Control of multicast traffic

The present invention relates to a multicast traffic control unit (21) for use in a data communication system (1) operable to transmit multicast traffic, and adapted: to receive membership reports (41 to 45) from at least one station (11 to 13), whereby memberships of multicast groups are notified, to report at least one membership (41, 44) out of said memberships to a multicast router (31) of the data communication system. A multicast traffic control unit according to the invention is further adapted, before reporting the at least one membership to the multicast router: to estimate a total amount (X) of multicast traffic which the multicast router would supposedly forward towards the at least one station on account of the at least one membership, to select the at least one membership such that the so-estimated total amount does not exceed a configurable threshold (Xmax).