Fit Spectrum Allocation Research Articles

Center fit spectrum allocation policy for time-varying traffic in survivable elastic optical networks

The bandwidth required of time-varying traffic changes with time. How to allocate bandwidth and choose survivable transmission lightpath for time-varying traffic poses a great challenge to the performance of elastic optical networks. In this paper, a survivable time-varying traffic spectrum allocation based on center fit spectrum allocation with quasi-center spectrum expansion/contraction (STTSA-CFSA-QCSEC) algorithm is proposed for time-varying traffic in survivable elastic optical networks. Specifically, we focus on how to allocate varying bandwidth for time varying traffic in a survivable elastic optical network. Considering the characteristics of time-varying traffic and the direction of bandwidth variation for time-varying traffic, we propose a spectrum allocation policy different from that of traditional fixed-bandwidth requests. At the same time, for reducing the overhead of protecting bandwidth, a survivable single/dual lightpath hybrid policy is designed. Simulation results show that the proposed algorithm can effectively reduce the bandwidth blocking probability and improve spectrum utilization of elastic optical networks.

Dispersion aware first random fit spectrum allocation approach in elastic optical network (EON)

Abstract Elastic Optical Network (EON) is gaining a lot of attention these days because of its capability to dynamically utilize the network resources. It is possible to alter data rates in accordance with the required application by adjusting a number of spectrum slots which enhances spectral efficiency. However, it is difficult for new requests to access the usage of spectrum resources during the entire process especially when the spectrum is split into a number of small segments. Another key challenge in EON is to achieve effective routing and spectrum allocation. This entails looking for a specified route and identifying contiguous aligned spectrum slots for allocation to various requests. In this way, EON aims maximizing the connection while using the least amount of available spectrum resources. With this in mind, this research developed a first random fit (FRF) spectrum allocation technique that takes into account dispersion, which is a major physical flaw in optical networks. This scheme includes the effect of dispersion for the spectrum allocation approach. Using a FRF approach, this scheme tends to allocate a greater number of connection requests and spectrum is utilized in more efficient way. Starting with the lowest indexed slot, this scheme uses the First Fit algorithm and the less stable modulation technique like BPSK to search for and assign the spectrum slot. A random fit assignment strategy is used with a more robust modulation technique (QPSK) to exploit the next higher indexed spectrum slot which suffers larger dispersion effect. Longer light path requests are assigned to lower indexed spectrum slot (lower dispersion slots) using BPSK modulation technique, while shorter light path requests are sent to next higher indexed spectrum slot (greater dispersion slots) using QPSK modulation technique capturing the dispersion sensitive technique. The results show that the proposed technique achieves a minimal bandwidth blocking probability (BBP) of 0.048, Eye opening Penalty (EOP) of 45.45 dB and Quality Factor of 3.889 and B.P compared with other First Fit (FF) and Random Fit (RF) spectrum allocation schemes.

The Effectual Spectrum Defragmentation Algorithm with Holding Time Sensitivity in Elastic Optical Network (EON)

The elastic optical network (EON) fulfills the upcoming generation network requirements such as high-definition videos, high bandwidth demand services, and ultra-high-definition televisions. The key issues in EON are routing spectrum assignment and spectrum fragmentation for spectrum allocation. The spectrum fragmentation issues are resultant in poor consumption of spectrum resources and an increase in the new connection blocking. A flexible defragmentation algorithm must utilize more spectrum resources with a high transmission rate. This paper presents a new multiconstrained defragmentation algorithm (MCDFA) for elastic optical networks. The MCDFA addressed two key issues: spectrum allocation for new connections and then reconfiguring the existing connections in a nondisruptive manner. The first-last-exact fit spectrum allocation policy assigns the spectrum slots during the new connection request. It splits each light path request by disjoint/ nondisjoint and by efficiently handling the small fragmented slots in spectrum resources. The simulation results are evaluated using standard metrics such as bandwidth blocking probability, bandwidth fragmentation ratio, and spectrum utilization gain. The results also demonstrated that our proposed algorithm generates promised solution to EON’s routing, spectrum assessment, and fragmentation issues.

