Distributed sub-light-tree based multicast provisioning with shared protection in elastic optical datacenter networks

With the rapid development of cloud computing, video, smart home, and Internet of things (IoT), the bandwidth requirements for communications networks are also greatly increasing. The internet is facing new demands and challenges. Space Division Multiplexing (SDM) is an approach to increase the channel bandwidth capacity to explore potential spectrum resources in the spatial dimension with a multi-core fiber (MCF). Thus, this paper mainly proposes a spectrum-efficiency VON mapping approach with the inter-core crosstalk to reduce the spectrum occupancy and the inter-core crosstalk values in Space Division Multiplexing Elastic Optical Data Center Networks (SDM-EODCNs). Simulation results show that the proposed VON approach can efficiently reduce the spectrum occupancy rate and average inter-core crosstalk.

We consider an elastic all-optical network, where each node is multicast-capable and does not support spectrum conversion. In such a network, for a given set of static multicast demands, we consider distance-adaptive spectrum resource allocation, and aim to optimize multicast routing, modulation, and spectrum assignment with shared protection in a way that minimizes the required spectrum resources for accommodating all multicast sessions. In our design, we provision each multicast demand by a light-tree where spectrum resources are allocated in all links included in the tree. We protect each light-tree from any single link failure in both directions by having a backup path that is link-disjoint to the path from the source to each destination on the primary tree. We reserve spectrum resources in the links that are not in the primary tree but in the backup paths between all source-destination pairs. The reserved spectrum resources can be shared to protect multiple light-trees as long as they do not fail simultaneously. For such a problem, we provide a mixed integer linear programming formulation. We also develop a scalable heuristic algorithm with an attribute that enables it to improve the quality of the results at the cost of longer running times. Numerical results for small problems show that the heuristic algorithm performs close to the optimum. In addition, we use a Markov chain simulation of the network to evaluate the performance of our proposed algorithm in terms of blocking probability in a dynamic environment, which demonstrates a significant improvement over straightforward approaches.

We study the problem of dynamic content replacement in terms of network state variation in elastic optical datacenter networks. A dynamic content replacement scheme is proposed to minimize spectrum consumption, blocking probability and network latency.

Virtualization is becoming a promising method for supporting various emerging applications, and achieving efficient embedding of virtual requests in elastic optical networks (EONs) has become a popular issue in network virtualization research. Meanwhile, multicast request mapping of EONs has become more challenging than that of conventional optical networks. Since the problem of minimizing the embedding cost and redundant transmission in multicast request embedding is NP-hard, we propose an efficient heuristic algorithm, called the virtual optical multicast-tree embedding algorithm based on the node correlation degree (VOME-NCD) to address the problem of low transmission redundancy. When embedding the virtual optical multicast request, it is based on the mapping of the correlation degree of each virtual node. Through extensive simulations, we demonstrate that VOME-NCD outperforms other embedding solutions in terms of the embedding cost, blocking probability, redundancy cost, and router hop count.

An efficient critical protection scheme for intra-domain routing using link characteristics

In this paper, we investigate power-efficient directed preconfigured cycles (p-Cycles) for asymmetric traffic protection in elastic optical networks (EONs) against single link failure. Owing to the advantage of distinguishing traffic amount in two directions, directed p-cycles consume low power by allocating different spectrum slots and modulation formats for each direction. A mixed integer linear programming (MILP) model is formulated to minimize total power consumption, which takes into account directed cycle generation, spectrum allocation, modulation adaptation, and protection capacity. To increase the scalability, the MILP model is decomposed, and a two-step approach is proposed: improved cycle enumeration and a simplified integer linear programming model. Extensive simulations are performed to study the power consumption of p-cycles under different traffic patterns in terms of traffic asymmetry (TASY), anycast ratio (AR), and the number of data centers (DCs). The results strongly demonstrate that directed p-cycles obtain significant power savings for protecting asymmetric traffic in EONs. The power savings rise up to 46.91% and 36.38% compared with undirected p-cycles as the TASY and AR increase, respectively. Moreover, the directed p-cycles achieve valuable power savings (up to 46.1%) with the introduction of DCs while the amount of power savings does not depend on the number of DCs.

