Provision of differentiated performance in Optical Burst Switching networks based on burst assembly processes

Optical Burst Switching (OBS) has been designed as a practical solution for the high-speed transport network using enabling optical technologies, which can work without optical buffering or pure optical signal processing in the intermediate nodes. As a collection of many packets, optical bursts exhibit different traffic characteristics in the bufferless optical core networks compared to the packet-level traffic in the conventional electronic switching systems. However, many OBS studies often neglect this issue by assuming the inputs to be optical bursts when analyzing the system performance. This paper demonstrates that the loss performance of optical bursts is dramatically different when considering burst assembly process at the edge nodes and the connectivity of the core nodes. We develop some analytical models which can model the loss performance more accurately than the traditional methods. Based on our observations, we propose a scheme to support differentiated loss performances for optical bursts by modifying the burst assembly parameters at the source edge nodes. Our scheme is implemented at the edge nodes and there is no specific requirement to the core nodes. Thus, our design provides good flexibility and scalability in the heterogeneous Internet.     

On burst rescheduling in OBS networks with partial wavelength conversion capability

The core nodes in an optical burst switching (OBS) network are normally equipped with wavelength converters (WCs) to reduce the burst loss probability. Since WCs are expensive and still immature technologically, it is desirable to reduce the number of WCs in the network and to have partial wavelength conversion capability at the core nodes. Nevertheless, a majority of algorithms in the literature are proposed under the full wavelength conversion assumption. As a result, they do not consider the burst loss caused by insufficient WCs, i.e., bursts dropped due to the unavailability of free WCs to convert them to unused wavelengths. In this paper, we demonstrate how to use burst rescheduling to decrease the burst loss due to insufficient WCs and hence cut down on the overall burst loss probability in OBS networks. Two burst rescheduling algorithms are proposed. Their effectiveness in reducing the overall burst loss probability is verified through simulation experiments.     

OBS网络中基于优先级与概率的偏射路由算法*

摘 要：为了保证OBS网络中不同优先级业务的服务质量和解决偏射算法在偏射控制上的问题,提出了一种基于优先级与概率的偏射路由算法。该算法根据突发包的优先级和转发概率来控制突发包的偏射,并从网络突发阻塞概率的意义上寻找最佳偏射路由。当冲突发生时,分割优先级低的突发包,并将分割突发包偏射到空闲的链路上;节点根据链路上指定的权值,按概率为分割突发包选择一条可以使网络突发阻塞概率最小的最佳偏射路由。仿真结果表明,虽然网络中可选路由数目的增加对网络性能的改善非常有限,但是该算法能够有效的降低整个网络的丢包率,并且得到的高优先级突发包的丢失率低于低优先级突发包的丢失率,从而很好的保障了网络的服务质量。故这种方法能够有效的提高OBS网络的性能。     

On ordered scheduling for optical burst switching

Optical burst switching (OBS) is a promising optical networking paradigm for efficient transport of bursty IP traffic over wavelength division multiplexing (WDM) optical Internet networks. In OBS, the header of a burst is sent in advance of the data burst to reserve a wavelength channel at each optical switching node along the path. The nodes use a scheduling algorithm to assign wavelengths to incoming bursts. Our work is motivated from the observation that existing scheduling algorithms assign a wavelength to a burst when its header arrives at the node. Thus, information about other bursts whose headers arrive later is not available when the scheduling decision is made. This leads to suboptimal scheduling decisions and unnecessary burst dropping. The key idea in our proposed algorithm, Ordered Scheduling, is to defer making the scheduling decision until just before the burst arrival in order to have full knowledge about other bursts. The effectiveness of the proposed algorithm is studied through simulation and the computational complexity and signalling overhead are analysed.     

