Cost-effective combination of contention resolution/avoidance schemes in bufferless slotted OPS networks

Contention is a major problem for Optical Packed Switched (OPS) networks. Many studies have shown that to obtain a very small optical packet loss rate, a large number of specific contention resolution or contention avoidance hardware must be used. However, this may not be so cost-effective. Instead of using the same technique to achieve a very low packet loss rate, the idea of this paper is to use the combination of different contention avoidance and contention resolution schemes, but using a lower amount of each scheme, to reduce packet loss rate in slotted bufferless OPS networks. A number of cost-effective contention resolution and avoidance schemes are studied in order to decrease traffic loss and increase TCP throughput as a result. Designing a multi-fiber architecture that uses inexpensive shared-per-node wavelength converters and additional drop-ports can significantly reduce network-wide traffic loss. The lost traffic can also be retransmitted in the optical domain in order to have a loss-free OPS network. A cost model is also provided to obtain cost-effective combinations of fibers, wavelength converters and drop ports under a desirable TCP throughput and investment on network hardware. The effectiveness of the combined contention avoidance and resolution schemes are demonstrated under Internet traffic.     

Performance analysis of an integrated scheme in optical burst switching high-speed networks

A new integrated scheme based on resource-reservation and adaptive network flow routing to alleviate contention in optical burst switching networks is proposed. The objective of the proposed scheme is to reduce the overall burst loss in the network and at the same time to avoid the packet out-of-sequence arrival problem. Simulations are carried out to assess the feasibility of the proposed scheme. Its performance is compared with that of contention resolution schemes based on conventional routing. Through extensive simulations, it is shown that the proposed scheme not only provides significantly better burst loss performance than the basic equal proportion and hop-length based traffic routing algorithms, but also is void of any packet re-orderings.     

CORD: Optical packet-switched network testbed

We are implementing and investigating CORD, a 2.5 Gbit/s/λ WDM packet-switched network testbed. CORD features: (i) contention resolution optics (CRO), which consist of optical switches and delay lines to perform all-optical packet contention resolution; (ii) multichannel subcarrier multiplexed (MSCM) signaling to transmit an 80 Mbit/s control channel and 2.5 Gbit/s payload data on the same wavelength; (iii) networkwide distributed slot synchronization technique with maximum slot jitter of ± 6.5 ns; (iv) novel ultrafast signaling synchronization using delay-line phase alignment for data recovery within 4 bits; and (v) pilot-tone payload data synchronization for clock recovery within 16 ns.

In this article, we describe the CORD network testbed and discuss the performance and scaling potential of the technologies developed for CORD.     

Compact Optical WDM ATM Switch with an Aggregate 4-Tbit/s Throughput

We propose a novel scheme for interconnection of multiple high-speed (2.5 10 Gbit s) asynchronous transfer mode (ATM) streams through an optical wavelength division multiplexing (WDM) network with a total network capacity of up to 4 Tbit/s. The proposed architecture is based on placing the optical WDM portion of the network in a physically small area, i.e., one central office or in a single rack. This helps to avoid technological obstacles such as power budget, dispersion, and synchronization limitations as well as optical output buffering. The interconnection is an ATM packet switched network and provides optical contention resolution. We show that the implementation of such a network is possible using currently available optoelectronic technology. An optional extension of the network is proposed by a combination of WDM and space division multiplexing (SDM) technology. Simulation results are presented, indicating network throughput of up to 100 %.     

Emerging Trends in Fiber Optic Networks

We propose a novel scheme for interconnection of multiple high-speed (2.5 10 Gbit s) asynchronous transfer mode (ATM) streams through an optical wavelength division multiplexing (WDM) network with a total network capacity of up to 4 Tbit/s. The proposed architecture is based on placing the optical WDM portion of the network in a physically small area, i.e., one central office or in a single rack. This helps to avoid technological obstacles such as power budget, dispersion, and synchronization limitations as well as optical output buffering. The interconnection is an ATM packet switched network and provides optical contention resolution. We show that the implementation of such a network is possible using currently available optoelectronic technology. An optional extension of the network is proposed by a combination of WDM and space division multiplexing (SDM) technology. Simulation results are presented, indicating network throughput of up to 100 %.     

