Wavelength conversion in future WDM optical transport networks

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.

Content caching is an effective technique that reduces network power consumption by reducing the path between users and requested video content. This paper examines the benefit of caching in an IP over WDM core network with respect to current and future networks. It compares the power savings due to caching in current implementations of optical networks to potential power savings when future optical network features are realized. Future optical core networks are considered with three major power efficiency improvements over current networks. First, network devices are equipped with sleep-mode capabilities where inactive parts of storage devices are put in low-power mode. Second, optical bypass is employed where intermediate IP routers are not engaged in traffic routing. Third, the power consumption of router ports is significantly reduced, consequently reducing the power consumption of transport. The results show that content caching is effective in reducing power consumption under both current and future optical networks, making caching a successful option for video delivery in the future Internet.

In future optical networks, versatile functionalities will be required for the optical network subsystems to fully utilize the spectral resources with low energy consumption. The key technologies are the spectral efficient MUX/DEMUX technique and flexible control of optical channels with high frequency granularity. An orthogonal frequency division multiplexing (OFDM) and Nyquist wavelength division multiplexing (N-WDM) are the most promising candidates of spectral efficient multiplexing techniques, and all-optical (AO) processing is expected to reduce the energy consumption. In an AO-OFDM systems, discrete Fourier transform (DFT) and inverse DFT (IDFT) are performed in optical domain by specially designed arrayed waveguide gratings (AWGs). In our experiment, 12.5 GHz spaced AO-OFDM system has been successfully demonstrated with no guard interval. In N-WDM systems, the Nyquist signal is generated by using carrier-suppressed return-to-zero (CS-RZ) signal and optical Nyquist filtering, which is achieved with two flat-top AWGs and optical interleaver, and the 25 Gbaud signals are successfully multiplexed in the experiment. Although both AO-OFDM and N-WDM can achieve the highest spectral efficiency, N-WDM is more suitable for flexible optical networks. This is because the N-WDM channels have less spectral overlap with the other channels than AO-OFDM, owing to its rectangular shaped compact spectrum. Therefore, N-WDM channel can be easily multiplexed and demultiplexed by optical filters. At an optical network node, channel defragmentation is indispensable technology to flexibly control the optical channels. We have experimentally demonstrated a format independent optical channel defragmentation with N-WDM signal. We believe these technologies are promising for future flexible optical networks.

In this paper, we propose a new ant-based algorithm for the dynamic routing and wavelength assignment (RWA) problem in optical WDM networks under the wavelength continuity constraint. Unlike conventional approaches, which usually require centralized global network information, our new RWA algorithm constructs the routing solution in a distributed manner by means of cooperative ants. To facilitate the ants’ foraging task, we adopt in our algorithm a probabilistic routing table structure for route selection. The new algorithm is highly adaptive in that it always keeps a suitable number of ants in the network to cooperatively explore the network states and continuously update the routing tables, so that the route for a connection request can be determined promptly by the current states of routing tables with only a small setup delay. Some new schemes for path scoring and path searching are also proposed to enhance the performance of our ant-based algorithm. Extensive simulation results upon three typical network topologies indicate that the proposed algorithm has a very good adaptability to traffic variations and it outperforms both the fixed routing algorithm and the promising fixed–alternate routing algorithm in terms of blocking probability. The ability to guarantee both a low blocking probability and a small setup delay makes the new ant-based routing algorithm very attractive for both the optical circuit switching networks and future optical burst switching networks

The traffic carried by core optical networks grows at a steady but remarkable pace of 30-40% year-over-year. Optical transmissions and networking advancements continue to satisfy the traffic requirements by delivering the content over the network infrastructure in a cost and energy efficient manner. Such core optical networks serve the information traffic demands in a dynamic way, in response to requirements for shifting of traffics demands, both temporally (day/night) and spatially (business district/residential). However as we are approaching fundamental spectral efficiency limits of singlemode fibers, the scientific community is pursuing recently the development of an innovative, all-optical network architecture introducing the spatial degree of freedom when designing/operating future transport networks. Spacedivision- multiplexing through the use of bundled single mode fibers, and/or multi-core fibers and/or few-mode fibers can offer up to 100-fold capacity increase in future optical networks. The EU INSPACE project is working on the development of a complete spatial-spectral flexible optical networking solution, offering the network ultra-high capacity, flexibility and energy efficiency required to meet the challenges of delivering exponentially growing traffic demands in the internet over the next twenty years. In this paper we will present the motivation and main research activities of the INSPACE consortium towards the realization of the overall project solution.

