The present disclosure includes systems and techniques relating to controlling access to a shared communication medium in a wireless communication system. In some implementations, a first communication device associated with a first basic service set (BSS) identified by a first BSS indicator receives a data unit transmitted by a second communication device. The data unit includes (i) a second BSS indicator indicating a second BSS associated with the second communication device and (ii) a duration indicator indicating a duration of time for which the shared communication medium is expected to be busy. An inter-BSS channel access counter is set based on the duration of time indicated by the duration indicator if the second BSS is different from the first BSS. An intra-BSS channel access counter is set based on the duration of time indicated by the duration indicator if the second BSS is the same as the first BSS.