An integrated congestion control mechanism for optimized performance using two-step rate controller in optical burst switching networks

Optical burst switching (OBS) is a promising solution to implement the optical internet backbone. However, the lack of adequate congestion-control mechanisms may result in high burst loss. Schemes such as fiber delay line (FDL), wavelength conversion, and deflection routing to reduce burst collision are unable to prevent the network congestion effectively. To address this problem, we propose and investigate a global solution, called Integrated Congestion-Control Mechanism (ICCM), for OBS networks. ICCM, which combines congestion avoidance with recovery mechanism, restricts the amount of burst flows entering the network according to the feedback information from core routers to edge routers to prevent network congestion. Also, a flow-policing scheme is proposed to intentionally drop the overloaded traffic with a certain probability at a core router to support fairness among flows. Moreover, the transmission rate of each flow is controlled to achieve optimized performance such as maximizing throughput or minimizing loss probability using two-step rate controller at the edge router. Simulation results show that ICCM effectively eliminates congestion within the network and that, when combined with a flow-policing mechanism, the fairness for competing flows can be supported while maintaining effective network performance.     

An optical burst reordering model for time-based and random selection assembly strategies

Contention resolution schemes in optical burst switched networks (OBS) as well as contention avoidance schemes delay burst delivery and change the burst arrival sequence. The burst arrival sequence usually changes the packet arrival sequence and degrades the upper layer protocols performance, e.g., the throughput of the transmission control protocol (TCP).In this paper, we present and analyze a detailed burst reordering model for two widely applied burst assembly strategies: time-based and random selection. We apply the IETF reordering metrics and calculate explicitly three reordering metrics: the reordering ratio, the reordering extent metric and the TCP relevant metric. These metrics allow estimating the degree of reordering in a certain network scenario. They estimate the buffer space at the destination to resolve reordering and quantify the number of duplicate acknowledgements relevant for investigations on the transmission control protocol.We show that our model reflects the burst/packet reordering pattern of simulated OBS networks very well. Applying our model in a network emulation scenario, enables investigations on real protocol implementations in network emulation environments. It therefore serves as a substitute for extensive TCP over OBS network simulations with a focus on burst reordering.     

A Novel Framework for IP DiffServ over Optical Burst Switching Networks

This paper presents a novel framework for IP Differentiated Services (DiffServ) over optical bursts witching (OBS), namely, DS-OBS. The network architecture, functional model of edge nodes and core nodes,the control packet format, a novel burst assembly scheme at ingress nodes and scheduling algorithm of core nodes are presented. The basic idea is to apply DiffServ capable burst assembly at ingress nodes and perform different per hop behavior (PHB) electronic treatments for control packets of different QoS class services at core nodes. Simulation results show that the proposed schemes can provide the best differentiated service for expedited forwarding (EF), assured forwarding (AF) and best effort (BE) services in terms of end-to-end delay, throughput and IP packet loss probability.     

Slotted Optical Burst Switching (SOBS) networks

In the paper, we study Optical Burst Switching (OBS) networks. Since OBS still suffers high loss ratio due to the lack of buffer at the OBS core routers, we study methods to reduce the loss without using optical buffers. We consider time-slotted OBS called Slotted OBS (SOBS), where routers are synchronized and only send fixed length bursts at the beginning of time slots. Our simulation results show that SOBS reduces the packet loss probability significantly. Moreover, we show that SOBS can be implemented with little or no additional cost and has other advantages such as providing better support for Quality of Service (QoS).     

Interleaved Traffic Splitting: A promising technique to solve False Timeout

In this paper, we analyze the False Timeout (FTO) problem that TCP flows suffered in OBS networks and propose Interleaved Traffic Splitting (ITS) to solve the problem. We show that the collision loss of ACK bursts may also cause FTO, which has been neglected by previous researchers. As TCP Sack is designed to recover from multiple packet losses, we find that a Sack flow can recover its data transmission without triggering retransmission timeout if packet loss is not too severe. This suggests limiting the number of packets carried by a single burst. In ITS, this is achieved by carrying out a parallel, interleaved burst assembly process at each ingress OBS edge router. We show that ITS tackles the FTO problem caused by the loss of both data and ACK bursts. Unlike other existing approaches, the ITS scheme requires only modification to the assembly/de-assembly mechanisms implemented at the edge routers. It does not add complexities to the network management or the router design. In this paper, both analytical and simulation results are presented to demonstrate the performance improvement of ITS. Our analysis further shows that the use of two parallel bursts is optimum for ITS.     

