A method includes determining that a first station has been allocated a first time period to transmit over a shared medium in a network. The method includes transmitting, from the first station to a second station over the shared medium during the first time period, wherein stations other than the first station and the second station refrain from transmitting over the shared medium during the first time period. The method includes receiving, from the second station, a request message to allow the second station to transmit during the first time period and a requested amount of time to transmit. The method includes, in response to allowing the second station to transmit during the first time period, determining an authorized amount of time for the second station to transmit during the first time period, and transmitting an authorization message for the second station to transmit and the authorized amount of time.