  Nanocommunications, understood as communications between nanoscale devices,
is commonly regarded as a technology essential for cooperation of large groups
of nanomachines and thus crucial for development of the whole area of
nanotechnology. While solutions for point-to-point nanocommunications have been
already proposed, larger networks cannot function properly without routing. In
this article we focus on the nanocommunications via Forster Resonance Energy
Transfer (FRET), which was found to be a technique with a very high signal
propagation speed, and discuss how to route signals through nanonetworks. We
introduce five new routing mechanisms, based on biological properties of
specific molecules. We experimentally validate one of these mechanisms.
Finally, we analyze open issues showing the technical challenges for signal
transmission and routing in FRET-based nanocommunications.
