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.

Burst-cluster transmission with probabilistic pre-emption for reliable data transfer in high-performance OBS networks

Recently, optical switching and packet processing technologies have been developed and high-performance optical burst switching (OBS) networks are constructed by using these technologies. In high-performance OBS networks, several types of applications such as Grid computing and HDTV can be provided for users according to immediate reservation protocol. Because some applications require that data is transmitted reliably over high-performance OBS networks, it is indispensable to provide reliable data transfer service for high-priority users. Therefore, in this paper, we propose a reliable burst transmission method which can be available for the immediate reservation protocol. In the proposed method, both burst-cluster transmission and probabilistic pre-emption are used at edge and core nodes. By using these methods together, the reliable data transfer and the service differentiation can be provided. We evaluate by simulation the performance of the proposed method in the 14-node NSFNET. Numerical examples show that the proposed method can transmit higher-priority bursts more reliably than the conventional method while not increasing the overall burst loss probability so much. In addition, we investigate effective parameter settings from some simulation results.

Physical impairment aware scheduling in optical burst switched networks

Optical burst switching (OBS) presents itself as a promising technology for bridging the gap between optical wavelength switching and optical packet switching. Increasingly, researchers attempt to incorporate more realistic constraints into the design of OBS networks. Optical signal transmission quality is subject to various types of physical impairment introduced by optical fibers, switching equipment, or other network components. The signal degradation due to physical impairments may be significant enough such that the bit-error rate of received signals is unacceptably high at the destination, rendering the signal not usable. In this paper, based on earlier work, we study the burst scheduling problem in OBS networks, taking into account physical impairment effects. We propose three effective burst scheduling algorithms: (1) a JET based Physical Impairment Constrained Algorithm (JETPIC), (2) an Integrated Physical Impairment Constrained Algorithm (IPIC), and (3) an Enhanced Integrated Physical Impairment Constrained Algorithm (EIPIC). At an OBS node, the proposed algorithms schedule bursts for transmission by searching for available resources as well as verifying signal quality. Our simulation results show that the proposed algorithms are effective in terms of reducing the burst blocking probability. In general, algorithm JETPIC outperforms algorithms IPIC and EIPIC in burst blocking probability and average end-to-end delay performance.

Addressing conversion cascading constraint in OBS networks through proactive routing

The negative impact of cascaded wavelength conversions has been largely ignored in optical burst switching performance evaluations. When optical bursts are transmitted all optically from source to destination, each wavelength conversion performed along the lightpath may cause some signal-to-noise deterioration. If the distortion of the signal quality becomes significant enough, the receiver would not be able to recover the original data. In this paper we examine the performance degradation when an upper bound on the number of wavelength conversions that a signal can go through is enforced. We refer to this constraint as conversion cascading constraint. We propose a novel proactive routing scheme under this constraint that considers the instantaneous link congestion at the moment when the bursts arrive. It has three major advantages: (1) utilize the same offset times for the same node pairs while providing dynamic routing without using any fiber delay lines (FDL); (2) decrease burst loss probability to a great extent; (3) mitigate unfairness among the bursts with different hop counts, which is even worse under the conversion cascading constraint if without any special treatment. We also extend the proposed mechanism to embrace a variant of regulated deflection routing which can further improve network performance.

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 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.

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).

On capacity planning for the GMPLS network control plane

This article presents capacity planning rules for the control plane of all-optical networks featuring GMPLS and RSVP-TE as a connection setup protocol. As per RSVP standard, a refresh message mechanism is incorporated to RSVP such that the state is periodically refreshed on a link per link basis. We provide analytical expressions for the bandwidth and buffer sizes to be provided such that no flows are torn down due to lack of refresh messages. Our findings show that small buffers (several KBytes) suffice to sustain the signaling load for as much as 400 RSVP flows per link, with the simplest RSVP refresh mechanism (neither using link bundling nor acknowledgments). On the other hand, we also find the packet drop probability per link for a given network topology for the case that the flow survival probability is larger than a given threshold. We provide numerical examples based on the COST 239 european network topology and real RSVP traffic traces from early-commercial switching equipment.

Feasibility analysis for service differentiation using an FDL bank in OBS networks

A service differentiation scheme in optical burst switching (OBS) networks, which is based on dynamic fiber delay line (FDL) assignment, is shown. The effectiveness of the scheme is validated by numerical analysis and extensive simulations. Especially, the feasibility conditions for the service differentiation scheme, which are considered as the minimum number of FDLs for each sub-FDL group, are displayed. The feasibility conditions are derived numerically, and are verified through extensive simulations. The results of extensive simulations show that the proposed scheme and the feasibility conditions are valid for service differentiation in OBS networks.

An adaptive load-aware burst assembly scheme to achieve optimal performance of FDL buffers in OBS networks

Optical burst switching (OBS) is regarded as one of the most promising switching technologies for next generation optical networks. Contention resolution of data bursts is a critical mission to implement practical OBS. The use of fiber delay line (FDL) buffers has received a lot of attention as a fundamental but effective solution to resolve burst contention. Several studies have investigated the way to achieve the optimal performance of FDL buffers at a single-node level. However, this article studies how to achieve the best performance of OBS networks with FDL buffers under varying traffic condition at a network level. For this purpose, we propose an adaptive load-aware burst assembly (ALBA) scheme, which adaptively adjusts the size threshold of burst assembler optimized to the current network traffic load. A piggybacking method used to deliver the traffic-load information from core nodes to ingress edge nodes accelerates the adaptiveness of the proposed scheme by reducing the update time of the size threshold. The effectiveness of the ALBA scheme is proved by comparing with No-FDL case and fixed size-threshold cases under changing traffic-load environment from extensive simulation tests.