Network virtualization over WDM and flexible-grid optical networks

In this paper we deal with online broadcasting and multicasting in a WDM optical network with shared light splitter bank. Our objective is to maximize the network throughput. Since light splitting and wavelength conversion switching in WDM optical networks is cost expensive and fabrication difficult, we assume that only a fraction of network nodes are equipped with limited number of light splitting and/or wavelength conversion switches, and they are shared by all incoming and outgoing signals at each installed node. We first propose two cost models of realizing a broadcast or multicast request to model the consumption of network resources, particularly in modelling the light splitting and/or wavelength conversion resources consumption. We then show that under either of the two proposed cost models, finding a cost-optimal broadcast or multicast tree for a broadcast or multicast request is NP-complete, and instead devise approximation and heuristic algorithms for it. We finally conduct experiments to evaluate the performance of the proposed algorithms.

Optical Networks are considered as the future of broadband communications. One of the popular solutions for wide area networks is Wavelength Division Multiplexing. Wavelength Converters are now a necessity for Wavelength Division Multiplexing Network, but at the same time their cost is a very important factor to consider in network design. It is required that allocated Wavelength Converters should be utilized as much as possible. In this work, Adaptive form of Genetic Algorithm has been applied to utilize maximally the allocation of Wavelength Converters in the optimal manner over the selective nodes available in network. To estimate the fitness, Utilization matrix has been employed. Adaptive in crossover probability and mutation probability have been applied, which are based on current fitness for selected members in crossover and mutation operation. Proposed algorithm has achieved the optimal solution with Maximum Utilization of Wavelength Converter 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.

Access-metro convergence networks (AMCN) have been proposed as a future optical communication network to realize flexible and dynamic bandwidth allocation. An AMCN requires transceivers with different wavelengths for the optical network units (ONUs). This causes an increase in production costs. Although an all-optical wavelength converter (AOWC) mitigates this issue, the AOWC increases the installation cost because it consists of many expensive optical devices. We propose the use of a remotely pumped AOWC (RP-AOWC) with an AMCN. The proposed technique can reduce the number of pump light sources in the AOWC. This paper demonstrates this reduction in the number of light sources and the feasibility of wavelength conversion using pump light propagation. We calculate the reduction in the number of pump sources and the number of transceiver types caused by the use of RP-AOWC and experiment with the wavelength conversion using pump light propagation.

Metaheuristic hybridizations for the regenerator placement and dimensioning problem in sub-wavelength switching optical networks

GMPLS grew out of MPLS, a packet-switching technology designed to improve the efficiency of data networks. In this paper, we discuss the GMPLS technology, analyze its application. GMPLS is an advanced protocol which is essential for managing a diverse and complex network, because service deployment and service provisioning are manual, lengthy and costly processes. GMPLS has caused technical challenges in its deployment in optical networks. These challenges can be generalized into two areas: label assignment and wavelength conversion capability. In regard to wavelength conversion, which is correlated to routing problems. The inability of the optical switch to perform wavelength conversion has yielded a routing problem. The incompatibility of optical devices has violated the algorithms of path determination. It results in a high blocking factor call a long the path and high latency; these would eventually prejudice the performance of optical networks.

This paper studies the overall energy consumption of a pan-European optical transport network for three different time periods: today and in five and ten years from now. In each time period the pan-European network was dimensioned using traffic predictions based on realistic data generated by the optical networking roadmap developed in the framework of the European project Building the Future Optical Network in Europe—BONE. A wavelength routed wavelength division multiplexed optical network based on either transparent or opaque node architectures was examined considering exclusively either 10 Gbit/s or 40 Gbit/s per channel data rates. The results manifest that transparent optical networking technologies are expected to provide significant energy savings of the order of 35% to 55%. It was also shown that the migration towards higher data rates, i.e., from 10 Gbit/s to 40 Gbit/s, is assisting in improving the overall energy efficiency of the network.

Hardware implementation of artificial neural networks facilitates real-time parallel processing of massive data sets. Optical neural networks offer low-volume 3D connectivity together with large bandwidth and minimal heat production in contrast to electronic implementation. Here, we present a conceptual design for in-fiber optical neural networks. Neurons and synapses are realized as individual silica cores in a multi-core fiber. Optical signals are transferred transversely between cores by means of optical coupling. Pump driven amplification in erbium-doped cores mimics synaptic interactions. We simulated three-layered feed-forward neural networks and explored their capabilities. Simulations suggest that networks can differentiate between given inputs depending on specific configurations of amplification; this implies classification and learning capabilities. Finally, we tested experimentally our basic neuronal elements using fibers, couplers, and amplifiers, and demonstrated that this configuration implements a neuron-like function. Therefore, devices similar to our proposed multi-core fiber could potentially serve as building blocks for future large-scale small-volume optical artificial neural networks.

We propose a hierarchical optical path network design algorithm that considers wavelength conversion. Numerical experiments prove that, by employing wavelength conversion, hierarchical optical path networks will be more cost effective than single-layer optical path networks over a wide range of traffic demand, which is not possible without using wavelength conversion.