Data transfer occurs between an ISP database (21) and a vending machine database (11), via respective controllers (22 and 121). TCP ports and sockets (e.g. Telnet) (125, 126) at the module controller (121) and (225, 226) at the database controller (22) are used to establish separate CONTROL and CLEAR channels. The CONTROL channel provides end-to-end control information between the remote module controller (121) and the database controller (22), whilst the CLEAR channel is available to exchange pure end-to-end data.