Online routing, distance-adaptive modulation, and spectrum allocation for dynamic traffic in elastic optical networks

Abstract In this work, an adaptive routing, modulation, and spectrum allocation (RMSA) scheme is proposed for dynamic traffic in elastic optical networks (EON) which allocates resources based on EON characteristics during the RMSA decision process. The proposed scheme selects a route from the set of available paths which efficiently utilizes available resources on all links during network operation stage. Initially, routes are determined from the set of available paths based on a feasible modulation scheme with higher data rates and requiring minimum contiguous frequency slots (FSs) as well as satisfying optical reach of the modulated signal. During the operation stage, routes between end pairs are determined from these preselected paths based on maximum idle FSs on a path. This increases resources utilization on the underutilized routes with maximum path contiguity and having minimum fragmentation. In case of tie among routes with similar numbers of maximum idle FSs, the proposed algorithm selects a path with minimum numbers of hops. Finally, the proposed routing algorithm is integrated with the proposed first-last-mixed fit spectrum allocation scheme which increases average path contiguity and reduces average path external fragmentation for connection requests with mixed line rates requiring contiguous FSs. Simulation results show that the proposed RMSA scheme efficiently reduces the amount of blocking probability, reduces average path external fragmentation, increases average resources utilization, and increases average path contiguity in different network scenarios compared to the existing minimum hop based routing and k-distance adaptive paths (KDAP) routing schemes.

Performance of Spectrum Allocation Strategies under the Worst Case Crosstalk Estimation method in SDM-EONs

Present work considers Space Division Multiplexing (SDM) Elastic Optical Networks (EONs) with Multi core fiber (MCF), in which light paths are established on multiple cores. The problem of inter core crosstalk occurs when the adjacent cores use the same spectral portion. Due to the crosstalk in the adjacent cores, the transmission reach which a modulation format can support is reduced, thus affecting the spectral efficiency of the networks. A commonly used method for the crosstalk calculation is the worst case crosstalk estimation method. This method is widely used due to its simplicity. However, the performance of applied spectrum allocation strategies varies under the consideration of this method. Thus, the aim of this paper is to evaluate the performance of the spectrum allocation strategies under the worst case crosstalk estimation method in SDM-EONs with MCF. We apply first fit and first last fit spectrum allocation strategies in this work.

Path-Based Fragmentation Metric and RSA Algorithms for Elastic Optical Networks

Flexi-grid technology has emerged as the evolution of fixed-grid DWDM core optical networks, enabling more efficient utilization of spectral resources and leading to higher overall network throughput. However, it suffers from an aggravated form of the spectrum fragmentation problem that affects fixed-grid networks. This work presents a novel path-based metric to better evaluate the fragmentation of spectral resources in flexi-grid optical networks, which considers that not all links of a path may contain enough free frequency slots and the likelihood that an end-to-end spectral void is large enough to house a connection. Furthermore, two families of heuristic routing and spectrum allocation (RSA) algorithms that preventively attempt to minimize the value of an input fragmentation metric are presented. These are used to evaluate the effectiveness of multiple metrics, both introduced in this work and from the existing literature, via simulations. We find that both proposed families can perform better, in terms of blocking probability and achievable network throughput, than the well-known K-shortest paths routing with a first fit spectrum allocation policy, with one of them trading performance for lower complexity, and that the proposed fragmentation metric outperforms the existing ones.

A Performance Comparison of Centralized and Distributed Spectrum Management Techniques in Elastic Optical Networks

Elastic optical networks (EONs) have emerged to provide higher spectrum efficiency than traditional Dense Wavelength-Division-Multiplexing (DWDM) by utilizing enabling technologies such as flexible spectrum grid, Orthogonal Frequency Division Multiplexing (OFDM), and distance adaptive rate and modulation. The choice of the control-plane is an important consideration when deploying any new technology, especially in optical networks. This paper considers generic distributed and centralized spectrum assignment policies in conjunction with the accompanying connection set-up signaling protocols in EONs. A network simulator for Generalized Multiprotocol Label Switching (GMPLS) was developed with Forward Reservation Protocol and Backward Reservation Protocol signaling methods. These signaling techniques are used with the First Fit (FF) and Random Fit (RF) Routing and Spectrum Allocation (RSA) algorithms. The paper discusses control elements (central and distributed architectures) decisions under busy hour and normal network conditions and presents a comprehensive performance analysis of key performance metrics such as connection success rate, connection establishment time, and capacity requirement.

