Multipath optical routing with compact fiber delay line-based differential delay compensation

Multipath (MP) routing is an effective technique for applications imposing stringent requirements on bandwidth, delay and availability. However, the benefits of MP routing can be impaired by the differential delay (DD) i.e., delay difference between paths of the MP connection. In presence of DD the destination of a MP connection receives a disordered version of the original packet sequence. Thus, a DD compensation (DDC) technique is needed to recover the original sequence. DDC is normally performed at destination (centralized-DDC) using high speed reconstruction buffers. For MP connections with large DD the centralized-DDC creates a bottleneck that limits the performance gain of MP routing. DDC can be distributed along the paths (distributed electronic-DDC) to reduce the reconstruction buffer requirements and minimize DD at destination. In optical networks, distributed electronic-DDC incurs in extra costly and power hungry electro/optical (E/O) conversions, that are otherwise avoided by routing all optical circuits (i.e., lightpaths). To avoid extra E/O conversions, distributed electronic-DDC can be jointly placed with optical regeneration. Nonetheless, such approach greatly reduces the candidate nodes to distribute the DDC, because optical regeneration is only needed for very long lightpaths. This work proposes, for the first time, the use of compact fiber delay lines (FDL)s to perform distributed all optical DDC (transparent-DDC). The FDLs are passive elements that overcome the problems of previous solutions: they are not restricted to optical regeneration points, and do not incur into extra E/O conversions. An integer linear programming formulation is presented for the MP routing with DD-minimization problem that combines electronic-DDC co-located with 3R (Reamplifying, Reshaping and Retiming) regeneration points to the novel transparent-DDC based on FDLs. Numerical results show the advantages of combining transparent and electronic-DDC in realistic network scenarios.