In elastic optical networks (EONs), a major obstacle to using the spectrum resources efficiently is the spectrum fragmentation. In the literature, several defragmentation approaches have been presented. For 1+1 path protection, conventional defragmentation approaches consider designated primary and backup paths. This exposes the spectrum to fragmentations induced by the primary lightpaths, which are not to be disturbed in order to achieve hitless defragmentation. This paper proposes a defragmentation scheme using path exchanging in 1+1 path protected EONs. We exchange the path function of the 1+1 protection with the primary toggling to the backup state, while the backup becomes the primary. This allows both lightpaths to be reallocated during the defragmentation process, while they work as backup, offering hitless defragmentation. Considering path exchanging, we define a static spectrum reallocation optimization problem that minimizes the spectrum fragmentation while limiting the number of path exchanging and reallocation operations. We then formulate the problem as an integer linear programming (ILP) problem. We prove that a decision version of the defined static reallocation problem is NP-complete. We present a spectrum defragmentation process for dynamic traffic, and introduce a heuristic algorithm for the case that the ILP problem is not tractable. The simulation results show that the proposed scheme outperforms the conventional one and improves the total admissible traffic up to 10%.

Elastic optical network (EON) is a promising candidate for the next generation optical transport network because of its high spectrum efficiency and flexible spectrum allocation. However, to migrate from today’s dense wavelength division multiplexing (DWDM) network to EON, optical nodes such as reconfigurable optical add/drop multiplexers (ROADMs) should be replaced with the ones with expensive flexi-grid wavelength selective switches (WSSs). Thus, whether and how today’s optical network will be evolved to EON is still under debate. Meanwhile, with the technical maturity of optical super-channels that transmit bit rates at the level of 1 Tb/s, super-channels are expected to dominate the future optical transport network because of their attractiveness of high spectrum efficiency and superior cost effectiveness. In this paper, we propose a new quasi-coarse wavelength division multiplexing (Quasi-CWDM) optical network architecture that is compatible to today’s WDM network in spectrum operation, while still maintaining the flexibility of adaptation between the bit rate and the transparent reach of an optical super-channel, but not requiring expensive flexi-grid WSSs. Specifically, the Quasi-CWDM optical network employs large fixed frequency grids, whose spacing falls between the traditional CWDM and DWDM, e.g., 200 GHz or 400 GHz. To maintain the flexibility between the bit rate and the transparent reach of an optical super-channel, different modulation formats are chosen according to channel physical distances. To minimize network hardware cost and maximize carried user traffic demand, we develop a mixed integer linear programming (MILP) model and a heuristic algorithm that can efficiently groom upper-layer IP traffic onto the optical layer by optical super-channels. We compare the design based on the Quasi-CWDM network to those based on the DWDM network and the advanced EON. It is found that the proposed Quasi-CWDM network has a much lower hardware cost than the other two types of networks, while achieving spectrum efficiency close to EON.

This paper focus on the routing, modulation level and spectrum allocation (RMLSA) problem in the next generation datacentre networks, which own the advantages of both Elastic Optical Networks (EON) and Software Defined Networking (SDN). We proposes an Integer Linear Programming (ILP) model for this problem. Simulation results show the ILP model achieves an outstanding load balancing performance.

Extending light-trail into elastic optical networks for dynamic traffic grooming

We propose and investigate a subtree scheme for all-optical multicast routing, modulation level and spectrum allocation (AOM-RMSA) in elastic optical networks. A multicast request is accommodated by several light-trees and each light-tree covers only a part of the destination set. We assume that all nodes are multicast capable and investigate the subtree scheme over the single light-tree scheme for the AOM-RMSA problem under both static and dynamic traffic scenarios. In the static scenario, we formulate an integer linear programming model to obtain the optimal solution. Then, we propose two time-efficient heuristic algorithms that construct subtrees according to the link-sharing ratio between the paths from source to two distinct destinations. The proposed algorithms improve the spectrum utilization by building subtrees that have smaller tree-spanning size and adopt higher level modulation formats. They have also effectively reduced the blocking probability compared to single light-tree schemes.

