A spinal fusion system for positioning between two vertebral bodies is presented. The ring has a plurality of channels adapted to receive retaining features of the implantable medical device to stabilize the medical device within the jar. The system stores associatively with the user address a limit on the user’s use of the requested product; in a specific embodiment a time period during which the movie can be viewed, or the number of times the movie can be viewed, or both, even though the data transmission channel between the user and head end is not in use continuously. The test components process the commands concurrently, generating results.