Integrated Contention Resolution and Control Algorithm for Optical Burst Switched Networks

Abstract

This article compares the conventional and proposed integrated contention resolution and control algorithm in optical burst switching with respect to burst loss probability and network throughput. Results have shown that the proposed approach behaves well in practice and responds quickly to any change in network status, while improving the overall network performance. It is shown that the proposed algorithm (ICRCA) not only provides significantly better burst loss performance than the conventional algorithms, but is also void of any packet re-orderings.     

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.     

Hybrid buffering architecture for packet contention resolution of an optical packet switch

Packet contention is a major issue in optical packet switching network and it is not a trivial task to resolve due to lack of optical RAM technology. In order to resolve contention optical buffering approach is used using fiber delay lines (FDLs). Yet there is a heavy packet loss rate due to unavailability of output port and free FDLs. This paper proposes a hybrid buffering architecture using feed-forward and feedback shared FLDs to resolve packet contention resolution of an optical packet switch. Feed-forward FDLs are used as primary buffer and feedback FDLs are implemented as supplementary buffer. Simulation result shows that proposed hybrid buffering switch achieves packet loss rate between 10⁻¹ and 10⁻² at heavy traffic load (ρ = 0.9) for a 32 × 32 switch using different FDL length.     

Novel applications of one-dimensional photonic crystal in optical buffering and optical time division multiplexing

Novel applications of one-dimensional photonic crystal in optical buffering and optical time division multiplexing are suggested. These one-dimensional photonic crystal optical buffers can store data packets temporarily for a certain period of time, which depend on the lattice parameters. By changing the lattice parameters the data hold time can be changed in a desired way. This type of optical buffer finds potential application in contention resolution in optical switch of a router, in a packet-switched optical network and in design of novel optical time division multiplexers (OTDM).     

All-optical implementations for high-capacity TDMA networks

In this article we show how optical technology can allow the design of new optical devices that are able to perform some network functions in order to treat very high bit rate signals (100 Gbit/s). The multiplexing technique that we take into account is the Time Division Multiple Access (TDMA), and the network functions we consider are multiplexing, demultiplexing, synchronization, packet decoding, routing, and resolution of packet contention.

In order to show how these new optical devices can improve the network performance we propose two different network topologies: the first concerns a TDMA star network where the signal information is simultaneously broadcast to all users, while the second is a multihop network. The former is useful mainly for circuit switching, while the latter is suitable for packet switching.

Soliton propagation is used in order to avoid the problem of fiber chromatic dispersion.     

一种反馈FDL结构竞争解决丢包率的研究

对反馈FDL结构的光分组交换竞争解决方案建立了数学模型并进行了理论分析,推导出了在反馈FDL输入分组比输入光纤输入分组具有更高输出优先级时的系统丢包率公式,对系统丢包率与负载、输入光纤端口数和FDL数目的关系进行了数值计算和讨论.结果表明：由于FDL缓存分组的概率与输入分组负载的非线性关系导致了反馈FDL结构在低负载时对丢包率的改善非常明显,对高负载的改善却十分有限.随着FDL数目的增加,对系统丢包率的改善不会趋于一个极限值,这是与使用波长转换器进行竞争解决的不同之处,因此使用反馈FDL结构可以降低波长转换器的丢包率极限.     

A novel differentiated services supporting scheme for optical burst switched networks

In this letter, we analyze the drawback of tail-dropping contention resolution in optical burst switched networks. Once contention occurs, we adopt modified head-dropping policy to resolve contention. This policy drops the head of the contending burst only if the overlapping region of the two bursts is less than the whole contending burst size, otherwise drops the whole contending burst. In order to have a better support of differentiated service, a new burst assembly policy, namely, Priority-based proportional mixed burst assembly, is proposed. Simulation results show that the proposed scheme performs very well in terms of performance metrics such as the times of contention and packet loss probability.     

