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.

An efficient dynamic distributed optical link establish method in intelligent all-optical networks

In this article, an efficient, fast, and dynamic distributed optical link setup method is proposed. Two kinds of novel optical fast link release mechanisms (Ahead and Timeout Release) are presented for an optical-link establishment. They can dramatically reduce the blocking probability. For dynamic routing detection, a new kind of dynamic weighted Dijkstra algorithm (DW-DA) along with dynamic optical link load balancing is described. A variable mutation and crossover rates of a genetic algorithm (VMCR-GA) is used for fast wavelength assignment with two-novel-wavelength assignment rules in a wavelength relationship graph, which can reduce the necessary wavelengths and link establishment time. Through simulation giving the blocking probability and the time for link establishment on several well-known networks, the effectiveness of this method has been verified. The blocking probability of the network can be reduced significantly below that of normal routing and wavelength assignment (RWA). Furthermore, the calculating time for reaching the minimum blocking probability can be reduced dramatically.

XCP-based transmission control mechanism for optical packet switched networks with very small optical RAM

According to a famous rule-of-thumb, buffer size of each output link of a router should be set to bandwidth-delay product of the network, in order to achieve high utilization with TCP flows. However, ultra high speed of optical networks makes it very hard to satisfy this rule-of-thumb, especially with limited choices of buffering in the optical domain, because optical RAM is under research and it is not expected to have a large capacity, soon. In this article, we evaluate the performance of our explicit congestion control protocol-based architecture designed for very small Optical RAM-buffered optical packet switched wavelength division multiplexing networks with pacing at edge nodes in order to decrease the required buffer size at core nodes. By using a mesh topology and applying TCP traffic, we evaluate the optical buffer size requirements of this architecture and compare with a common proposal in the literature.

All-optical cross-connect using feed-forward optical buffers with and without QoS: an analysis

An analytical model is derived to evaluate the performance of an optical switch using a feed-forward fiber delay line (FDL) per output for contention resolution. Two different forwarding algorithms for the switch are presented and evaluated: a simple forwarding algorithm (SFA) that is easier to implement, and an enhanced algorithm that provides better performance in terms of both packet loss probability and packet delay. The analytical model can be utilized with both packet and burst switching schemes to characterize the performance of the proposed architecture. Results show that the proposed architecture reduces the packet loss probability compared to that without FDLs. Finally, the same architecture is shown to be capable of supporting Quality of Service (QOS).

Restoration in wavelength-routed optical networks by means of ant colony optimization

Because of the distributed control of the network, the dynamic nature of the traffic and the unpredictability of a failure event, the flexibility and robustness of ant colony optimization (ACO) make it a suitable candidate for provisioning lightpaths in an optical network. In this work, we propose a fault-tolerant dynamic routing and wavelength assignment (RWA) algorithm based on the ACO framework, presenting its integration into the Generalized multi-protocol label switching (GMPLS) control plane. By simulating two different scenarios, we demonstrate the effectiveness of this algorithm when a single link or node failure occurs.

A tabu search heuristic for the routing and wavelength assignment problem in multigranular optical networks

This paper proposes a tabu search heuristic for solving the routing and wavelength assignment problem in multigranular optical networks, considering the wavelength-continuity constraint and a set of connections to satisfy. For a number of fibers per link, a number of wavebands per fiber, and a number of wavelengths per waveband, this algorithm attempts to minimize the total number of ports used in the network by efficiently grouping lightpaths into bands and fibers, and switching the whole bands and fibers. The algorithm has been implemented and tested on the NSFNET network, and comparisons have been made with the Balanced Path Routing and Heavy Traffic First (BPHT) algorithm in terms of number of ports. Generally, the results obtained with our tabu search heuristic are better than those provided by this algorithm.

A feedback-based congestion control mechanism for labeled optical burst switched networks

In this article we describe a feedback-based OBS network architecture in which core nodes send messages to source nodes requesting them to reduce their transmission rate on congested links. Within this framework, we introduce a new congestion control mechanism called congestion control with explicit reduction request (CCERQ). Through feedback signals, CCERQ proactively attempts to prevent the network from entering the congestion state. Basic building blocks and performance tradeoffs of CCERQ are the main focus of this article.

A dynamic hop count shifting RWA algorithm for wavelength routed optical networks

In this article, we find that the limiting hop count in a lightpath impacts on the performance of optical networks. Based on this observation, we propose a dynamic hop count shifting (DYHOS) algorithm that limits the hop count of lightpaths dynamically, depending on the traffic load. The proposed algorithm searches an available route, while minimizing the waste of network resources and limiting excessive traffic on the network. Hence, the proposed algorithm increases the network throughput and reduces the blocking probability. Comparing with shortest path routing and adaptive path routing algorithms, we show the performance of the proposed algorithm has the lowest blocking probability influenced by the hop count of lightpaths for a given routing algorithm.

