A route mapping process for identifying the suitability of data sources for satisfying data requests generated by user terminals, wherein the process: searches one or more user address databases for user addresses (22, 23), searches one or more data distribution network databases (51, 52) for addresses of data sources (24A-24D), for each user address selects one or more data source address suitable for delivering data to that user address, generates a register of the selected data source addresses, the register having tag data associating user addresses with data sources the register being accessible by a content distribution server (53, 54) to identify data source addresses suitable for accession of data by the content distribution server for delivery to a user address in response to a data request received from the user address, characterized in that the register comprises a plurality of lists associated with different services, and the selection and precedence of a data source address for each list are made on the basis of network proximity for the respective service, and wherein: the data request is transmitted from the user address to a proxy server; the proxy server generates an origin message identifying the user address; the proxy server transmits the data request and the origin message to a content distribution server; the content distribution server identifies the user address from the origin message, and uses the user address to retrieve, from the register, a suitable data source address to be communicated to the user; the content distribution server returns a message to the proxy server, identifying the suitable data source address; the proxy server forwards the message identifying the suitable data source address to the user. searches one or more user address databases for user addresses (22, 23), searches one or more data distribution network databases (51, 52) for addresses of data sources (24A-24D), for each user address selects one or more data source address suitable for delivering data to that user address, generates a register of the selected data source addresses, the register having tag data associating user addresses with data sources the register being accessible by a content distribution server (53, 54) to identify data source addresses suitable for accession of data by the content distribution server for delivery to a user address in response to a data request received from the user address, characterized in that the register comprises a plurality of lists associated with different services, and the selection and precedence of a data source address for each list are made on the basis of network proximity for the respective service, and wherein: the data request is transmitted from the user address to a proxy server; the proxy server generates an origin message identifying the user address; the proxy server transmits the data request and the origin message to a content distribution server; the content distribution server identifies the user address from the origin message, and uses the user address to retrieve, from the register, a suitable data source address to be communicated to the user; the content distribution server returns a message to the proxy server, identifying the suitable data source address; the proxy server forwards the message identifying the suitable data source address to the user. the data request is transmitted from the user address to a proxy server; the proxy server generates an origin message identifying the user address; the proxy server transmits the data request and the origin message to a content distribution server; the content distribution server identifies the user address from the origin message, and uses the user address to retrieve, from the register, a suitable data source address to be communicated to the user; the content distribution server returns a message to the proxy server, identifying the suitable data source address; the proxy server forwards the message identifying the suitable data source address to the user.