Fairness and throughput performance of infrastructure IEEE 802.11 networks with hidden-nodes

The fairness behavior and throughput performance of IEEE 802.11 distributed coordination function and request-to-send/clear-to-send channel access scheme in the presence of hidden nodes are investigated. A mathematical model which accurately predicts a user’s throughput performance and packet collision probability in non-saturated traffic and asymmetric hidden node environments is developed. The model allows us to see many interesting results in networks with hidden nodes. In an asymmetric hidden node network environment, the network fairness performance depends on the traffic load. In low traffic conditions, users get their fair share of the resources. However, in moderate-to-high traffic conditions, users that experience less number of hidden nodes dominate the network, causing badly located stations in a network to starve. In addition, the performance of request-to-send/clear-to-send channel access scheme, which is developed as a solution to hidden node problem, in networks with hidden nodes, is also estimated. It is shown that request-to-send/clear-to-send contention resolution scheme greatly improves the network fairness performance in hidden node scenarios. The developed model enables us to more accurately estimate the performance of practical wireless local area networks, where hidden node occurrence is common. Theoretical analysis presented in the paper is validated with simulation results.     

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.     

A cognitive MAC protocol for QoS provisioning in ad hoc networks

In this paper, we consider an ad hoc network overlaying a legacy time-division multiple access (TDMA) system. This kind of ad hoc and infrastructure-based coexisting architecture can have an important application for the future cognitive radio (CR) network. To establish an overlaying ad hoc network in the presence of primary users, the medium access control (MAC) protocol shall achieve high spectrum utilization, avoid interfering the primary user and establish the link quickly. To this end, we propose four enhanced mechanisms for the carrier sense multiple access with collision avoidance (CSMA/CA) MAC protocol: (1) a neighbor list establishment mechanism for recognizing spectrum usage opportunities, (2) a set of contention resolution methods to reduce the collision and delay variance, (3) an invited reservation procedure for meeting the delay requirements of real-time traffic, and (4) a distributed frame synchronization mechanism for coordinating transmission without a centralized controller. Compared to the legacy IEEE 802.11 MAC protocol, the proposed CSMA/CA MAC protocol enhancement can improve the system throughput by 50% through analysis and NS-2 simulations, while keeping the dropping rate lower than 2% for delay-sensitive traffic. Furthermore, the standard deviation of the access delay is reduced by five times. With these QoS enhanced mechanisms, the proposed cognitive CSMA/CA MAC protocol can allow an ad hoc network to coexist with the legacy TDMA system.     

光突发交换网中一种新的有优先权的冲突解决方案

提出了一种解决不同优先级突发包之间资源竞争的方案,分析了该方案下不同优先级的性能(时延和丢包率) .研究结果表明：高优先级突发包的平均时延和丢包率都远小于低优先级突发包,因此该方案能为高优先级突发包提供很好的QoS保障.     

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.     

A maximum-efficiency-first multi-path route selection strategy for optical burst switching networks

In this paper, the impact of a path selection on other existing paths in optical burst switching (OBS) networks is studied by analyzing the contention among different traffic streams and the interaction between the route selection and traffic load balance. The results show that there exists a mutual reinforcement interaction among the traffic load of a path, the path burst loss ratio and the contention ability of the path when burst loss ratio based multi-path selection strategies are adopted, which may increase the unbalance of traffic and lead to severe congestion further. A maximum-efficiency-first multi-path selection strategy, which considers the performance of the burst flows and the impact of a path selection on existing OBS paths at the same time by a combined metric of route efficiency, is proposed to maximize the utility of the burst flows and minimize the increment of lost throughput on the path. The performance of the proposed multi-path selection strategy is evaluated through simulation. The results show that the presented strategy obviously outperforms the least burst loss ratio strategy and shortest path first strategy in terms of the burst loss ratio in the practical unbalanced background traffic, especially when the network is heavily loaded.     

The Design of the M-B-Quadro Optical Switch and Its Access Control Strategies

This paper proposes a new simple contention resolution switching architecture, M-B-Quadro, and its underlying access control strategies. By incorporating delay and buffer lines, the switching node can effectively obtain very low packet deflection probability.     

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.