An efficient admission control mechanism for optical burst-switched networks

This article proposes the load-level-based admission control (LLAC) mechanism in order to provide service differentiation for optical burst-switched networks. The LLAC mechanism admits bursts of a given service class according to the network load and a class-associated parameter. Based on this parameter, called load level, the proposed mechanism differentiates the burst blocking probability experienced by each service class. We develop an analytical model for the proposed mechanism and evaluate its performance for different configurations through mathematical analysis. The results show that the load-level-based mechanism reduces the blocking probability of high-priority bursts by two orders of magnitude or more depending on the analyzed scenario. In addition, compared to other similar mechanisms, the load-level-based mechanism effectively differentiates the services in all analyzed configurations, requires less states in optical burst switching (OBS) nodes, and does not suffer from priority inversion.

OSNR model to consider physical layer impairments in transparent optical networks

We propose a model that considers several physical impairments in all-optical networks based on optical signal-to-noise degradation. Our model considers the gain saturation effect and amplified spontaneous emission depletion in optical amplifiers, coherent crosstalk in optical switches, and four-wave mixing in transmission fibers. We apply our model to investigate the impact of different physical impairments on the performance of all-optical networks. The simulation results show the impact of each impairment on network performance in terms of blocking probability as a function of device parameters. We also apply the model as a metric for impairment-constraint routing in all-optical networks. We show that our proposed routing and wavelength assignment algorithm outperforms two common approaches.

Packet loss analysis in optical packet-switched networks with limited deflection routing

We present an approximate analytical method for the evaluation of packet loss probability in synchronous optical packet-switched networks which operate under limited deflection routing with the contention resolution method based on priorities. Packets are lost because they are removed by nodes. They are removed because they experience too many deflections and stay prohibitively long in the network. Such packets have to be removed because they will be ignored by the transmission protocols (like TCP) and because the quality of their optical signal is unacceptable. Presented are results for the network in the topology of the torus of the two-dimensional grid, which operates at a steady state with the uniform load u, . The strength of our analysis is its novel mathematical approach, which is capable of providing very low packet loss probabilities. For the network composed of 100 nodes, we predict the packet loss probability as low as 10⁻⁹ or lower, while simulation provided results only at the order of 10⁻⁶. For a given permissible packet loss probability, our analysis provides the maximal network load and the number of allowed deflections. We verify the analysis with simulation in the cases for which simulation gave results.

A new proportional differentiation scheme based on batch scheduling for optical burst switching networks

Optical burst switching (OBS) is a promising switching paradigm for building the next generation optical internet. The proportional differentiation model is very convenient for network operators to quantitatively adjust the quality differentiation among service classes. To provide proportional differentiated services for OBS networks, a proportional differentiation scheme based on batch scheduling is proposed in this article. The scheme adopts the batch scheduling idea to reserve data channel resources for a batch of data bursts. It helps to decrease burst dropping probability. When some data bursts are unsuccessfully scheduled, a preemption method is used to keep a proportional burst dropping probability among service classes according to the expected burst dropping probability equations given by the proportional differentiation model. The scheme has low computational complexity. Simulation results show that the scheme can provide proportional differentiated services and efficiently decrease the burst dropping probability.

Performance analysis of an improved soft preemptive scheme for unevenly distributed traffic in optical wavelength-division multiplexing networks

In optical wavelength-division multiplexing (WDM) networks, traffic can be unevenly distributed across the network causing inefficient utilization of resources. To solve this problem, an improved soft preemptive (SP) scheme is proposed by considering dynamic resource distribution to deal with the uneven network utilization. A novel unevenly distributed traffic model in cross-time-zone networks is also presented to evaluate the efficiency of the new scheme. Compared with other schemes such as normal shortest path first (SPF) routing and wavelength conversion (WC), the new proposed scheme results demonstrate significantly better performance with respect to the network utilization and overall network blocking probability.

An effective buffering architecture for optical packet switching networks

A novel optical buffering architecture for Optical Packet Switching (OPS) networks is proposed in this article. The architecture which adopts a fiber-sharing mechanism aims at solving the problem of using a large number of fiber delay lines that are used to solve resource contention in the core node in OPS networks. The new architecture employs fewer fiber delay lines compared to other simple architectures, but can achieve the same performance. Simulation results and analysis show that the new architecture can decrease packet loss probability effectively and achieve reasonable performance in average packet delay.

