A Technique to Minimize Contention in Optical Burst Switching Networks

Optical burst switching (OBS) is the new switching technique for next generation optical networks. However, there are certain issues such as burst aggregation, scheduling, contention resolution and QoS that needs to be addressed in OBS. This thesis is an attempt to address the burst scheduling and burst contention in OBS networks. Several scheduling algorithms have been proposed in the literature, which can be categorized into Horizon and Void lling scheduling algorithm. Void lling algorithms perform better because they exploits void within a channel for scheduling. Reported void lling algorithms - Latest available unscheduled channel with void lling (LAUC-VF) and Minimum end void (Min-EV) - do not consider the void duration in scheduling. In this thesis we propose a new scheduling algorithm called Best Fit Void Filling (BFVF), which consider both void duration and incoming burst length to nd an optimal void channel. We simulate our proposed scheme using obs-ns simulator and compared with LAUC-VF and Min-EV algorithm. Result shows that the burst loss ratio is lower and channel utilization is higher in our proposed scheme

A Priority Based Optical Header Contention Resolution in Optical Burst Switching Networks

OBS is a promising switching paradigm for the next-generation Internet.In OBS, data packets are assembled into variable size data burst which are transmitted optically over Dense Wavelength Division Multiplexing(DWDM)networks without O/E/O conversion. The control packet is sent before the data burst to reserve resources and configure switches along the path .The control packet is sent along the separate control channel and goes through O/E/O conversion. We have discussed various OBS signalling protocols and Burst Scheduling Algorithms. As the data channel bandwidth will grow it will lead to the overloading of the control path. In this thesis we have proposed an algorithm to resolve the contention of the optical header. The algorithm assigns the priority to each control packet arriving at the same time .The control packet with highest priority is selected for processing. Simulation results have shown that the technique is effective in improving the throughput

QoS Considerations in OBS Switched Backbone Net-Works

Optical Burst Switching (OBS) was proposed as a hybrid switching technology solution to handle the multi-Terabit volumes of traffic anticipated to traverse Future Generation backbone Networks. With OBS, incoming data packets are assembled into super-sized packets called data bursts and then assigned an end to end light path. Key challenging areas with regards to OBS Networks implementation are data bursts assembling and scheduling at the network ingress and core nodes respectively as they are key to minimizing subsequent losses due to contention among themselves in the core nodes. These losses are significant contributories to serious degradation in renderable QoS. The paper overviews existing methods of enhancing it at both burst and transport levels. A distributed resources control architecture is proposed together with a proposed wavelength assignment algorithm

PI-OBS: a Parallel Iterative Optical Burst Scheduler for OBS networks

This paper presents the PI-OBS algorithm, a parallel-iterative scheduler for OBS nodes. Conventional schemes are greedy in the sense that they process headers one by one. In PI-OBS, all the headers received during a given time window are jointly processed to optimize the delay and output wavelength allocation, applying void filling techniques, and allowing traffic differentiation. Results show a similar or better performance than the LAUC-VF algorithm, commonly used as a performance bound for OBS schedulers. The PI-OBS scheduler has been designed to allow parallel electronic implementation similar to the ones in VOQ schedulers, with a deterministic response time.This research has been partially supported by the MEC projects TEC2007-67966-01/TCM CON-PARTE-1, and TEC2008-02552-E, and it is also developed in the framework of "Programa de Ayudas a Grupos de Excelencia de la R. de Murcia, F. Séneca"

An assembly and offset assignment scheme for self-similar traffic in optical burst switching

Includes bibliographical references.Optical Burst Switching (OBS) is a viable technology for the next generation core network. We propose an FEC-assembly scheme that efficiently assembles self-similar traffic and a Pareto-offset assignment rather than a constant offset assignment. Two buffers, a packet buffer and a burst buffer, are implemented at the Label Edge Router (LER), buffering traffic in the electronic domain. The assembler, between the packet and burst buffers, is served by the packet queue while the assembler serves the burst queue. We outline advantages of why burst assembly cannot be implemented independent of offset assignment. The two schemes must be implemented in a complementary way if QoS is to be realized in an OBS network. We show that there is a direct relation between OBS network performance with burst assembly and offset assignment. We present simulation results of the assembly and offset assignment proposals using the ns2 network simulator. Our results show that the combination of the proposed FEC-Based assembly scheme with the proposed Pareto-offset assignment scheme give better network performance in terms of burst drop, resource contention and delay. Key to any traffic shaping is the nature traffic being shaped. This work also compares performance of both traditional exponential traffic with realistic Self-Similar traffic of Internet traffic on the proposed assembly and offset assignment schemes. In our simulations, we assume that all Label Switch Routers (LSR) have wavelength converters and are without optical buffers. We use Latest Available Unused Channel with Void Filling (LAUC-VF) scheduling scheme and use Just Enough Time (JET) reservation scheme

