The present invention, generally speaking, provides for sharing of bandwidth of a shared medium between multiple devices. In one embodiment, the shared medium is structured in accordance with a frame or superframe structure, each frame or superframe having medium access slots of specified time duration defined therein, groups of N contiguous medium access slots defining different allocations zones, groups of M medium access slots defining coordinated sets of medium access slots, wherein the medium access slots of a coordinated set belonging to different allocation zones are equally spaced in time. A device identifies a reservation as regular or irregular, wherein a regular reservation causes the entire medium access slots in one or more coordinated sets to be allocated. In the case of either a regular or an irregular reservation, allocating medium access slots such that a number of unallocated contiguous medium access slots within each allocation zone is maximized. The contiguous unallocated medium access slots separate the group of regular allocations and the group of irregular allocations within each allocation zone.