A method of selecting a suitable service for the delivery of a communication across an integrated network is disclosed. Before now, users had to select the service that best suited their needs at the time of each delivery. By providing a computer programmed to act as a purchasing agent with data indicating the desirability of stability in the network service (that data representing the price the user is prepared to pay for stability) an automatic selection of the service to be provided to the communication is enabled. An embodiment is described in which different degrees of stability are given to different content file deliveries in dependence on the importance attached to the recipient by a content provider. The invention could equally be used to provide an appropriate services for many different types of network traffic.