A new flexible and enhancing bandwidth utilization burst dropping technique for an OBS network

Optical burst switching (OBS) has been proposed as a competitive hybrid switching technology to support the next generation optical Internet. However, due to their one-way resource reservation mechanism, OBS networks experience high bursts (thus packets) loss rate. In OBS networks, the contention is resolved either by dropping one of the contending bursts or more efficiently by dropping from one of the contending bursts only the parts that overlap with the other bursts. In both situations, only one data source will suffer the data loss in favor to the other. In this paper, a new burst flexible and enhancing bandwidth utilization burst dropping technique has been proposed for contention resolution in optical burst switched networks. When contention occurs, any part of a contending burst could be dropped, instead of only the head or tail of bursts. The proposed dropping scheme makes bandwidth utilization more efficient and flexible. Simulation results show that the proposed dropping scheme performs better than existing burst dropping schemes.     

Performance enhancement of optical burst switched networks

Optical burst switching (OBS) is an optical switching paradigm which offers a good tradeoff between the traditional optical circuit switching (OCS) and optical packet switching (OPS) since it has the relatively easy implementation of the first and the efficient bandwidth utilization of the second. Hence, OBS is a promising technology for the next generation optical Internet. A buffer-less OBS network can be implemented using ordinary optical communication equipment without the need for either wavelength converters or optical memories. In an OBS network, burst-loss performance is a critical concern. In OBS, the data-burst transmission is delayed by an offset time (relative to its burst control packet (BCP), or header) and the burst follows its header without waiting for an acknowledgment for resource reservation. Thus, a burst may be lost at an intermediate node due to contention, which is generally resolved according to the local routing and bandwidth information. The routing table maintained in each OBS node is generally pre-computed and fixed to forward the data bursts. Such a static forwarding feature might have limited efficiency to resolve contentions. Moreover, a burst may be lost and the network may be congested when a network element (e.g., fiber link) fails. In this paper, an efficient integrated scheme based on dynamic routing and burst segmentation has been proposed to improve reliability of data transport and network load balancing in optical burst switched networks. Simulation results demonstrate that the proposed approach reduces effectively blocking probability and hence contention. Further, it provides end-to-end throughput performance also. Hence, it establishes an appropriate tradeoff between loss rate and end-to-end throughput.     

Burst dropping policies in optical burst switched network

Optical burst switching (OBS) has been proposed as a competitive switching technology to support the next generation optical Internet. However, due to their one-way resource reservation mechanism, OBS networks experience high bursts (thus packets) loss rate. In OBS networks, the contention is resolved either by dropping one of the contending bursts or more efficiently by dropping from one of the contending bursts only the parts that overlap with the other bursts. In both situations, only one data source will suffer the data loss in favor to the other. In this paper, a novel burst dropping policy based on even selection of burst (BDPES) has been proposed in conjunction with an appropriate mechanism to provide differentiated service in order to support the quality of service (QoS) requirements of different applications. In the proposed burst dropping policy, the dropped segments are selected evenly from both contending bursts and the truncated bursts are guaranteed to be larger than the minimum burst-length allowed by the network. Furthermore, the proposed policy is enhanced via a flow control mechanism. Simulation results show that the performance of proposed policy is better than existing burst dropping mechanisms in terms of reducing burst (packets) loss rate.     

Analysis of burst/packet assembly techniques in high-speed optical switching network

In the Optical Burst Switching (OBS) Network, the burst assembly technique is one of the challenging issues in the implementation of the system. It has the influence on the burst characteristic, which gives an impact on the network performance. Burst assembly is the process of assembling incoming data from the higher layer into bursts at the ingress edge node of the OBS network. The burst assembly mechanism must then place these packets into bursts based on some assembly policy. In this paper, the OBS system performance has been observed in simulated 12-node network based on Just-Enough-Time (JET) reservation protocol with various burst assembly techniques under the standard drop policy (DP) and the segmentation policy for contention resolution. The simulation results show that the performance of the proposed Adaptive-Threshold with Fixed Maximum Time Limitation (ATH-FMTL) burst assembly scheme is better than conventional burst assembly schemes in terms of loss probability and average assembly delay. Also, the proposed scheme avoids a sudden increase in the burst size and makes the burst sent out smoother as compared to conventional schemes.     

