The invention relates to a method of initializing a communications session between a plurality of terminals. According to the invention, the initialization method is adapted, as a function of capacity data for at least one terminal, to determine a set of at least one stream transmission channel to be set up between entities of a group of entities comprising said terminals, each channel being for setting up between a first entity and a second entity of the group either directly, or indirectly via at least one third entity of said group, and to transmit at least one entity identifier to at least one first entity of the group in order to set up at least one channel of the set. The invention also relates to a method of accessing a communications session, the method being adapted to receive at least one identifier of at least one entity with which at least one channel is to be set up and to set up at least one channel with at least one entity for which said at least one identifier has been received. The invention also relates to a server (S) and to a terminal (TA) respectively for performing the initialization method and the method of accessing a communications session.