Virtual topology mapping in elastic optical networks

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.

A flexible data retrieval service is needed in data center networks, where erasure coding has been widely adopted. Elastic Optical Networks, based on Nyquist wavelength division multiplexing or optical orthogonal frequency division multiplexing is an ideal backbone for data centers, since they can efficiently utilize the optical fiber's bandwidth in an elastic manner by partitioning the bandwidth into hundreds or even thousands of subcarriers. In this paper, we study the erasure-coded data retrieval problem for dynamic traffic in elastic optical networks, the objective is to minimize the blocking ratio. A heuristic based on List Scheduling was proposed. Simulation results show that the blocking ratio is reduced in comparison to a benchmark method.

Virtual optical network mapping and core allocation in elastic optical networks using multi-core fibers

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.

Network virtualization can improve the utilization of a physical network by enabling the coexistence of multiple virtual networks supporting different services. For an elastic optical network, network virtualization would create a number of virtual optical networks (VONs) embedded in the same physical optical network. Conventionally, each of these VONs is allocated with a fixed amount of network resources. However, the traffic demand on a VON is usually dynamic, varying over time. This leads to a mismatch between the fixed resource assigned and the actual resource required by users. Therefore, some user services may be blocked and the quality of service provided by each VON may be degraded. To overcome the disadvantage caused by this mismatch, we propose a network resource-sharing scheme, called spectrum trading (ST), which trades spectrum resources between different VONs based on their actual capacity requirements, for better overall spectrum utilization. Integer linear programming (ILP) models are developed to model the different ST scenarios, and heuristic algorithms are developed to tackle ST in large networks. Simulation studies show that the proposed ST scheme is effective in significantly improving the total traffic demand carried by VONs by up to 20% in the test networks considered, while not bringing in any additional hardware cost.

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.

An Elastic Optical Network (EON) nowadays usually accommodates multiple Virtual Optical Networks (VON) by allocating orthogonal spectrum resources for them. A fixed resource allocation pattern may result in a low quality of service since data traffic on VONs may fluctuate with time. Spectrum trading (ST) among VONs could solve this problem by moving spectrum resources between them and blockchain-based ST has recently gained much interest since it avoids the traditional centralization concern. In this paper, we propose a smart contract based decentralized ST scheme for VONs. The system is built on a private blockchain which can be implemented with the off-shelf Ethereum platform at a low development cost. A frequency slot (FS) trading contract (FSTC) is designed to trade unoccupied spectrum resources among VONs. Compared with existing schemes, FSTC explicitly addresses the virtual link brokerage (VLB) problem by trading in the granularity of virtual links. Furthermore, FSTC ensures FS information authenticity and enables FS recyclability via mechanisms based on Ethereum smart contract features. We implement FSTC with Solidity and evaluate its costs which demonstrate the feasibility of the proposed solution.

Elastic optical networking is attracting much attention as a promising solution to achieve spectrum-efficient transport of higher data rates at 100 Gbits/s and beyond. If we draw an analogy to virtualization in cloud computing, it can be seen as network level resource virtualization of optical networks where spectrum resources in optical links are segmented as shareable resources and adaptively aggregated to create a wide variety of optical channels (OChs). In this paper, we discuss the benefits of introducing virtualization into the optical domain from the viewpoints of the network level and the hardware level. In elastic optical networks, a frequency slot through which an OCh is transported and the OCh itself are explicitly decoupled. While the adaptability in the frequency slot is brought about by bandwidth variable wavelength-selective switches, the adaptability in an OCh is yielded by digital coherent technology that is employed in transponders and regenerators. It is emphasized that in order to achieve transponders and regenerators that accommodate heterogeneous traffic demands in an economical manner, simply being adaptive is not enough, and being shareable is essential. We refer to this concept as hardware level virtualization. As examples, we describe a multiflow transponder and an elastic regenerator with results that show proof of concept. Based on the hardware virtualization concept, we propose an elastic optical transport system (EOTS) architecture that enables cost- and energy-efficient IP traffic offloading to the optical domain and improves programmability and automation of optical networks.