Dispersion Based Highest-Modulation-First Last-Fit Spectrum Allocation Scheme for Elastic Optical Networks

This paper proposes a spectrum allocation scheme based on highest modulation-first last fit (LF) for elastic optical networks in order to suppress the call blocking in the network. The proposed scheme searches the available spectrum slots from the highest indexed spectrum slots and selects the slot position with the modulation level as high as possible, which guarantees the least spectrum slots consumption. It provides higher preference of the less robust modulation technique in order to minimize the number of required slots. The last fit spectrum allocation policy is used to keep lower indexed position slots available as much as possible, which have less dispersion effect, for incoming lightpath requests and gives them the opportunity to use the less number of slots. We introduce a dispersion-based highest modulation-first LF algorithm for allocation lightpath requests. The numerical results indicate that the proposed scheme outperforms the conventional schemes in terms of blocking probability, modulation usage ratio, and average number of required spectrum slots.

Spectrum Allocation Policy in Elastic Optical Networks

Abstract The considered problem covers routing and spectrum allocation problem (RSA problem) in Elastic Optical Networks while maintaining the spectrum continuity constraints, non-overlapping spectra constraints for adjacent connections on individual links of the network and spectrum contiguity constraints of the connection. In this article the modified version of the First Fit spectrum slot allocation policy for Fixed Alternate Routing in flexible optical networks has been proposed. The Fixed Alternate Routing with proposed spectrum allocation policy rejects fewer requests, provides less bandwidth blocking probability and less spectrum fragmentation than Fixed Alternate Routing with well-known First Fit and Exact Fit spectrum allocation policies. However, the cost of improving these parameters is a higher computational complexity of the proposed allocation policy.

Dispersion-Adaptive First–Last Fit Spectrum Allocation Scheme for Elastic Optical Networks

The quality-of-transmission (QoT) degradation due to the dispersion effect in longer lightpaths is higher than that of shorter lightpaths in a dispersion uncompensated network. To overcome this shortcoming, this letter proposes a dispersion-adaptive first–last fit spectrum allocation scheme for elastic optical networks to decrease the call blocking in the network. The proposed scheme assigns longer lightpath requests from the smallest indexed spectrum slot, where the dispersion effect is less, and shorter lightpath requests from the largest indexed spectrum slot, where the dispersion effect is more. As a result, a less robust modulation technique is used to maintain the QoT threshold level for the longer lightpath requests, and hence a lower number of spectrum slots are required for lightpath establishment. Simulation results show that the proposed scheme outperforms the conventional scheme in terms of blocking probability and contiguous aligned available slot ratio.

A subcarrier-slot partition scheme with first-last fit spectrum allocation for elastic optical networks

Bandwidth fragmentation refers to the existence of non-aligned and non-contiguous available subcarrier slots in elastic optical networks. Since spectrum for a connection must be allocated to contiguous slots and aligned along the routing path, non-contiguous and non-aligned available slots could cause call blocking. This paper proposes a subcarrier-slot partition scheme with first-last fit spectrum allocation for elastic optical networks in order to increase the number of contiguous aligned available slots, and hence the blocking probability in the network is suppressed. The partition approach creates more aligned available slots by separating the spectrum allocation of the non-disjoint connections. The first-last fit allocation policy creates more contiguous aligned available slots between two partitions. Simulation results show that the partition approach with first-last fit allocation policy provides lower blocking probability than that of the non-partition approach and the partition approach with other spectrum allocation policies. Furthermore, simulation results indicate that the blocking probability in the network using the proposed scheme improves as the number of partitions is reduced.

Class-based first-fit spectrum allocation with fragmentation avoidance for dynamic flexgrid optical networks

A novel Class-Based First Fit (CBFF) spectrum allocation policy is proposed for dynamic flexgrid optical networks. The effectiveness of the proposed CBFF policy is compared with that of the First Fit (FF) policy for single-link and network scenarios. Throughput is shown to be consistently improved under the proposed CBFF policy with throughput gains of up to 15%, compared with the FF policy for the network scenarios we studied. The reduction in bandwidth blocking probability with CBFF with respect to FF increases as the link capacities increase. Throughput gains of CBFF compared with those of FF are more significant under alternate routing as opposed to fixed routing.