Algorithmic Aspects in Planning Fixed and Flexible Optical Networks With Emphasis on Linear Optimization and Heuristic Techniques

Spectrum engineering in flexible grid data center optical networks

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.

Service differentiation-based spectrum defragmentation in mixed grid optical networks

In this paper, we have proposed a generalized large-scale optical cross-connect (OXC) architecture utilizing waveband selective switches (WBSS) for realizing future cost-effective, bandwidth-abundant and flexible optical networks. The developed architecture implements multiple WBSSs for each incoming fiber and small size wavelength selective switches (WSSs) for dropping optical paths while simply deploying 1´2 WSSs or 1´2 optical couplers for realizing the adding function. Thanks to the use of WBSSs, which are more cost-effective and simpler devices, the developed architecture enables a significant hardware scale reduction. The WBSS-based OXC, however, suffers from a limited routing capability, which relies on the inner node parameter (i.e., the WBSS number per input fiber) and the waveband granularity of WBSSs. We, therefore, evaluate the hardware scale requirement of our developed architecture in comparison with that of conventional WSS-based OXC. It is verified that a substantial hardware scale reduction can be achieved by using the proposed architecture, especially for high port count OXCs or when applying coarser granular WBSSs. Moreover, we also assess the performance of dynamic optical networks based on the proposed OXC. Numerical simulations show that the network offers a substantial necessary hardware scale reduction at the cost of a small performance offset comparing to that of the network using conventional WSS-based OXC.

Flexible energy-efficient and direct intra-ODN/OPN communication capable TWDM PON architecture with centralized OLT sharing among multiple optical networks

The routing and spectrum assignment (RSA) is one of the key problems in flexible optical networks. When in a gridless fashion, the shortest-path RSA algorithms have exponential computational complexity, and are thus not suitable to be employed in real networks. On the other hand, today most optical components cannot support fully gridless tunability, which also limits the application of gridless RSA schemes. In this paper, we propose a novel grid-based spectrum-scan routing (SSR) scheme in flexible optical networks. The SSR scheme achieves optimal routing with a polynomial computational complexity. Compared with other RSA schemes, SSR has shorter computation time, lower blocking probability, and higher resource utilization.

With the rapid growth of traffic and power consumption in information and communication technology industry for decades, improving energy efficiency has become a challenging issue in recent years. Especially, the pervasive access to Internet via mobile devices will cause wireless traffic volume increment by 1000+ times in near future, which is expected to be carried by the fifth generation ultradense cellular network. Following this trend, the core network where optical fibers are deployed to deliver aggregated traffic needs upgrading to accommodate the increasing traffic volume. To match with the traffic growth rate, we should conduct efficient network planning over multiple time periods. Moreover, considering the heterogeneity in the bandwidth requirements among various network services, flexible mixed line rate scheme is adopted in network provisioning. In this paper, we study the long‐term multiperiod planning of optical core network by considering the traffic growth with the objective of high energy‐efficiency. Three planning strategies, say All‐period, Incremental, and End‐of‐Life, respectively, are studied and formulated as mixed integer linear programming models with the objective to minimize power consumption of optical core network. Given the estimation on the reduction of power consumed by various network devices, we can deploy network devices flexibly in each period through the optimization models. Performance of the proposed models is also evaluated and compared via case studies.

Survey of resource allocation schemes and algorithms in spectrally-spatially flexible optical networking

Compared to traditional wavelength division multiplexing (WDM) networks, orthogonal frequency division multiplexing (OFDM)-based flexible optical networks provide better spectral efficiency due to their flexible bandwidth allocation capability and fine granularity. Survivability is a crucial issue in OFDM-based flexible optical networks. Recently we proposed a new survivable multi-path provisioning scheme (MPP) that efficiently supports demands with flexible protection requirement in OFDM-based optical networks and studied the static survivable multipath routing and spectrum allocation (SM-RSA) problem, which aims to accommodate a given set of demands with minimum utilized spectrum. We have showed that the MPP scheme achieves higher spectral efficiency than the traditional single-path provisioning (SPP) scheme. In this paper, we study the dynamic SM-RSA problem, which selects multiple routes and allocates spectrum on these routes for a given demand as it arrives at the network. We develop an integer linear programming (ILP) model as well as a heuristic algorithm for the dynamic SM-RSA problem. We conduct simulations to study the advantage of MPP over SPP for the dynamic traffic scenario in terms of blocking performance and fairness. We also compare the performance of the MPP heuristic algorithm and the ILP model.

Flexible optical networks, based on bandwidth-variable optical cross-connects (BV-OXCs) and novel flexible transponders, are expected to significantly improve the overall spectrum efficiency with respect to traditional networks where fixed frequency spacing is applied. Flexible optical networks will exploit the BV-OXC capability to dynamically configure the reserved bandwidth as a set of frequency slots. In addition, flexible transponders will be employed to dynamically configure transmission parameters, such as bit-rate and modulation format. To enable these new configuration capabilities, network operation enhancements need to be efficiently introduced and investigated. In this study, we focus for the first time on the Path Computation Element (PCE) architecture for flexible optical networks. PCE architecture and PCE communication protocol are enhanced to maximize the spectral efficiency and to provide indications also on the specific transmission parameters to configure. Experimental demonstration is provided through two different experiments, successfully showing the PCE capability to trigger dynamic rerouting with bit-rate or modulation format adaptation. In particular, the experiments demonstrate, in a real testbed, dynamic frequency slot assignment and format adaptation from DP-16QAM to DP-QPSK at 100 Gb/s, and bit-rate adaptation at DP-16QAM from 200 Gb/s to 100 Gb/s.