一种适用于光突发交换的区分型资源预留机制

将边缘结点突发汇聚算法与核心结点资源预留机制有机结合,提出了一种适用于光突发交换的区分型资源预留机制.引入“突发流”的概念,在边缘结点采用基于线性预测的突发汇聚算法将输入IP分组汇聚为单个突发或突发流;在核心结点引入“搭载请求”的思想,对单个突发和突发流采用不同的资源预留方案.仿真结果表明区分型资源预留机制可以明显改善光突发交换网络的丢失性能.     

Congestion prevention for reliable OBS

It is known that Internet traffic exhibits a structural self-similarity over a wide range of time scales. Existing performance evaluation studies in optical burst switching (OBS) networks show high contention performance degradation in the nodes under correlated traffic. Due to its buffer-less nature, OBS efficiency can be reduced by resource contention leading to burst loss. Several methods have been proposed to address this problem, most of them relying on reactive mechanisms, which increase the complexity of core nodes, hampering scalability. In this paper to have congestion prevention, an efficient scheme incorporating delayed reservation decision has been proposed which not only offers reduction in resource contention by maintaining the same node complexity as that in general OBS networks with optical buffers but also provides improvement in system's throughput. Simulations show the proposed scheme has better performance than existing schemes in terms of burst loss probability.     

An optimal protection and restoration scheme (OPARS) for optical networks

Protection and restoration are critical network design issues for optical networks since even a single failure for a short duration may result in huge data loss due to the large capacity of optical fibers. However, few studies have been done on these issues for optical burst switching (OBS) networks. Protection and restoration are essential mechanisms for guaranteeing more reliable traffic delivery services. But it is not easy to apply existing mechanisms to optical burst switching (OBS) networks due to its one-way reservation signaling and the statistical burst multiplexing. Thus, to achieve the high transmission performance and reliability simultaneously, unique properties of OBS must be considered in the design of protection scheme. In this paper, an optimal protection and restoration scheme (OPARS) has been introduced that not only optimizes the number of provisioned protection wavelengths adaptively based on the traffic load as well as the quality of service (QoS) requirements of bursts in high speed networks but also minimizes burst loss rates. In addition, the proposed scheme has been used as an efficient contention resolution technique. The simulation results verify that the proposed scheme improve the network resource and channel utilization while guaranteeing the targeted protection reliability and QoS requirements of bursts.     

光突发交换网络试验平台

研究并实现了几种光突发交换网络的关键技术,包括高速的突发组装技术、突发调度技术及突发光发射及接收技术等,其中突发接收具有较高的灵敏度和小于80 ns的时钟数据恢复时间.在这些技术的基础上,建立了一个灵活且可扩展的光突发交换网络实验平台.在OBS网络平台上进行了TCP性能评估实验和多QoS业务传输实验。实验结果表明光突发网络中丢包率严重影响其上TCP的性能,但若丢包率小于0.1%,则TCP性能可得到一定程度的保证.光突发交换网络实验平台上的TCP传输实验还表明了OBS物理层带来的额外延时对上层TCP带宽有极大的影响.实验结果还验证了OBS网络中的QoS保证机制.     

TCP在光突发交换试验网络中性能的实验研究

在光突发交换试验网络中对TCP的性能进行了实验研究.首先研究了丢包对网络性能的影响,表明突发包丢失将导致TCP吞吐量的快速下降,并且丢包率越高,可用的TCP传输带宽越窄.然后分别详细研究了OBS试验网络中的延时损伤和报文段关联增益,以及对TCP传输性能的影响.最后综合考虑这些因素.实验结果表明,在本OBS试验网络中存在一个不随丢包率变化的最优化突发包组装时间250us使得可用TCP带宽最大化.为了最大限度地提高TCP的传输性能,组包时间应该选择等于或稍大于这个最优值.     

