In multi-granular optical networks

in order to meet the requests for variable service bandwidths

lower the blocking rate for high-bandwidth service requests and reduce network resource waste in low-bandwidth service request access

we propose a layered virtual topology-based trans-granularity layer survivability enhancing method.With this method

we first design a layered virtual topology according to wavelength and waveband granularities and then calculate the working and protection paths on each granular or trans-granular layer according to service request bandwidths.Analytical results show that this method can effectively improve network resource utilization ratio and reduce blocking probability.