBS) is a promising solution for building terabit optical routers and realizing IP over WDM. In this paper, we describe the basic concept of OBS and present a general architecture of optical core routers and electronic edge routers in the OBS network. The key design issues related to the OBS are also discussed, namely, burst assembly (burstification), channel scheduling, burst offset-time management, and some dimensioning rules. A nonperiodic time-interval burst assembly mechanism is described. A class of data channel scheduling algorithms with void filling is proposed for optical routers using a fiber delay line buffer. The LAUC-VF (latest available unused channel with void filling) channel scheduling algorithm is studied in detail. Initial results on the burst traffic characteristics and on the performance of optical routers in the OBS network with self-similar traffic as inputs are reported in the paper.     

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.     

The study of QoS guarantee in the optical burst switching internet backbone

Optical switching technology can be categorized into optical circuit switching (OCS), optical packet switching (OPS) and optical burst switching (OBS). OCS is suitable for large amounts of data transmission; however, the channel utilization is inefficient when the traffic flows are intermittent. OPS can be easily adapted to any higher layer and is suitable for bursty traffic, but it requires a highly complex technology and optical buffer. The new switching paradigm, OBS, can provide higher bandwidth utilization and meanwhile avoid the complexity in OPS technology.In this paper, we investigate how the quality of service (QoS) can be guaranteed and reliable transmission can be supported in the OBS-based Internet backbone. We propose the adjustable-time-counter-based (ATCB) burst assembly and the non-real time packet retransmission mechanisms and apply them in the ingress router of the OBS Internet backbone to guarantee the quality of real time applications and lossless requirement of non-real time services. Moreover, traffic shaped is performed for real time packets in the egress router so that the real time property is preserved with a low jitter. Simulation results show that the burst blocking probability using the ATCB burst assembly is improved, compared with the time-counter-based (TCB) and burst-length-threshold-based (BLTB) mechanisms. The delay, loss and jitter of real time service conform to the QoS requirement. Meanwhile, the delay of non-real time service also falls in the acceptable range.     

光突发交换网络的突发包组装和调度

光突发交换(OBS)由于结合了光线路交换和光分组交换的优点并且改进了两者的不足之处,成为实现IP over WDM的重要手段。主要研究实现光突发包在边缘路由器的组装生成和调度机制。通过模拟的方法研究边缘路由器的输出性能,包括输出流量的形状和时延特性。结果显示,不同服务等级的时延要求可以通过组装控制输出流的最大时延得以保证。同时边缘路由器组装和分配信道缓冲区设置和优先分配机制可以影响到输出光突发包的长度和突发度。     

A unified study of burst assembly in optical burst switching networks

This article presents a comprehensive study of burst assembly in optical burst switching (OBS) networks. This investigation aims to provide a unified study of burst assembly algorithms. After analyses of conventional assembly algorithms, we present an adaptive burst assembly algorithm: data-length time-lag product assembly algorithm. Numerical results show that the proposed algorithm takes the real-time traffic state into account to adapt burst length and its injected intervals. It obtains a more acceptable performance. Moreover, we investigated the impact of burst assembly applied at the edge of OBS networks. We analyze the Hurst parameter of the input traffic to the output traffic that results from the burst assembly. Two formulas are presented to describe changes of the Hurst parameter. Theoretical results are validated through extensive simulations in time-based, length-based, and adaptive assembly algorithms, respectively.     

Using multiple per egress burstifiers for enhanced TCP performance in OBS networks

Burst assembly mechanism is one of the fundamental factors that determine the performance of an optical burst switching (OBS) network. In this paper, we investigate the influence of the number of burstifiers on TCP performance for an OBS network. The goodput of TCP flows between an ingress node and an egress node traveling through an optical network is studied as the number of assembly buffers per destination varies. First, the burst-length independent losses resulting from the contention in the core OBS network using a non-void-filling burst scheduling algorithm, e.g., Horizon, are studied. Then, burst-length dependent losses arising as a result of void-filling scheduling algorithms, e.g., LAUC-VF, are studied for two different TCP flow models: FTP-type long-lived flows and variable size short-lived flows. Simulation results show that for both types of scheduling algorithms, both types of TCP flow models, and different TCP versions (Reno, Newreno and Sack), TCP goodput increases as the number of burst assemblers per egress node is increased for an OBS network employing timer-based assembly algorithm. The improvement from one burstifier to moderate number of burst assemblers is significant (15–50% depending on the burst loss probability, per-hop processing delay, and the TCP version), but the goodput difference between moderate number of buffers and per-flow aggregation is relatively small, implying that an OBS edge switch should use moderate number of assembly buffers per destination for enhanced TCP performance without substantially increasing the hardware complexity.

TCP Window-Based Flow-Oriented Dynamic Assembly Algorithm for OBS Networks

In transport control protocol (TCP) over optical burst switching (OBS) networks, TCP window size and OBS parameters, including assembly period and burst dropping probability, will impact the network performance. In this paper, a parameter window data dropping probability(WDDP), is defined to analyze the impact of the assembly and the burst loss on the network performance in terms of the round trip time and the throughput. To reduce the WDDP without introducing the extra assembly delay penalty, we propose a novel TCP window based flow-oriented assembly algorithm dynamic assembly period (DAP). In the traditional OBS assembly algorithms, the packets with the same destination and class of service (CoS) are assembled into the same burst, i.e., the packets from different sources will be assembled into one burst. In that case, one burst loss will influence multiple TCP sources. In DAP, the packets from one TCP connection are assembled into bursts, which can avoid the above situation. Through comparing the two consecutive burst lengths, DAP can track the variation of TCP window dynamically and update the assembly period for the next assembly. In addition, the ingress node architecture for the flow-oriented assembly is designed. The performance of DAP is evaluated and compared with that of fixed assembly period (FAP) over a single TCP connection and multiple TCP connections. The results show that DAP performs better than FAP at almost the whole range of burst dropping probability.     

