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.

A connectivity-based approach for the construction of hierarchical WDM network topology

A hierarchical network model can effectively reduce the complexity of routing and wavelength assignment (RWA) in wavelength division multiplexing (WDM) networks compared to a flat model. However, the resource utilization may greatly suffer if the hierarchical architecture is not properly arranged. By considering the degree of each WDM node and the location effect, this paper proposes a systematic approach to construct the hierarchical topology in WDM networks so that resource utilization can be maximized. Simulation results demonstrate that the performance of the proposed scheme is superior to that of another scheme.

Providing differentiated services for multi-class traffic in IP/MPLS over WDM networks

Providing differentiated services in IP/MPLS over WDM networks has attracted a lot of recent attention. This article extends the Path Inflation Control (PIC) policy recently proposed by us to provide differentiated services in IP/MPLS over WDM networks with traffic grooming. Three different algorithms are considered for provisioning differentiated services. The simulation results show that, with two of the three algorithms, the network cannot only provide differentiated services when the traffic load is high but also gives significantly lower blocking for the lower priority class traffic and for the overall traffic at low traffic loads.

Genetic evolutionary algorithm for optimal allocation of wavelength converters in WDM optical networks

In this article, a genetic evolutionary algorithm is proposed for efficient allocation of wavelength converters in WDM optical networks. Since wavelength converters are expensive, it is desirable that each node in WDM optical networks uses a minimum number of wavelength converters to achieve a near-ideal performance. The searching capability of genetic evolutionary algorithm has been exploited for this purpose. The distinguished feature of the proposed approach lies in handling the conflicting circumstances during allocation of wavelength converters considering various practical aspects (e.g., spatial problem, connectivity of a node with other nodes) rather than arbitrarily to possibly improve the overall blocking performance of WDM optical networks. The proposed algorithm is compared with a previous approach to establish its effectiveness and the results demonstrate the ability of the proposed algorithm to efficiently solve the problem of Optimal Wavelength Converters Allocation (OWCA) in practical WDM optical networks.

Partheno genetic algorithm for dynamic multi-services restoration in WDM networks

Dynamic restoration algorithms which support real-time and multi-services recovery are significant for the survivability of WDM (wavelength division multiplexed) networks. In this article, an intelligent dynamic restoration algorithm for multi-services in WDM networks based on the partheno genetic algorithm is proposed. In these networks, partial wavelength conversion is used. The algorithm is implemented within an interconnected multilayer-graph model and two kinds of optical networks matrix models. Compared with the basic restoration scheme, the proposed algorithm can make use of available network state information and can restore the affected multi-services fast and parallel. Simulation showed that the proposed algorithm can improve the restoration efficiency under high loads and reduce the service disruption ratio on the basis of fully utilizing resources of the network.

On the performance of distributed lightpath provisioning with dynamic routing and wavelength assignment

Distributed lightpath provisioning in wavelength-division multiplexing (WDM) networks has gained wide research interests. In this article, we study the performance of distributed lightpath provisioning in WDM networks with dynamic routing and wavelength assignment (RWA). Specifically, we consider the case where routing of each lightpath is calculated based on globally flooded link-state information, and wavelength assignment is decided through local information exchanges. Simulation results show that such schemes steadily outperform those schemes with only global flooding or only local information exchanges. More significantly, the impacts of various factors on the proposed scheme, including RWA algorithm, network topology, number of wavelengths per fiber, global flooding interval, and traffic load, have been evaluated. Such evaluations help to achieve some insights useful for the future developments of efficient lightpath provisioning schemes.

