Some networks support reservations of bandwidth along paths. For
example, various optical networks support light-path set up,
essentially allowing for an arbitrary topology to be configured. The
ODIN software [25] provides an application
with an API to exploit such networks. However, it is the onerous task
of the programmer to determine the appropriate topology and then use
the API to configure it. Here, the VMDs could do the same on behalf
of the unmodified application, since they collectively know 
.
Light-path services, as well as traditionally ISP-level reservations such as DiffServ [28], could also be used to implement an engineered overlay that is shared by multiple users, as described previously.