Contention reduction and service differentiation in OBS networks

Optical burst switching (OBS) has been proposed to be a competitive switching technology for wavelength division networks (WDM) networks. In this switching technique, single burst loss due to contention influences loss of multiple data. Thus, burst loss ratio (BLR) is the main deciding factor for determining the performance of an OBS network. Also, inefficient data channel scheduling algorithm causes burst loss in OBS. In addition to this, the same service to all model of the current Internet is inadequate for the diverse quality of service expectations of Internet applications and users. In this paper, an efficient technique is proposed in which data burst is assembled from several Internet protocol (IP) packets in such a manner that the number of IP packets is changed according to the traffic load. In the proposed scheme, the burst is segmented because the segment located at the end of the contended burst has a greater chance of surviving contention (as the dropped segments are those at the beginning of the contending burst). Thus, the most important (or higher priority) information is enveloped in the last segmented. Further to prevent resource wastage due to over admitting of bursts, the proposed scheme is extended by admission control test for an output link without a fiber delay line (FDL) buffer. Also, modified latest available unscheduled channel with void filling (LAUC-VF) scheduling algorithm utilizing MPLS has been used to provide a scalable and manageable architecture for service differentiation (DiffServ) in IP networks. Simulation results demonstrate that the proposed technique has reduced burst loss rate and better quality of service (QoS) performance in comparison to existing techniques.     

光突发交换中交换矩阵配置时间的影响研究

光突发交换是近几年出现的一种很有前途的交换技术。在光突发交换网络的核心节点中,光交换矩阵是一个关键部件,其配置时间影响到光突发交换网络的性能。这种影响表现在对数据信道可用时间施加了限制。在考虑光交换矩阵配置时间的基础上给出了修正后的LAUC算法,并通过计算机仿真研究了这种配置时间对光突发交换性能的影响。结果表明,光交换矩阵配置时间的增大会导致输出数据信道利用率的降低,进而增大了数据丢失率。     

An efficient scheme for optimizing channel utilization in OBS networks

Optical burst switching (OBS) is an emerging technology that allows variable size data bursts to be transported directly over DWDM links. In order to make OBS a viable solution, the wavelength scheduling algorithms need to be able to utilize the available wavelengths efficiently, while being able to operate fast enough to keep up with the burst incoming rate. Unfortunately, horizon scheduling cannot utilize the voids created by previously scheduled bursts, resulting in low bandwidth utilization. To date, Min-SV is the fastest scheduling algorithm that can schedule wavelengths efficiently. However, its complexity is O (log m) and it requires 10 log (m) memory accesses to schedule a single burst. This means that it can take upto several microseconds for each burst request, which is still too slow to make it a practical solution for OBS deployment. In this paper, an efficient scheme has been proposed for optimizing channel utilization in OBS networks. In the proposed approach, a burst is represented by an interval of time. The process of scheduling a number of bursts, thus, turns to be a process of fitting a set of the corresponding time intervals on a channel time line that represents a channel-time resource. By doing so, the scheduling process can be formulated as a combinatorial optimization problem. Then, graph theory is applied to schedule as many non-overlapping intervals as possible onto the channel time line. The underlying concept of the proposed scheduling scheme is that of briefly delaying the scheduling of a burst so that a much better decision can be made about a number of bursts all-together. This scheme is shown, through simulations, to improve performance in terms of burst loss probability, channel utilization, fairness-control and data throughput over existing schemes. Thus the proposed scheme is well suited for high performance networks in terms of reliability.     

An optimal burst assembly approach employing traffic shaping (OBATS) for OBS

Optical burst switching (OBS) aims at combining the strengths of packet and circuit switching and is considered as a promising technology for implementing the next generation optical Internet, required to cope with the rapid growth of Internet traffic and the increased deployment of new services. In this paper, an optimal burst assembly approach employing traffic shaping (OBATS) for OBS networks has been proposed in order to improve network performance in terms of reduced blocking probability, congestion control and better utilization of bandwidth. Particularly, the proposed scheme aims at reducing the average delay experienced by the packets during the burstification process in optical burst switched (OBS) networks, for a given average size of the bursts produced. Reducing the packet burstification delay, for a given average burst size, is essential for real-time applications; correspondingly, increasing the average burst size for a given packet burstification delay is important for reducing the number of bursts injected into the network and the associated overhead imposed on the core nodes. Simulation results show that the proposed burst assembly approach gives better network performance in terms of burst drop, resource contention and delay as compared to conventional burst assembly approaches.     