Sparse traffic grooming in WDM networks using coarse granularity OXCs

Providing grooming capability to optical crossconnects (OXCs) in wavelength division multiplexing (WDM) networks can allow an effective use of the network bandwidth, however, it increases the node cost that operators must sustain when compared to a non-grooming network. Therefore, operators might consider using sparse grooming instead of full grooming networks. In this article we consider sparse groomed optical networks. Our contribution is 2-fold. First, we address the grooming placement problem that seeks for a set of grooming nodes in the network that leads to the highest overall throughput. This problem is separated into two sub-problems: (i) selection of nodes having grooming capability; (ii) maximization of network throughput assuming the grooming nodes found by the previous step. These two sub-problems are mathematically formulated for different OXC placing strategies considering a static traffic scenario. In the second part, we design a practical heuristic grooming algorithm suitable for dynamic traffic scenarios. The benefit of using sparse grooming nodes, when compared with a non-grooming scenario, is evaluated in terms of throughput and optical port utilization. Our analysis differs of previous ones since it considers grooming at a granularity coarser than the traffic granularity, which is an important aspect since network cost improvement can be obtained at the expense of irrelevant performance impairments. Results show that the insertion of coarse granularity OXCs can be a viable solution for network throughput increase since this can be done at the expense of relatively few or no extra optical ports.

Coordination of wavelength and time-window assignment in WDM-based TDM hybrid-PONs

In passive optical networks (PONs), the low effectiveness in terms of service utilization and network evolution have been important design issues. In this article, we introduce a hybrid access network architecture, so called scalable WDM-based Ethernet hybrid-PON (SWE-PON), which features a wavelength-division-multiplexed (WDM) feeder network using a combination of tunable laser device (TLD) and cyclic arrayed waveguide grating (AWG) and time-division-multiplexed (TDM) distribution network based on a reflective transmission mode. Necessary conditions needed to guarantee flawless packet transmission through normal WDM/TDM hierarchical PONs including the SWE-PON, are analyzed. We also propose a hierarchical fair time-window allocation mechanism which coordinates wavelength assignment and time-window bandwidth allocation so that high link utilization and fair bandwidth allocation are guaranteed in every multiplexing level.

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.

A new lightpath establishing method for dynamic traffic grooming under the overlay model

This paper proposes the use of the saturated cut (SC) method to improve the network performance through efficient dynamic traffic grooming in IP/MPLS over WDM networks using an overlay model. With the SC information from the IP/MPLS layer, the optical layer can calculate a lightpath between two node sets rather than the earlier suggested approach of calculating such paths just between two nodes for better performance. We have used two criteria, bandwidth and path length, to find SCs and have proposed two algorithms which incorporate this in the path inflation control (PIC) policy proposed earlier. Two typical networks, NSF and COST239, were used for examining the network performance. The simulation results show that though both methods can significantly improve the overall network performance the SC method is more efficient for a sparse network like the NSF network rather than for a dense network like the COST239 network. Since calculating lightpaths for all node pairs for a SC is time consuming, we propose a considerably simpler heuristic approach that can provide almost the same level of performance improvement as the SC method but with much lower complexity.

Multiobjective evolutionary approach to cost-effective traffic grooming in unidirectional SONET/WDM rings

Traffic grooming in optical networks is the process of multiplexing and demultiplexing low-speed traffic streams onto high-speed wavelengths. The research in the domain of traffic grooming mainly focuses on minimizing number of SONET add/drop multiplexers (SADMs) in SONET/WDM rings and it has been shown that they can potentially be reduced by careful assignment of low-speed traffic streams onto high-speed wavelengths. However, the cost of the network not only depends on the number of SADMs, but also the number of wavelengths and the grooming ratio. It is often the case that all of them cannot be minimized simultaneously. In this article, the problem of minimization of cost of a SONET/WDM unidirectional ring has been modeled as a multiobjective optimization problem which simultaneously minimizes the number of SADMs, the number of wavelengths, and the grooming ratio. A popular multiobjective genetic algorithm (NSGA-II) has been used as the underlying optimization tool. The resultant set of near-Pareto-optimal solutions contains a number of nondominated solutions, which the user can judge relatively and pick up the most promising one according to the problem requirements. Performance of the proposed algorithm has been demonstrated on different network topologies.

