An access point (AP) transmits a first frame comprising a medium synchronization duration for a first channel. The AP receives, via a second channel, a second frame comprising a duration field indicating a first duration for transmission or reception of one or more frames on the second channel after the second frame. After receiving the second frame and during a medium synchronization duration for the first channel, the AP transmits, via the first channel, a third frame indicating a second duration overlapping with the first duration.