Method and apparatus for coordinating a usage of a wireless transmission medium among a plurality of transmission units (12). The transmission medium is of a type that is utilized in accordance with a protocol having a transmission period that is comprised of a plurality of consecutively occurring transmission sub-periods. A method includes the following steps. A data structure (28a) is periodically circulated among the transmission units, the data structure being expressive of an identification of each of the transmission units and also expressive of an identification of an assigned transmission sub-period or sub-periods, if any, during which each of the transmission units is permitted to transmit on the wireless medium. The step of circulating includes the following steps: (a) receiving the data structure from a first transmission unit with a second transmission unit; (b) respsonsive to the receipt of the data structure at the second transmission unit processing the data structure in accordance with an amount, if any, of impending transmission activity to modify the assignments of sub-periods therein; and (c) transmitting the modified data structure to another one of the transmission units. A method of synchronizing the plurality of transmission units to a slotted transmission protocol is also disclosed.