On the fairness improvement of channel scheduling in optical burst-switched networks

In the past years, several signaling protocols were proposed for OBS networks and the most popular one is the Just-Enough-Time (JET) protocol. JET not only efficiently utilizes the network capacity, but also effectively reduces the end-to-end transmission delay. However, the most critical defect of JET is its intrinsic deficiency: Fairness. The fairness problem is a traditional problem common to various kinds of networks. It results in a phenomenon that bursts with a shorter number of hops are generally favorized and hence deteriorates the network utilization as well. In this article, we investigate this problem and propose a fair channel scheduling algorithm as a solution. Usually there is a tradeoff between fairness and blocking performance. Accordingly, the objective of our scheme is to achieve a balance between the two conflicting metrics as much as possible. In our scheme, each burst is associated with a dynamic priority which is defined by several characteristics of the burst. When contention occurs, the proposed scheme picks the preferable burst and drops the other one according to their priorities. From simulation results, we observed that the proposed scheme could improve fairness without causing significant reduction in dropping performance. Furthermore, it increases the effective link utilization as well.

A frequent-pattern approach for optical networks routing planning

Optical burst switching (OBS) networks have been receiving much attention as a promising approach to build the next generation optical Internet. In the bufferless DWDM switching technology, burst loss that should be minimized is the key design parameter. One of the critical design issues in OBS network is how to plan the optimal routing path in order to minimize burst dropping due to network resource contention. This study proposes the burst frequent-pattern tree (BFP-Tree) approach to pre-determine a suitable routing path in the OBS network. The BFP-Tree approach essentially is a learning-based mechanism that is able to determine a suitable transmission path from the historical network transaction data. The experiment results show that the successful rates of routing paths obtained by the BFP-Tree approach are able to converge to those of the optimal results.

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.

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.

Framework for Analysis of Transmission Rate Scheduling for Wireless CDMA Data Networks

The optimal utilization of network resources and the capacity to fulfill quality of service requirements are key requirements for 3rd G networks operations. Several burst admission and transmission rate scheduling algorithms are proposed in the literature. In this study, we develop an analytical framework for the downlink transmission rate scheduling problem for CDMA networks employing discrete service bit rates. The framework uses the average downlink transmit power as the system state and develops a K-dimensional Markov chain representing all possible states in the system. In addition, the transition probabilities due to arrivals of burst requests are made a function of the power utilization and the average power required to support the new burst taking into account the path loss model. The study assumes a transmission rate assignment scheme where the maximum possible system bit rate is assigned given the current system state and the subscriber’s eligibility profile for particular system service rates. The analytical model provides performance metrics such as system throughput, average power utilization, average number of simultaneous transmissions, burst request blocking probability, and mean burst service time. While the developed model is applicable for a general CDMA based network with arbitrary discrete system service bit rates, the model is evaluated for the example of a cdma2000 1xRTT network. A comparison between simulation and analytic results to assess the accuracy of the model is provided.

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.

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.

A wavelength-buffering scheme for dynamic traffic in optical wavelength-division multiplexing networks

In optical wavelength-division multiplexing (WDM) networks, traffic can be very “bursty” at a fine time scale, even though it may seem to be smooth at coarser scales (e.g., Poisson or Poisson-related traffic). This paper analyzes the instantaneous characterization of Poisson traffic at a fine time scale. The analysis shows that the irregular oscillation of the instantaneous traffic load and the occurrence of blockings in a light-loaded network are highly correlated. Specifically, most blockings occur concentratively at the peaks of the instantaneous load. In some other time, network resources may not be sufficiently utilized. To make better utilization of network resources, a novel wavelength-buffering (WB) scheme is proposed for the first time in this paper. By reserving a portion of resources in a “wavelength buffer” under light loading and releasing them when the load goes up, a number of blockings brought by the oscillation of the traffic load can be avoided. Simulation results show that compared with other schemes such as adaptive routing, wavelength conversion (WC), and rerouting, the novel wavelength-buffering scheme achieves significantly better performance with respect to the network utilization and overall blocking probability.

On burst-header contention-resolution in OBS networks

Advances in enabling technologies and the explosive growth of Internet traffic has led to the widespread proliferation of network systems in recent years. With their relatively low cost, high throughputs, high-bandwidth utilization, and low-transmission latency, Optical Burst Switching (OBS) networks represent an ideal solution for next-generation Internet applications. However, in OBS networks, Burst Header Packet (BHP) contentions occur when two or more BHPs are switched simultaneously to the same output port of a given core node. These contention events result in significant losses of the corresponding data burst. Accordingly, this study presents a Store-and-forward COntention-REsolution mechanism, designated as SCORE, which utilizes fiber delay line buffers to resolve the BHP collision problem, thereby minimizing the burst loss rate. The results of a series of simulations performed using an OIRC OBS-ns simulator confirm the effectiveness and efficiency of the proposed scheme.

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.