so far either completely or in part this allows the server to begin delivery from the most optimum point the flute protocol does not provide an interactive channel for the client device to contact the server but the existence of such a channel is an implicit part in present network scenarios it will be appreciated that sessions are uniquely identified in the flute protocol by their source addresses the arrangement described above enables a client device to switch from one e g ptp session to another e g ptm session by switching source address however the server and client device now both recognise that the new session is effectively a continuation of the old one despite the different source address fig6 is a schematic diagram illustrating the architecture of a client device 302 the client device 302 includes a receiver 601 for receiving packets from a server 301 a processor 602 is operatively connected to the receiver 601 and a carrier medium 603 in the form of a memory when an ssi is received from the server 302 the processor identifies the new source address contained therein and instructs a transmitter 604 to contact the new source address so as to continue the download in this embodiment a client program 605 is stored in the memory for causing.