Performance analysis of an ingress switch in a JumpStart optical burst switching network

We consider an ingress optical burst switching (OBS) node employing the JumpStart signaling protocol. The switch serves a number of users, each connected to the switch with a fiber link that supports multiple wavelengths. Each wavelength is associated with a 3-state Markovian burst arrival process which permits short and long bursts to be modeled. We model the ingress switch as a closed multi-class non-product-form queueing network, which we analyze approximately by decomposition. Specifically, we develop new techniques to analyze the queueing network, first assuming a single class of customers, and subsequently multiple classes of customers. These analytical techniques have applications to general queueing networks beyond the one studied in this paper. We also develop computationally efficient approximate algorithms to analyze an ingress switch in the limiting case where the number of wavelengths is large. The algorithms have a good accuracy, and they provide insight into the effect of various system parameters on the performance of an ingress OBS switch.     

On using forward error correction for loss recovery in optical burst switched networks

An important issue in optical burst switched (OBS) networks is the loss of bursts at intermediate nodes due to contention. Such contention losses, usually do not mean a situation of congestion. In this paper, we propose for the first time, a loss recovery mechanism using Forward Error Correction (FEC) to recover bursts that are lost due to contention. Using FEC, for every K bursts, N − K redundant bursts are also sent to the destination. This redundancy can be used to recover from losses in the K data bursts. Our mechanism can also be used to recover from losses due to network component (link/node) failures. We demonstrate the effectiveness of our mechanism by comparing with no protection and 1 + 1 protection using simulation studies.     

A redundant overbooking reservation algorithm for OBS/OPS networks

Optical burst switch (OBS) has been a hot topic in the area of optical networks. OBS can realize statistic multiplexing while having the advantage of simplicity in deployment. A key issue in OBS is how to reduce the rate of the burst dropping caused by the absence of optical buffers or by the limited number of Fiber Delay Line (FDL). Existing work addresses this issue in the wavelength, time, or space domains. This paper proposes an algorithm, which works from a new domain to address this problem. Specially, it works by using the idle bandwidth in upstream links to transmit redundant copies of bursts to provide more sending chances at the downstream node. Simulation results are given to demonstrate the high performance of our algorithm.     

Algorithms for burst rescheduling in WDM optical burst switching networks

Wavelength division multiplexing (WDM) is a promising technology for realizing terabit networks. Optical burst switching (OBS) is a way to efficiently support bursty traffic on WDM-based optical Internet networks. In OBS networks, the control (header) and payload (data) components of a burst are sent separately with a time gap. The control packet first traverses the burst switching nodes and reserves suitable wavelengths on the links for the corresponding data burst by using a scheduling algorithm. Our work is motivated from the observation that the existing scheduling algorithms either have low computational complexity or high performance in terms of burst dropping probability, but not both simultaneously. Since the arrival of bursts is dynamic, it is highly desirable that the scheduling is done as quickly as possible. We develop scheduling algorithms which integrate the merits of both low computational complexity and high burst dropping performance. The key idea is to reschedule an existing burst by assigning a new wavelength to it keeping the burst arrival and leaving time unchanged in order to accommodate the new burst. We propose computationally simple rescheduling algorithms called on-demand burst rescheduling and aggressive burst rescheduling. The effectiveness of the proposed algorithms and the signaling overhead are studied through simulation experiments.     

On providing elastic QoS in optical burst switched networks

Integrated services schemes have not been used to support QoS in OBS networks, largely because of the high control overhead involved in monitoring bursts continuously at intermediate nodes. In this paper, we propose for the first time, an integrated services scheme to support elastic QoS in OBS networks. Our scheme relieves intermediate nodes of the burden of monitoring individual bursts continuously, thus largely decreasing the control overhead. We show how absolute bandwidth guarantees can be provided, and how bandwidth used by each connection can be made elastic. We demonstrate the effectiveness of our scheme using both analytical and simulation studies.     