Edge node buffer usage in optical burst switching networks

Optical Burst Switching (OBS) combines the benefits of Optical Packet Switching and Optical Circuit Switching technologies to provide an efficient, yet cost effective, method for data transmission in an all-optical, bufferless, core network. While most studies on OBS has concentrated on the core OBS network, we contribute new studies for the buffer requirement of an OBS edge node. The buffer usage for OBS systems only arises in the edge nodes since they contain an array of assemblers which combines electronic data with a common destination into an OBS burst stream for transmission in an all-optical bufferless core network. Specifically, we present two analytical results for buffer usage in an OBS edge node: one for Poisson traffic and the other for self-similar traffic input. The results show that the aggregated traffic from many assemblers inherits the characteristics of the source input traffic. This means that the output traffic approaches Poisson if the input traffic is Poisson, and the output traffic remains self-similar if the input is self-similar. These results lead to the following important design issues when dimensioning buffer requirements in an OBS edge node: if the traffic input is Poisson, the M/G/m model is the model to use for obtaining the upper bound on buffer usage in an OBS edge node; and for the case of self-similar traffic, Brichet’s method can be used to provide the upper and lower bound.     

Burstification Queue Management in Optical Burst Switching Networks

Among the various issues lying in optical burst switching (OBS) networks, burstification, i.e., assembling multiple IP packets into bursts, is an important one. Between the two important aspects related to burst assembly, the burst assembly algorithm aspect has been extensively studied in the literature. However, as far as we know, there is no research about the burstification queue management (BQM) aspect, which refers to how many burstification queues (BQ) we should set at each OBS edge node and how to manage these BQs. Suppose there are G destinations (egress edge nodes) and the OBS network provides S different quality of service (QoS) classes. Traditionally, it is simply regarded that each ingress edge node needs G· S queues to sort incoming packets, one for each possible destination and QoS class. For simplicity, we call this policy the static dedicate BQM (SDB) policy. The SDB policy, though simple, lacks scalability since we have to add S BQs at each OBS edge node if an extra OBS edge node is added to the OBS network. To solve this problem, we propose in this paper two BQM policies: quasi-static BQM (QSB) policy and dynamic BQM (DB) policy. For the QSB policy, we derive the packet loss probability due to lacking BQs based on a Markov chain, from which we can work out the employed number of BQs for a given packet loss probability. Based on these results, the scalability of the QSB policy is also studied. With the DB policy, we not only can dynamically assign BQs for incoming packets, but also can dynamically allocate buffer capacity for each BQ by using a least-mean-square (LMS)-based linear prediction filter. The performance of the DB policy is investigated by analysis and extensive simulations. We also compared the performance of the QSB policy and the DB policy. Results from analysis and simulation demonstrate that the DB policy is the best.     

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.

Modeling and Synthesis of Traffic in Optical Burst-Switched Networks

We analyze burst assembly process as the main building block of the optical burst switching (OBS) paradigm. The analysis is performed for time-based, volume-based, as well as hybrid burst assemblers. Under the assumption that the process of packet arrival to the assembly buffer is Poisson, exact analytical expressions are derived for length and interdeparture time of bursts that are generated by these three classes of assembly algorithms. Furthermore, we consider the issue of generating burst trace, which arises during the performance evaluation of OBS networks through discrete-event simulation. In such a simulation study, a significant part of the simulation time, particularly in the case of a network with a large number of ingress nodes, is used by the implementation of the burst assembly algorithms. This is due to the fact that each data burst is a result of aggregating several short-length packets, which-in a straightforward approach-have to be individually generated and, afterward, ldquomeltedrdquo into the burst. We present a novel approach to fast generation of bursts, which is based on the analytical models that are developed for burst length and burst interdeparture time distributions as well as an efficient generation technique (composition) supporting the generation of these distributions. The analysis is completed by numerical results that validate the accuracy of developed models and demonstrate the speedup gain of using proposed burst generation algorithms.     

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.     

基于ON/OFF源模型的OBS汇聚算法研究

近年来,大量研究表明,网络业务流量呈现长相关、自相似的特性,采用ON/OFF源模型生成自相似流能够比较真实地反映现实网络中的业务流量。光突发包的汇聚算法是光突发交换的关键技术之一,利用ON/OFF模型生成的自相似流对几种典型的OBS汇聚算法进行研究。仿真表明,不同算法对自相似的影响不同。     

On the blocking time distribution of core OBS switches

Given the bufferless nature of Optical Burst- Switched networks, data bursts are either transmitted or dropped; the latter typically occurs when all the wavelengths of a given output port are occupied. Clearly, the amount of time during which a given output port is blocked and cannot schedule incoming data bursts is a key performance measure of OBS networks. This work shows that, under Poissonian burst arrivals, the blocking time distribution of a given output port in an OBS node approaches the exponential distribution as the number of wavelengths increases. It is further shown that this behavior remains regardless of the size distribution of incoming bursts, and therefore, regardless of the burst-assembly algorithms employed at the border nodes. Finally, this result is also applied to the characterization of the amount of overspill traffic, that is, the number of bursts that arrive within a blocked period, and therefore must be either dropped or diverted over alternative routes.