Elastic optical networks (EONs) enable network operators to have agile bandwidth management in the optical layer. In this paper, we investigate dynamic and adaptive bandwidth defragmentation (DF) in EONs with time-varying traffic using connection reconfigurations. We consider how to design DF procedure in a systematic way, and study the problems that have not been fully explored so far. Basically, we divide the procedure design into four subproblems: “How to reconfigure?,” “ How to migrate traffic?,” “When to reconfigure?,” and “What to reconfigure?,” and solve them sequentially. For “How to reconfigure?,” we investigate the combination of routing and spectrum assignment (RSA) algorithms for DF, i.e., the RSA algorithm that the connections are originally served with and the algorithm that they are re-optimized with. For “ How to migrate traffic?,” we propose to construct a dependency graph to represent the relations among the selected connections and to use it to assist the best-effort traffic migration. A move-to-vacancy method is also proposed to further reduce the traffic disruptions. For “When to reconfigure?” and “ What to reconfigure?,” we propose intelligent timing selection and adaptive DF ratio selection methods to tackle the tradeoff between the bandwidth blocking probability (BBP) performance and operational complexity. Simulation results show that the algorithm with both methods implemented (DF-AT-AR) achieves better tradeoff between BBP performance and operational complexity, when compared with existing algorithms.

Dynamic and Adaptive Bandwidth Defragmentation in Spectrum-Sliced Elastic Optical Networks With Time-Varying Traffic

Bandwidth defragmentation, i.e., the operation to reconfigure existing connections for making the spectrum usage less fragmented and less misaligned, has recently been recognized as one of the most important features for elastic optical networks (EONs). In this paper, we propose a novel comprehensive bandwidth defragmentation algorithm that considers the problems of 1) When to defragment? 2) What for defragment? and 3) How to defragment? jointly. The proposed algorithm accomplishes defragmentation through proactive network reconfiguration that only reroutes a portion of existing connections. In each defragmentation operation, we first choose the connections to reroute using a selection strategy, then determine how to reroute them with the defragmentation based routing and spectrum assignment (DF-RSA), and finally perform rerouting with best-effort traffic migration to minimize traffic disruptions. Simulation results indicate that in order to make the bandwidth blocking probability (BBP) comparable with that from the Greenfield scenario (100% rerouting all the time), the proposed algorithm only needs to reroute ~30% existing connections. The simulations also demonstrate that the traffic disruption percentages are less than 1% for defragmentations with 30% rerouting and can be further reduced to within 0.25% by adding a move-to-vacancy (MTV) approach in the traffic migration.

Bandwidth defragmentation in dynamic elastic optical networks with minimum traffic disruptions

Elastic optical networks (EONs) facilitate agile spectrum management in the optical layer. When coupling with software-defined networking, they function as software-defined EONs (SD-EONs) and provide service providers more freedom to customize their infrastructure dynamically. In this paper, we investigate how to overcome spectrum fragmentation in SD-EONs with OpenFlow-controlled online spectrum defragmentation (DF), and conduct system implementations to facilitate highly-efficient online DF. We first consider sequential DF, i.e., the scenario that involves a sequence of lightpath reconfigurations to progressively consolidate the spectrum utilization. We modify our previous DF algorithm to make sure that the reconfigurations can be performed in batches and the “make-before-break” scheme can be applied to all of them. The modified algorithm is implemented in an OpenFlow (OF) controller, and we design OF extensions to facilitate synchronous batch reconfiguration. Then, we further simplify the DF operations by designing and implementing parallel DF that can accomplish all the DF-related lightpath reconfigurations simultaneously. All these DF implementations are experimentally demonstrated in an SD-EON control plane testbed that consists of $14$
 stand-alone OF agents and one OF controller, which are all implemented based on high-performance Linux servers. The experimental results indicate that our OF-controlled online DF implementations perform well and can improve network performance in an efficient way.

Demonstrations of Efficient Online Spectrum Defragmentation in Software-Defined Elastic Optical Networks

Lightpath reconfiguration is a networking task that can be performed in order to improve resource utilization. The lightpath reconfiguration problem becomes nontrivial when a new set of lightpaths requires the release of resources previously seized by the (working) lightpaths currently in place, but, in order to ensure continuity of the traffic flow, the working lightpaths cannot be torn down before the new ones are set up. Under this condition the reconfiguration can fall into a deadlock state, and deadlocks can only be solved by temporary disruption of some connections. At this point, traffic disruptions are necessary, and network operators must compensate customers with penalty fees for the service disruption. In this paper we focus on minimizing the number of simultaneously disrupted connections at any time during the reconfiguration process. In this paper, we propose a mixed-integer program (MIP) model, an exact algorithm, and a heuristic for solving the problem considering our objective.

Lightpath Reconfiguration in WDM Networks

A survey of WDM network reconfiguration: Strategies and triggering methods

Optical networks employing wavelength division multiplexing can carry huge volumes of traffic, hence maintaining a high level of service availability is important. This makes fault tolerance an important issue. In general the failed connections need to be rerouted. After a link or node failure, alternate paths for restoration of the failed connections may exist only if the network is reconfigured. In addition to link or node failure scenarios, connection rerouting or network reconfiguration may also prove helpful for accommodating new requests which may otherwise be blocked. Since connections on backbone optical networks, have longer call durations, it is crucial to accommodate new blocked requests through alternate means, instead of blocking them till existing connections terminate and make a path available. These situations make network reconfiguration important. Since most connections plying on todays backbone networks are high data rate connections, it is critical that the connections have minimal disruption times during network reconfiguration. In this paper, we propose a methodology for minimizing the disruption time and the number of disruptions in the network during connection rerouting.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=20443&context=rtd

N. Jose

Papers

Connection rerouting/network reconfiguration