Resiliency to link failures in optical networks is becoming increasingly important due to the increasing data rate in the fiber. Path protection schemes attempt to guarantee a backup path for a connection upon a failure in the network, thereby reducing the recovery time for a connection. In this paper, we develop a failure dependent path protection scheme that dynamically assigns a primary path and backup paths, one for each failure that would affect the primary path. A connection established on the primary path will be re-established on its backup path only if a failure in the network affects the connection. We evaluate the performance of our developed protocol and compare with an alternative approach based on sub-graph routing that achieves high network utilization and low blocking probability at the cost of re-establishing connections even if the failure in the network does not affect the primary path of the connection. We observe that up to a factor of eight reduction in the number of reconfiguration scenarios is achieved with less than 10% reduction in effective network utilization and less than 3% reduction in fairness metrics for tolerating any single link failure in NSFNET and ARPA-2 networks. The failure dependent protection approach developed in this paper is also applicable to any general failure scenarios that are modeled as shared risk link group failures.

The light-tree-based optical multicasting (LT-OM) scheme provides a spectrum- and energy-efficient method to accommodate emerging multicast services. Some studies focus on the survivability technologies for LTs against a fixed number of link failures, such as single-link failure. However, a few studies involve failure probability constraints when building LTs. It is worth noting that each link of an LT plays different important roles under failure scenarios. When calculating the failure probability of an LT, the importance of its every link should be considered. We design a link importance incorporated failure probability measuring solution (LIFPMS) for multicast LTs under independent failure model and shared risk link group failure model. Based on the LIFPMS, we put forward the minimum failure probability (MFP) problem for the LT-OM scheme. Heuristic approaches are developed to address the MFP problem in elastic optical networks. Numerical results show that the LIFPMS provides an accurate metric for calculating the failure probability of multicast LTs and enhances the reliability of the LT-OM scheme while accommodating multicast services.

An elastic optical network (EON) plays an important role in transport technology for virtualization of networks. A key aspect of EONs is to establish lightpaths (virtual links) with exactly the amount of spectrum that is needed and with the possibility of grooming, the process of grouping many small traffic flows into larger units, creating a super-lightpath. Grooming eliminates the need for many guard bands between lightpaths and also saves transceivers; however, it often leads to the need to perform optical–electrical–optical conversions to multiple-data-rate optical signals at intermediate nodes. The aim of this paper is to provide a mixed-integer linear programming (MILP) formulation, as well as heuristic and meta-heuristic approaches, for the design of multiple virtual optical networks (VONs) in an elastic optical substrate network with bandwidth-variable lightpaths, modulation format constraints, and virtual elastic regenerator placement. Traffic grooming is allowed inside each VON, and a distance-adaptive modulation format technique is employed to guarantee efficiency in terms of bandwidth for a physical substrate, subject to several virtual topologies. A reduced MILP formulation without grooming capability is also proposed for comparison. The complete MILP formulation jointly solves the virtual topology design, regenerator placement, and grooming problems, as well as the routing, modulation, and spectrum assignment (RMSA) problem. The reduced MILP formulation, heuristics, and meta-heuristic, on the other hand, separate the virtual topology design problem from the RMSA problem. It is shown that the grooming approach can provide good results, since it solves the problem for a complete design when compared to the approach without grooming. Furthermore, heuristic solutions for large networks are proposed, which present good performance (in terms of saving spectrum) for the design with large instances.

This paper focuses on the Routing and Spectrum Allocation (RSA) problem in Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) Elastic Optical Networks (EON) with consideration of transmission impairments. A majority of the literature in EON is based on improving the spectral efficiency and efficient utilization of available spectral resources. However, transmission impairments such as pass-band filter narrowing effect, shot noise and amplified spontaneous emission (ASE) beat noise products due to coherent detection and cross-talk in cross-connect (XC) etc. limit the unconstrained allocation of spectral resources. Thus, these transmission impairments may eventually become a barrier to the continuous resource allocation in EON. In this paper, we introduce a novel RSA technique with the transmission impairments in the coherent optical transport network, which we formulate as Transmission Impairments Aware RSA (TIA-RSA) problem. First, an optimal integer linear programming (ILP) for RSA is presented which minimizes delay-bandwidth product. Thereafter, a heuristic algorithm for large networks is also proposed. Our results indicate that the proposed heuristic algorithm yields close to optimal solution for low running times. We further propose an architecture for optical XC for EON.