Cost functions in optical burst-switched networks

Optical Burst Switching (OBS) is a new paradigm for an all-optical Internet. It combines the best features of Optical Circuit Switching (OCS) and Optical Packet Switching (OPS) while avoidmg the mam problems associated with those networks .Namely, it offers good granularity, but its hardware requirements are lower than those of OPS. In a backbone network, low loss ratio is of particular importance. Also, to meet varying user requirements, it should support multiple classes of service. In Optical Burst-Switched networks both these goals are closely related to the way bursts are arranged in channels. Unlike the case of circuit switching, scheduling decisions affect the loss probability of future burst This thesis proposes the idea of a cost function. The cost function is used to judge the quality of a burst arrangement and estimate the probability that this burst will interfere with future bursts. Two applications of the cost functio n are proposed. A scheduling algorithm uses the value of the cost function to optimize the alignment of the new burst with other bursts in a channel, thus minimising the loss ratio. A cost-based burst droppmg algorithm, that can be used as a part of a Quality of Service scheme, drops only those bursts, for which the cost function value indicates that are most likely to cause a contention. Simulation results, performed using a custom-made OBS extension to the ns-2 simulator, show that the cost-based algorithms improve network performanc

Effect of burst length on loss probability in OBS networks with void-filling scheduling

Cataloged from PDF version of article.Optical burst switching (OBS) is a new transport architecture for the next generation optical internet infrastructure which is necessary for the increasing demand of high speed data traffic. Optical burst switching stands between optical packet switching, which is technologically difficult, and optical circuit switching, which is not capable of efficiently transporting bursty internet traffic. Apart from its promising features, optical burst switching suffers from high traffic blocking probabilities. Wavelength conversion coupled with fiber delay lines (FDL) provide one of the best means of contention resolution in optical burst switching networks. In this thesis, we examine the relation between burst loss probability and burst sizes for void filling scheduling algorithms. Simulations are performed for various values of the processing and switching times and for different values of wavelengths per fiber and FDL granularity. The main contribution of this thesis is the analysis of the relationship between burst sizes and processing time and FDL induced voids. This in turn creates a better understanding of the burstification and contention resolution mechanisms in OBS networks. We show that voids generated during scheduling are governed by the FDL granularity and the product of the per-hop processing delay and residual number of hops until the destination. We also show that differentiation between bursts with different sizes is achieved for different network parameters and a differentiation mechanism based on burst lengths is proposed for OBS networks.Kamçı, Ahmet KerimM.S

Flexible simulators for OBS network architectures

Since the OBS paradigm has become a potential candidate to cope with the needs of the future all optical networks, it has really caught the attention from both academia and industry worldwide. In this direction, OBS networks have been investigated under many different scenarios comprising numerous architectures and strategies. This heterogeneous context encourages the development of flexible simulation tools. These tools should permit both an easy integration of any possible new network protocol design and a rapid adaptation to different performance target goals. In this paper, we present two OBS network simulators, namely, a C-based simulator (ADOBS) and our novel Java-based simulator (JAVOBS). We compare their performances and we provide some exemplary results that point out remarkable flexibility that can be achieved with the JAVOBS simulator

A new adaptive burst assembly algorithm for OBS networks considering capacity of control plane

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2008.Thesis (Master's) -- Bilkent University, 2008.Includes bibliographical references leaves 55-57.Recent developments in wavelength-division multiplexing (WDM) technology increase the amount of bandwidth available in fiber links by many orders of magnitude. However, this increase in link capacities is limited by the conventional electronic router’s capability. Optical burst switching (OBS) has been proposed as a promising and a short-term solution for switching technology to take advantage of increased capacity of optical links. The congestion in OBS control plane and the adaptive burst assembly algorithms are two important research topics that are among the most effective factors determining the performance of OBS networks. These two problems have been separately studied in the literature so far. It has been shown that contending bursts at a core optical switch in an OBS network may experience unfair loss rates based on their residual off- set times and burst lengths, that are called path length priority effect (PLPE) and burst length priority effect (BLPE), respectively. In this thesis, we propose a new adaptive timer-based burst assembly algorithm (ATBA) which uses loss rate measurements for determining the burstification delays of traffic streams in order to mitigate the undesired effects of PLPE and BLPE. ATBA distributes the burst generation rates of traffic streams at an ingress node such that total rate of generated bursts is constant in order to constrain the congestion in the control plane. Without ATBA, the fairness index drops to 76% when per hop processing delay (PHPD) is increasing. With ATBA, the fairness index drops only to 85% with increasing PHPD. It is also shown that the total goodput of the OBS network improves by 5% compared with the case without ATBA.Çırak, İsmailM.S