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.

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.

Solving virtual topology reconfiguration problem on survivable WDM networks by using simulated annealing and genetic algorithms

In a Wavelength Division Multiplexing (WDM) network, the performance of the virtual topology (VT) designed for a pre-specified traffic pattern can be improved by performing virtual topology reconfiguration (VTR). Simultaneously, the provision of survivability of WDM networks is important, because the transmission of huge data should be protected when a fiber fails. Thus, the combination of survivability and reconfiguration is an important issue in WDM networks. In this paper, the Virtual Topology Reconfiguration Problem (VTRP) in survivable WDM networks with a reconfiguration constraint is studied. Given the physical topology, dedicated path-protection VT, and a new traffic demand matrix, the goal of VTRP is to reconfigure the current VT under the pre-specified reconfiguration constraint so that the objective value can be minimized. The object cost of VTRP is the average weighted propagation delay (AWPD). Because designing a polynomial time algorithm to find the optimal solution of VTRP is impractical, in this paper, a simulated annealing (SA) algorithm and a genetic algorithm (GA) are proposed to solve this problem. Experimental results of these algorithms are also given.

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.

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.

Fault-tolerant architecture with dynamic wavelength and bandwidth allocation scheme in WDM-EPON

This study proposes a novel cost-based fault-tolerant WDM-EPON (CFT-WDM-EPON) to provide overall protection. It only equips a backup feeder fiber to recover the system failure. Additionally, a prediction-based fair wavelength and bandwidth allocation (PFWBA) scheme is proposed to enhance the differentiated services for WDM-EPON based on dynamic wavelength allocation (DWA) and prediction-based fair excessive bandwidth reallocation (PFEBR) from our previous work. PFEBR involves an early-DBA mechanism, which improves prediction accuracy by delaying report messages of unstable traffic optical network units (ONUs), and assigns linear estimation credit to predict the arrival of traffic during waiting time. DWA can operate in coordination with an unstable degree list to allocate the available time of wavelength precisely. Simulation results show that the proposed PFWBA scheme outperforms WDM IPACT-ST and DWBA3 in terms of packet delay, jitter performance, throughput, wasted bandwidth, gain ratio of bandwidth, and packet loss.

Reducing the lightpath establishing time of FWM-aware dynamic RWA for wavelength-routed optical networks

A dynamic routing and wavelength allocation technique with an interplay between physical and network layer parameters encompassing Four-wave mixing (FWM) awareness and teletraffic performance of wavelength-routed optical networks has previously been proposed for a distributed approach. In this article, we present a fast computational algorithm for our routing and wavelength assignment (RWA) encompassing FWM-induced crosstalk. The objective is to minimize the time of establishing a dynamic lightpath. For this purpose, a precomputed matrix of FWM crosstalk products is used in an adapted version of the FWM-aware dynamic RWA algorithm. The approach is validated through simulations showing improvement up to 30–50% on the provisioning time of lightpaths for different network topologies compared to an online full computational scheme.

A New efficient dynamic MAC protocol for the delivery of multiple services over GPON

The Gigabit-capable passive optical network (GPON) has become an attractive and promising solution for the broadband access network. It is apparent that an efficient medium access control (MAC) protocol is crucial not only to catalyze the utilization of the upstream resources but also to support the GPON encapsulation method (GEM) for multiple services over GPON. A new approach for bandwidth reporting is developed to achieve dynamic awareness of both the changes of ONU queue status and the consequences of previous allocations. In addition, a novel balance transferring mechanism that enables a register and transfer process for successive allocation across multiple frames is presented. By incorporating the new schemes of bandwidth reporting process and the balance transferring mechanism into a frame-based scheduling procedure, an efficient dynamic bandwidth assignment MAC protocol is developed to support differentiated services over GPON. The performance of the new protocol is simulated and evaluated under a variety of traffic distributions. Simulated characteristics demonstrate a significantly improved network performance.