Patent ID: 7069340

Claim:
A method of operating a transmitter to transmit a data block to a plurality of recipients selected from a plurality of receivers connected to said transmitter via a multicast-capable network, wherein said transmitter has access to one or more directories storing a plurality of lists of receiver identifiers and a multicast-address suitable for use in said multicast-capable network corresponding to each of said lists; said method comprising the steps of: a) obtaining a list of receiver identifiers, said list corresponding to the set of recipients to which said data block is to be sent; b) after receiving said data block, said data block being without a corresponding multicast address, examining said one or more directories to find and obtain a multicast-address corresponding in common to said list of receiver identifiers obtained in step a); c) addressing said data block to said multicast address found and obtained in step b); and d) transmitting said data block over said multicast-capable network, the data block being addressed with said multicast address in step c).