Performance analysis and improvement of loss recovery mechanisms in star OBS networks

In OBS networks, burst loss affects negatively the performance of the higher layers. Proactive loss recovery mechanisms, such as burst cloning, have the advantage of low burst delay but it suffers from low bandwidth utilization. However, reactive loss recovery mechanisms, such as burst retransmission, have the advantage of high bandwidth utilization but at the cost of high burst delay. In this paper, we present an analysis of this trade-off and we propose two new schemes to improve bandwidth utilization while keeping burst delay as low as possible in star OBS networks. The first scheme controls the retransmissions. The second scheme combines burst cloning and burst retransmission mechanisms. Analytical and simulation results show that the both schemes achieve high bandwidth utilization. The results confirm also that compared to basic burst retransmission scheme, the first scheme reduces burst delay only at moderate and high load, however, the second scheme reduce delay at every load.     

OBS网络中基于优先级与突发包分割的偏射路由机制

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与突发包分割的偏射路由机制.当冲突发生时,首先基于突发包的优先级进行"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根据参数可调的偏射路由机制被偏射到最佳偏射路径上.仿真结果表明,该机制能够有效地降低整个网络的丢包率和端到端的延时,并且得到高优先级突发包的丢失率和延时低于低优先级突发包.由此可知,基于优先级与突发包分割的偏射路由机制能够有效地解决突发包的冲突问题,从而提高整个OBS网络的性能.     

A well-aware resource reservation strategy TAW in the Optical Burst Switched System

For the Optical Burst Switched (OBS) System, a new resource reservation strategy TAW⁺ is presented in the Intra-Domain Network Statue Model (INSM). By promptly using the control signal channel to update the INSM, better decisions are made in selecting optical path and assigning wavelength at each OBS network edge node, which can make the node to avoid reserving those being used link resources. Besides, a time slot is introduced to detect the latent collision, which not only can achieve the goal in preventing the forthcoming collision effectively, but also can better support multi-priority QoS. Furthermore, Virtual Configuration Table (VCT) at the network core node is further proposed to resolve collisions without bandwidth wastage. The analysis and simulation results verify the feasibility of the proposed strategy in the OBS network, show the enhancing of the network state awareness capability at edge node in lack of the optical conversion capability and optical buffer, and improve the effect on the data burst drop probability and QoS supports.     

A new burst assembly technique for supporting QoS in optical burst switching networks

This letter proposes a new burst assembly technique for supporting QoS in optical burst switching (OBS) networks. It consists of the adaptive-threshold burst assembly mechanism and QoS-based random offset-time scheme. The assembly mechanism, which is fit well to multi-class burst assembly, not only matches with IP QoS mechanism based on packet classification, and also utilizes fairly and efficiently assembly capacity. Based on token-bucket model and burst segment selective discard (BSSD), the offset-time scheme can smooth the traffic to support OBS QoS. The simulation results show that the technique can improve the performance in terms of packet loss probability (PLP).     

一种新型的突发汇聚算法研究

分析了现有的突发汇聚算法,同时针对现有汇聚算法的一些特点,提出了一种新型突发包汇聚算法,可以实现在不同网络负载的情况下,根据到达边缘节点的速率同时结合网络的性能(丢包率),动态的调整突发包汇聚的门限值,从而实现了智能组包,克服了原有算法简单,不灵活的缺点.通过仿真结果可以得知,该算法可以明显改善光突发交换网络的丢包率和时延性能,能够很好地支持实时性要求很高的数据业务.     

Performance analysis of an improved burst-outputted model for an OBS core router

Differentiated probability outputted scheme (DPOS) is an improved burst-outputted paradigm in optical burst switching (OBS) core routers. In this paper, the blocking performance for multi-priority traffic in a DPOS applied OBS core router with limited buffers has been analyzed and discussed firstly. Several simulation results indicted that DPOS had a better performance in blocking than the outputted model presented in the previous work had. Besides, our proposed scheduling mechanism can supported the quality-of-service (QoS) efficiently for OBS networks.     

A QoS-Guanranteed Scheduling Algorithm with High Throughput for Edge Nodes of Optical Burst Switching Networks

A scheduling algorithm for the edge nodes of optical burst switching (OBS) networks is proposed to guarantee the delay re quirement of services with different CoS (Class of Service) and provide lower burst loss ratio at the same time. The performance of edge nodes based on the proposed algorithm is presented.