...

The MCT "Rearranger" is the method used to move data between coupler and components.   The Rearranger has options to use either multiple MPI_Send/Recvs or mpi_alltoall.   For a more complete explanation of how MCT uses its GlobalSegmentMap and AttributeVectors to do parallel communication, see https://journals.sagepub.com/doi/abs/10.1177/1094342005056116

Time integration in other components

The atmosphere model:  Timestepping within the ACME v1 Atmosphere Model