DTN Based Dominating Set Routing for MANET in Heterogeneous Wireless Networking

In mobile communications, effective inter-networking is mandatory in order to support user roaming among various types of wireless networks while maintaining connectivity. In this paper, we propose a super node system architecture to achieve the connectivity over interconnected heterogeneous wireless access networks, which employs the delay-tolerant network (DTN) concept to overcome the problem of potential intermittent connections caused by user roaming and ensures message delivery in the presence of a long disconnection period. By introducing the concept of virtual network topology, we present a new routing technique for mobile ad hoc networks (MANETs) within the system architecture, which redefines the dominating-set based routing for the challenged network environment. A time based methodology is presented to predict the probability of future contacts between node pairs for constructing the virtual network topology. Simulation results demonstrate the effectiveness of the proposed dominating-set based routing scheme under the DTN system architecture.

Virtual topology transition sequence problem on WDM networks with dedicated protection

Wavelength-division multiplexing (WDM) technology has emerged as a promising technology for backbone networks. The set of all-optical communication channels (lightpaths) in the optical layer defines the virtual topology for the upper layer applications. Since the traffic demand of upper layer applications fluctuates from time to time, it is required to reconfigure the underlying virtual topology in the optical layer accordingly. However, the reconfiguration for the virtual topology is reluctantly disruptive to the network since some lightpaths should be torn down and some traffic has to be buffered or rerouted during the reconfiguration process. Therefore, it needs to have an efficient transition method to shift the current virtual topology to the new one so as to minimize the effect of the reconfiguration on the upper layer traffic. In this article, the WDM virtual topology transition sequence problem (WVTTSP) which minimizes the average weighted delay (AWD) is studied. Since the WVTTSP is NP-hard, a heuristic solution model is proposed to solve it. Simulation results show that the proposed least weighted distance first (LWDF) method can find the best result and the time spent by it is less than 4 s for a middle-sized network with 100 links and with 30 wavelengths per link.

Reducing vulnerability of shared-path protection subject to double-link failures in WDM mesh networks

Shared-path protection (SPP) is a capacity- efficient mechanism to provide 100% single-link failure protection in WDM mesh networks. After the first link failure, however, if reconfiguration is unavailable, a second link failure may lead to tremendous service interruption. Vulnerability of a link is the percentage of links that are vulnerable to the arbitrary second link failure after the link failed and network vulnerability is defined as the average vulnerability of links in the network. In this article, we present three policies that can reduce network vulnerability by reducing backup sharing in shared-path protection. The first policy tries to restrict the times of sharing a wavelength-link by connections. The second policy tries to avoid backup sharing on highly vulnerable links. The third policy tries to avoid backup sharing on highly vulnerable wavelength-links. Algorithms to implement these policies based on a similar framework are presented. Numerical results suggest that there is a trade-off between capacity efficiency and network vulnerability in all the three policies. The third policy can deliver a better performance in terms of blocking probability and network vulnerability.

Long-term estimation-based burst control algorithm in OBS networks

By taking advantage of statistical multiplexing gain in the burst level, optical burst switching (OBS) technology enables optical Internet to handle huge volume of data in an efficient manner without requiring optical buffers in the optical domain. However, when congestion builds up in the optical network core, large amount of data might be lost. In this article, we propose an efficient optical burst control algorithm that operates based on the awareness of future burst traffic condition to eliminate the effect of congestion reaction delay. The proposed algorithm takes advantage of multiple statistics to improve the estimation accuracy.Through performance evaluation, it is verified that the proposed algorithm proactively controls inbound burst traffic so that the OBS network can stay in a stable traffic condition while keeping the network throughput high.

Genetic algorithm to design logical topologies in reconfigurable WDM networks

A new method to design logical topologies based on genetic algorithms is presented. Not only does the algorithm determine which nodes should be connected by means of lightpaths with the aim of minimizing congestion, but it also solves the routing and wavelength assignment problem. In this way, the algorithm guarantees that the logical topology obtained can be embedded in the optical network subject to the available set of resources. The algorithm is effective in terms of both congestion and fairness. For instance, when compared with other work, the congestion is significantly reduced (from 20% to 75% depending on the matrix of traffic considered), and the fairness, when evaluated in terms of the Jain index, is generally higher than 0.94. Moreover, the algorithm brings advantages when employed in dynamic scenarios where the logical topology is frequently reconfigured, as it is fast and, in contrast to other algorithms previously proposed, the calculation process can be stopped at any time (if required) in order to give the best virtual topology found up to the moment.