Time-Spectrum Consecutiveness Based Scheduling With Advance Reservation in Elastic Optical Networks

Novel advance reservation (AR) requests, such as user data replication and grid computing, which are different from immediate reservation requests, allow certain initial-delay during setting up, as long as the resources are allocated before a preset deadline. Empowered by the optical orthogonal frequency-division multiplexing (O-OFDM) technology, the elastic optical networks (EON) support channels operating at heterogeneous line rates by allocating spectral resources in a flexible and dynamic manner. However, in a dynamic traffic scenario, dynamic path setup and teardown operation will inevitably lead to spectral fragmentation. In this paper, to effectively allocate the spectrum in a suitable duration along a better route, we introduce a notion of available time-spectrum consecutiveness (TSC) to describe the spectrum fragmentations along frequency axis and time axis. Based on TSC, three time-aware routing and spectrum assignment (RSA) algorithms are proposed. The novel algorithms retain the TSC as much as possible when establishing a lightpath and reduce the spectrum fragmentation. Simulation results indicate three proposed algorithms achieve lower blocking probability and higher spectrum efficiency.