Abstract: A method of controlling communication between a head-end system and a number of client systems through a network, wherein, for each receiver, only a nearest one of the multicast router systems in the network is configured to forward a copy of a message addressed to the multicast groups of which the receiver is a member directly to the receiver, includes: maintaining subscriber group information linking each registered one of the number of client systems to an associated one of a plurality of subscriber groups, and allocating registered client systems to at least one multicast group, such that all client systems associated with a particular subscriber group are in a common multicast group. Information uniquely identifying the nearest multicast router system nearest to a receiver for a first client system is obtained, and the first client system is assigned to a subscriber group including at least one further client system having the same nearest multicast router system.

Abstract: Methods and systems are disclosed in which contact can be safely distributed and protected in a manner that is viable in terms of bandwidth economy and ensures that clients can be identified by the content received. Copies of encrypted content can be provided such that unique watermarks can be added to the copies. Content can also be both watermarked uniquely for multiple clients and multicasted to the clients. As such, content can be distributed using the bandwidth efficiency of multicasting while providing reliable content protection and watermarking.