Routing, modulation and spectrum allocation of dynamic anycast based on ant colony optimization in elastic optical networks

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

Extreme-scale science applications are highly innovative and constantly evolving. They are expected to generate data in the petabyte and exabyte ranges. This data needs to be transferred, processed, and analyzed at remote locations. A flexible data retrieval service is needed, where a user requesting data retrieval from a remote site can have a choice between replicated storage sites. Elastic Optical Networks are ideal backbone networks, since they can efficiently utilize the optical fiber's bandwidth in an elastic manner by partitioning the bandwidth into hundreds or even thousands of subcarriers. In this paper, multi-sourced data retrieval problem, called reverse manycast, is studied for static traffic in elastic optical networks, the objective is to minimize the total transmission completion time of all the requests. A novel ILP formulation and a low-complexity heuristic are proposed. Simulation results are presented to demonstrate that the proposed method can save up to 37% in completion time compared with a benchmark.

A novel method to implement multiple optical virtual private networks (OVPNs) over an existing WDM passive optical network is proposed. The feasibility of ring-shaped 10 Gbit/s OVPNs is experimentally demonstrated.

In the software defined optical network (SDON) for virtual network services, there still exists unbalanced traffic load distribution in SDON. The traditional load balance mapping method exists in the problem of heavy load of key nodes in optical network and low request acceptance rate of virtual network. In this paper, a virtual mapping method of optical network based on topology awareness is proposed. When the controller of optical network is defined by software, the topology information of nodes and links in the whole network is acquired, and the relative balance weight of each node and link is calculated by combining the connectivity factor. When the virtual network service arrives, the optical network is based on the bandwidth of virtual network service the method of node mapping and link mapping is needed to improve the success rate and balance of virtual network mapping, and avoid the local overload of optical network resources.

Network Function Virtualization (NFV) allows multiple Virtual Networks (VNs) to share the underlying physical infrastructure via VN mapping, thus improving the utilization of physical resources. In this paper, for the first time, we study the multicast service-oriented VN mapping that can support big data applications over Elastic Optical Networks (EONs). Since the problem of minimizing the spectrum consumption in multicast service-oriented VN mapping is NP-hard, we propose an efficient heuristic algorithm, called Integrated Genetic and Simulated Annealing (IGSA) algorithm to address the problem with low computational complexity. By encoding node mapping, multicast tree construction, link mapping and spectrum requirements in the same gene and auto-adjusted evolution, and utilizing simulated annealing to find the fittest multicast requests mapping order, IGSA can perform joint optimization for all the multicast requests in a global way. Through extensive simulations, we demonstrate that IGSA outperforms the other heuristic solutions in terms of spectrum consumption, blocking probability and normalized throughput, while achieving close to minimum spectrum consumption with a much lower time complexity than MILP.

Optical networks are crucial to support increasingly demanding cloud services. Delivering the requested quality of services (in particular latency) is key to successfully provisioning end-to-end services in clouds. Therefore, as for traditional optical network services, it is of utter importance to guarantee that clouds are resilient to any failure of either network infrastructure (links and/or nodes) or data centers. A crucial concept in establishing cloud services is that of network virtualization: the physical infrastructure is logically partitioned in separate virtual networks. To guarantee end-to-end resilience for cloud services in such a set-up, we need to simultaneously route the services and map the virtual network, in such a way that an alternate routing in case of physical resource failures is always available. Note that combined control of the network and data center resources is exploited, and the anycast routing concept applies: we can choose the data center to provide server resources requested by the customer to optimize resource usage and/or resiliency. This paper investigates the design of scalable optimization models to perform the virtual network mapping resiliently. We compare various resilience options, and analyze their compromise between bandwidth requirements and resiliency quality.