  This paper investigates the performance of a two-tier AWGR-based Passive
Optical Network (PON) data centre architecture against an AWGR-based PON data
centre architecture by considering various scenarios involving link failures to
evaluate the resilience of both designs. To optimize traffic routing under
different failure scenarios, a Mixed Integer Linear Programming (MILP) model is
developed and the power consumption and delay performance is assessed. The
results demonstrate that the two-tier AWGR architecture reduced the power
consumption and the delay compared to the AWGR-based architecture by up to 10%
and 61%, respectively.
