The invention relates, in particular, to a system for managing communication sessions between first terminals adapted to send audio and/or video and/or data streams during these sessions and second terminals accessible via an external data transmission network. The first terminals are connected to a stream concentrator itself connected to the external network. Since the streams sent by at least some of the first terminals are coded or intended to be coded by hierarchical encoders, the system includes means for processing said streams so that each of them is sent to the external network by the concentrator at a given hierarchy level and means for determining said hierarchy level as a function of parameters relating to the number and nature of the sessions set up between the first terminals and the second terminals.