Flexible optical networks appear as the most prevalent candidates for next-generation core transport networks. The transition from a fixed to a flexible frequency grid calls for novel spectrum allocation techniques. This work focuses on the notion of dynamic cooperative spectrum sharing and addresses the issue of dynamic cooperative spectrum allocation for flexible optical networks. In orderto cope with the dynamicity of the traffic demands, spectrum expansion/contraction (SEC) policies attempt to accommodate incoming requests by means of expanding/contracting the allocations of connections. When spectrum expansion is limited by neighboring connections, appropriate spectrum defragmentation (SD) policies undertake the task of reallocating connections in order to free up the spectrum. In this work, a novel cooperative SEC policy is examined, which takes into consideration the spectrum allocation of neighboring connections. Additionally, a class of cooperative SD policies is proposed, based on the capabilities of current technology. Simulation results from two reference core networks quantify the benefits that can be reaped in terms of blocking rate. Trade-offs with respect to the achieved reduction in blocking rate and the number of reallocated connections during the SD procedure are examined.

We present a network planning and operation tool, called Mantis, for designing the next generation optical networks, supporting both flex-grid and mixed line rate networks. Through Mantis, the user is able to define the network topology the traffic matrix, the CAPEX/OPEX parameters, setup basic configuration parameters, and use a library of algorithms to plan, operate, or evaluate an optical network of interest. Mantis is designed to be deployed either as a desktop application or as a cloud service. For its execution Mantis can utilize the services of the Amazon Elastic Compute Cloud (Amazon EC2) , however its modular architecture allows other cloud services to be adopted in the future with minimum effort. Using the cloud services Mantis can scale based on the user demands, executing fast and efficiently the scenarios requested. The included planning and operation algorithms range from routing, to equipment placement and to wavelength and spectrum allocation and others.

The sliceable bandwidth-variable transponder (SBVT) has been recently proposed as a transmission module able to combine the scalability of superchannel-based transmission with the flexibility required for highly meshed traffic. The modular nature of the SBVT implies that a large array of transmission capacity is predeployed per module, which significantly affects the planning and dimensioning of backbone optical networks. These planning methods should also account for the switching modules that are required to support the interconnection between the SBVTs on the line-side and the client signal interfaces. In this paper we study the impact of the switch capacity on the cost and flexibility of SBVT-enabled networks. Specifically, we propose a multiperiod planning simulation based on integer linear programming models to optimize incremental traffic deployments with respect to the cost of SBVTs, switches, and client cards. The results highlight the fact that switch capacity must be carefully balanced in order to avoid overprovisioning the switch capacity beyond the traffic requirements, while at the same time providing enough flexibility in the client-to-line interconnection to do efficient lightpath grooming and therefore reduce client-card- and SBVT-related costs.

Space-division multiplexing allows unprecedented scaling of bandwidth density for optical communication. Routing spatial channels among transmission ports is critical for future scalable optical network, however, there is still no characteristic parameter to label the overlapped optical carriers. Here we propose a free-space optical flow routing (OFR) scheme by using optical orbital angular moment (OAM) states to label optical flows and simultaneously steer each flow according to their OAM states. With an OAM multiplexer and a reconfigurable OAM demultiplexer, massive individual optical flows can be routed to the demanded optical ports. In the routing process, the OAM beams act as data carriers at the same time their topological charges act as each carrier's labels. Using this scheme, we experimentally demonstrate switching, multicasting and filtering network functions by simultaneously steer 10 input optical flows on demand to 10 output ports. The demonstration of data-carrying OFR with nonreturn-to-zero signals shows that this process enables synchronous processing of massive spatial channels and flexible optical network.

With the emergence of cloud services based on data centers, demands for bandwidth-intensive applications have increased dramatically, and application services have transferred to a more diversified direction. Management as well as capacity of the backbone network needs further development to catch up with rapidly evolved application demands. Optical network virtualization can facilitate the sharing of physical infrastructure among multiple network applications. Virtual Network Embedding (VNE), the main implementation of network virtualization, determines how to map a virtual network request onto physical substrate. To expand the network capacity, flexible-grid elastic optical networks have been considered as a promising supporting technology for the future infrastructure of the next-generation Internet. However, due to the expense of key enabling equipment for flexible grid optical networks, the brown-field migration from a fixed grid to a flexible grid gave birth to the co-existing fixed/flexible grid. Based on the co-existing fixed/flexible grid optical networks, we investigate the problem of Virtual Optical Network (VON) provisioning, and present a flexible-grid-aware virtual network embedding algorithm to map the virtual networks onto the substrate network. In addition, the performance of the algorithm was evaluated under four different network scenarios. Simulation results show that the proposed algorithm can achieve better performance in all four scenarios.