Route optimization in optical burst switched networks considering the streamline effect

Route optimization in optical burst switching (OBS) networks is investigated in this paper. Two route optimization problems are studied. The first problem considers the network in the normal working state where all the links are working properly. The route for each flow is decided so as to minimize the overall network burst loss. The second problem considers the failure states apart from the normal working state. The primary and backup paths for each flow are determined in such a way to minimize the expected burst loss over the normal and failure states. We argue that route selection based on load balancing or the traditional Erlang B formula is not efficient because of an important feature called the streamline effect. We analyze the streamline effect and propose a more accurate loss estimation formula which considers the streamline effect. Based on this formula, we develop mixed integer linear programming (MILP) formulations for the two problems. Since the MILP-based solutions are computationally intensive, we develop heuristic algorithms. We verify the effectiveness of our algorithms through numerical results obtained by solving the MILP formulations with CPLEX and also through simulation results.     

Link scheduling state information based offset management for fairness improvement in WDM optical burst switching networks

In wavelength division multiplexed (WDM)-based optical burst switching (OBS) networks, bursts that traverse longer paths are more likely to be dropped compared to bursts that traverse shorter paths resulting in a fairness problem. Fairness here refers to having, for all ingress–egress node pairs in a network, a burst to have equal likelihood to get through independent of the hop length involved. In this paper, we develop a link scheduling state based fairness improvement method which can be used in a classless as well as a multi-class environment. The basic idea is to collect link scheduling state information and use it to determine the offset times for routes with different hop lengths. By using the online link state information, this method periodically computes and adapts the offset times needed, thus inherently accounting for the traffic loading patterns and network topological connectivity. It also ensures that the delay experienced by a burst is low and shorter-hop bursts are not over-penalized while improving the performance of longer-hop bursts. The effectiveness of the proposed method is evaluated through simulation experiments.     

光突发交换竞争解决机制研究

作为下一代互联网的关键技术之一的光突发交换技术已受到业界的广泛关注。本文在介绍光突发交换基本概念、特点的基础上,重点探讨了解决光突发交换网中突发数据包之间争夺链路资源问题的竞争解决机制,主要包括光缓存、波长转换、偏转路由以及突发分片等技术,对这些技术的优缺点进行了分析比较,并给出了一种偏转路由和突发分片技术结合的竞争解决方法。     

A novel TCP with dynamic Burst-Contention Loss notification over OBS networks

In this paper, a novel congestion control scheme with dynamic Burst-Contention Loss notifications in Optical Burst Switching (OBS) networks is proposed. The proposed scheme, called TCP-BCL, aims to handle various OBS bursty conditions that negatively affect TCP throughput performance and fairness. The basic design principle of the scheme is to tune the congestion control parameters α and β such that the congestion window sizes in the corresponding TCP senders can be adjusted with an explicit notification from the OBS edge node. The performance impact on TCP in terms of burst dropping due to random contention, which is also known as false congestion detection is considered and investigated. An analytical model is developed and further verified through extensive simulation.     

Correlating burst events on streaming stock market data

We address the problem of monitoring and identification of correlated burst patterns in multi-stream time series databases. We follow a two-step methodology: first we identify the burst sections in our data and subsequently we store them for easy retrieval in an efficient in-memory index. The burst detection scheme imposes a variable threshold on the examined data and takes advantage of the skewed distribution that is typically encountered in many applications. The detected bursts are compacted into burst intervals and stored in an interval index. The index facilitates the identification of correlated bursts by performing very efficient overlap operations on the stored burst regions. We present the merits of the proposed indexing scheme through a thorough analysis of its complexity. We also manifest the real-time response of our burst indexing technique, and demonstrate the usefulness of the approach for correlating surprising volume trading events using historical stock data of the NY stock exchange. While the focus of this work is on financial data, the proposed methods and data-structures can find applications for anomaly or novelty detection in telecommunication, network traffic and medical data.