This document discloses a solution for determining a channel assessment threshold in an apparatus. A method according to this solution includes: determining, by the apparatus, a channel assessment threshold based on a factor representative of a signal-to-interference ratio at another apparatus with which said apparatus has established a link; determining, by the apparatus on the basis of the channel assessment threshold, whether or not a channel is free for transmission over the link; and upon determining the channel to be free, causing transmission of a frame.