Dynamic path switching in lower layers such as optical or sub-wavelength layer-1 path connections is essential for future
networks to provide end-to-end, bandwidth-guaranteed, large-capacity services without energy crunch. While this is
almost generally agreed, the number of ports in optical switches tends to be limited by technological difficulties, severely
restraining the scale of the network. However, video-related services, that occupies most of the traffic nowadays, could
significantly alleviate such restraints if we utilized the nature of video usage. In most cases, video-related services are
virtually provided through prior reservation scheme in which a relatively high call-blocking probabilities or long latency
for a connection can be tolerated. This situation allows us to accommodate a relatively high number of subscribers with a
limited number of switch ports.
This paper shows that a network using optical switches with a technologically feasible number of ports, multi-granular
paths, and a hierarchical network topology can be of a national scale accommodating several tens of millions of
subscribers. The purpose of detailing a plausible network topology is to show that such a network offers a benefit of
energy efficiency approximately three orders of magnitude compared with that extrapolated from recent router-based
We then discuss important technical aspects of such dynamic optical path networks including our several research
activities. We emphasize the importance of vertically integrated research activities from application to device layers to
develop the dynamic optical path networks.