1. A method for handling streams multicast over a communications system having a communications path between a content provider and a plurality of users via a broadcast system, the communications path comprising a shared forward link over which bandwidth resources are shared during a multicast communication, the method comprising: receiving a metadata stream at a network interface system of a user terminal, the network interface system being configured to receive stream data from the content provider over the communications path at a lower layer subsystem, the lower layer subsystem being configured to determine whether to accept or ignore the stream data according to a stream identifier and to pass at least some of the stream data to a higher layer subsystem when it is determined to accept the stream data according to the stream identifier, the metadata stream being received in association with the stream identifier configured to direct the lower layer subsystem to accept the metadata stream and to pass metadata to the higher layer subsystem, and the metadata stream comprising the metadata configured to describe a plurality of content atoms to be subsequently communicated over a broadcast stream and to associate each of the plurality of content atoms with an atom identifier; determining at the higher layer subsystem whether to accept the content atom as a function of a set of user preferences; when it is determined to accept the content atom, communicating the atom identifier associated with the content atom from the higher layer subsystem to the lower layer subsystem; receiving the content atom in association with the atom identifier over the broadcast stream subsequent to determining to accept the content atom; and determining at the lower layer subsystem to accept the content atom as a function of the atom identifier.