Communication system and method

A method of determining information on network resources in a packet-based internetwork comprising multiple routing nodes, the method comprising:

• distributing user software to each of multiple end-user terminals connected to the internetwork by distributing a respective instance of a user application to each of the end-user terminals, the user application comprising the user software and secondary code, with the user software and secondary code being part of the same application at least in that execution of the secondary code is dependent on execution of the user software, the secondary code being distributed as part of a same download and installation process as the user software, the user software having a primary user function other than collection of network data;
• in association with the user software, distributing secondary code configured to participate in said collection of data by probing different routes from the respective end-user terminal to a destination terminal over the internetwork, each route passing via a plurality of said routing nodes;
• receiving data resulting from the probing performed by the secondary code on the multiple end-user terminals, including data resulting from routes involving the routing nodes of different network service providers, the secondary code configured to report the data resulting from said probing to a data processing facility which determines estimates of network resources based on the received data, the data processing facility configured to redirect the communication via a relaying end-user terminal in dependence on the determining estimates of network resources.