  Data centers based on Passive Optical Networks (PONs) can provide high
capacity, low cost, scalability, elasticity and high energy-efficiency. This
paper introduces the use of WDM-TDM multiple access in a PON-based data center
that offers multipath routing via two-tier cascaded Arrayed Waveguide Grating
Routers (AWGRs) to improve the utilization of resources. A Mixed Integer Linear
Programming (MILP) model is developed to optimize resource allocation while
considering multipath routing. The results show that all-to-all connectivity is
achieved in the architecture through the use of two different wavelength within
different time slots for the communication between racks in the same or
different cells, as well as with the OLT switches.
