Dominic A. Schupke

Optimal configuration of p-cycles in WDM networks

We investigate the deployment of p-cycles (preconfigured protection cycles) in WDM mesh networks with and without wavelength conversion. We develop optimization models for the configuration of the cycles and apply these on a case study for a pan-European network. The results in particular for wavelength converting networks show that p-cycles achieve high efficiency.

Cost modeling and evaluation of capital expenditures in optical multilayer networks

Optical multilayer networks offer a high degree of freedom in network design, adapting to actual network requirements (demand types, topologies, etc.) and achieving cost-efficient realizations. Capital expenditures are one of the key differentiators for the evaluation of multilayer networks. A realistic cost model for Internet protocol/multiprotocol label switching (IP/MPLS), carrier-grade Ethernet, synchronous digital hierarchy/optical transport network (SDH/OTN), and WDM equipment from which overall capital expenditures can consistently be derived is contributed and discussed. A comprehensive collection of detailed cost values for different equipment types is presented. Furthermore, the cost model is applied to two case studies, one IP/MPLS-over-WDM study and one WDM study with two topologies, showing substitution effects of network elements to achieve overall capital expenditure minimization.

Strategies for enhanced dual failure restorability with static or reconfigurable p-cycle networks

We suggest methods for achieving high dual-failure restorability in p-cycle networks that are optimally designed only to withstand all single failures, or have minimized amounts of additional capacity for dual failure considerations. In one set of circumstances we consider static p-cycles (that cannot be rearranged once established) and propose strategies to enhance the dual-failure restorability based on concepts of failure spreading and limiting the maximum number of protection relationships of any p-cycle. We then consider the case of reconfigurable p-cycles, in which the spare capacity can be reconfigured dynamically, creating a new set of p-cycles that are optimized to withstand possible second failures. Results show significant improvements of the dual-failure restorability obtained by limiting the number of protection relationships in static design. For 100% dual-failure restorability, p-cycle reconfiguration reusing most of the existing p-cycles and adding some new ones appears to be the most promising approach.

A matrix-based analytical approach to connection unavailability estimation in shared backup path protection

This letter introduces a matrix-based approach to connection unavailability estimation in shared backup path protection (SBPP). The proposed approach yields accurate results for networks of national size using simple matrix operations, being therefore suitable for online routing algorithms. The accuracy of the unavailability estimates is verified through simulations.

Capacity Efficiency and Restorability of Path Protection and Rerouting in WDM Networks Subject to Dual Failures

Resilient optical networks are predominately designed to protect against single failures of fiber links. But in larger networks, operators also see dual failures. As the capacity was planned for single failures, disconnections can occur by dual failures even if enough topological connectivity is provided. In our approach the design of the network minimizes the average loss caused by dual failures, while single failures are still fully survived. High dual failure restorability is the primary aim, capacity is optimized in a second step. For WDM networks with full wavelength conversion, we formulate mixed integer linear programming models for dedicated path protection, shared (backup) path protection, and path rerouting with and without stub-release. For larger problem instances in path rerouting, we propose two heuristics. Computational results indicate that the connectivity is of much more importance for high restorability values than the overall protection capacity. Shared protection has similar restorability levels as dedicated protection while the capacity is comparable to rerouting. Rerouting surpasses the protection mechanisms in restorability and comes close to 100% dual failure survivability. Compared to single failure planning, both shared path protection and rerouting need significantly more capacity in dual failure planning.

Performance of path protection and rerouting for WDM networks subject to dual failures

The restorability and the needed capacity of (dedicated and shared) path protection and rerouting in sample networks planned for dual failures are presented. The rerouting performance is related to single failure designs. Dual failures become more probable in larger networks and should be considered when planning and operating such networks.

The tradeoff between the number of deployed p-cycles and the survivability to dual fiber duct failures

p-Cycles can attain high capacity efficiency and fast protection switching times in WDM networks. The number of deployed p-cycles and the ability to survive dual fiber duct failures are further important characteristics which are considered in a pan-European network case study. We show that the dual failure restorability and the protection capacity can vary significantly for cycle-configurations with different numbers of deployed p-cycles.

On routing and transmission-range determination of multi-bit-rate signals over mixed-line-rate WDM optical networks for carrier ethernet

Ethernets success in local area networks (LANs) is fueling the efforts to extend its reach to cover metro and long-haul networks. This new Ethernet is refereed to as Carrier Ethernet. Among the various transport infrastructures for realizing Carrier Ethernet, wavelength-division multiplexing (WDM) optical network is a strong candidate for this purpose. Optical transmission rates per channel are increasing from 10 to 40 Gb/s and even 100 Gb/s, and they can also coexist in the same fiber. Along with the flexibility associated with such a network with mixed-line rates (MLR), signal-related constraints at high rates become a challenge for cost-efficient routing. Among these issues is the maximum nonregenerated optical distance that a signal can travel before its quality degrades or maximum transmission range (TR). TR is rate-dependent: The higher the rate, the shorter the range. While high-rate pipes may require signal regeneration to restore the signals quality, they support more traffic and, hence, can save resources. We study the problem of cost-efficient routing of multi-bit-rate (1/10/40/100 Gb/s) Ethernet tunnels using MLR over a carriers WDM optical network with signal-transmission-range constraints. We studied the effect of TR for mixed-rate signals (10/40/100 Gb/s) on the networks cost to determine the optimal TR of each bit rate. We present an analytical model based on a mixed-integer linear program (MILP) to determine the optimal TR of a small network. Since MILP has scalability constraints that makes it hard or sometimes impossible to solve for real network topologies, we propose a graph-based solution that constructs a mixed-line-rate auxiliary (MLR-AUX) graph to capture the networks heterogeneity and a weight-assignment approach that allows the routing to be cost-efficient. Our algorithms were tested on a U.S. nationwide network topology. We found that it is possible to reduce the networks cost by using short TR and that the optimal TR depends strongly on traffic characteristics and on the TR values of different bit-rate signals.

Analysis of p-cycle Capacity in WDM Networks

Abstract.The concept of p-cycles provides many characteristics, which are benficial for deployment and operation in WDM networks. We present a detailed analysis of the resource efficiency addressing several issues, which are essential to WDM networks. This includes novel investigations about the influence of the length of working paths and a detailed redundancy comparison of p-cycles with prevalent protection mechanisms. In addition, we find several trends in the optimal p-cycle network design. One is the capacity smoothing effect that can be related to analytical capacity bounds. We can also identify that shorter p-cycles can facilitate optimal design in demand hot-spot regions. Finally, we propose a novel concept of p-paths, which, when used additionally in a p-cycle design, is able to improve capacity efficieny. This concept is also interesting in terms of both theoretical bounding conditions and practical deployment.

Cost Comparison of Networks Using Traditional 10 and 40 Gb/s Transponders Versus OFDM Transponders

OFDM allows flexible adjustment of transmission data rate according to channel properties. We propose to use OFDM transponders and calculate the cost at which OFDM networks result in lower CAPEX compared to traditional networks.