  We develop a theory and accompanying mathematical model for quantum
communication via any number of intermediate entanglement swapping operations
and solve numerically for up to three intermediate entanglement swapping
operations. Our model yields two-photon interference visibilities post-selected
on photon counts at the intermediate entanglement-swapping stations. Realistic
experimental conditions are accommodated through parametric down-conversion
rate, photon-counter efficiencies and dark-count rates, and instrument and
transmission losses. We calculate achievable quantum communication distances
such that two-photon interference visibility exceeds the Bell-inequality
threshold.
