A service platform for a content delivery network indicates a transmission rate cap to be imposed when streaming data to a data requesting device over an access network. Means are provided for receiving a service request for delivery of data from a requesting device as the result of which the requested data is delivered as a prioritised traffic stream over an access link to the requesting device. The service platform processes the service request to determine one or more performance characteristics of said access link and uses this to determine the maximum transmission rate for the requested data to be streamed at over the access link during its delivery to the requesting device. This information is included in a source address for the requested data which the service platform generates, typically as a URL. The maximum transmission rate set is provided as a prefix to the URL (or in some other meta-data format) to the requesting device, and the content delivery platform is configured to ensure that requests for media assets which are received at the logical or virtual ports associated with the URL pre-fixes are responded to by transmissions limited to the maximum bandwidth cap indicated by the URL pre-fix.