Real-Time Interaction Over the Internet

This dissertation studied real-time interaction over the Internet (RTI2) in the context of remote experimentation where there is typically a person at the client side interacting with physical equipments at the server side. Remote experimentations of mechatronic equipment have strong real-time constraints due to the dynamical evolution of the behaviors to be observed and controlled. The objective of this dissertation is to propose solutions that provide the best possible feedback to the user such that the drawbacks inherent to the distance between the client and the remote equipment are minimized while providing sufficient information about the equipment state and its operational conditions. In the ideal solution, the information representing the state of the remote equipment are rendered at the same pace it has been acquired, with a minimal time delay between the acquisition phase and the rendering phase. Solutions are proposed to approach as closely as possible to this ideal solution despite the inherent variability of the Internet and the versatility of the devices used by the clients. To characterize the feedback provided to the user, a definition for the RTI2 Quality of Service is proposed which includes three properties: the level of interaction, the accuracy of dynamic rendering and the wealth of semantic content. As these three properties cannot be directly measured, three related metrics are defined. The metrics definition relies on two abstractions; the first one defines a block as a unit of information that fully describes the state and the conditions of operation of the remote equipment at a given time. The second abstraction defines an end-to-end structure that includes the communication link and both the server and the client devices. The estimated metrics are the block end-to-end round trip time, the block duration ratio and the block size ratio. To guarantee a given quality of service, a cascade end-to-end adaptation structure is proposed. This control scheme is designed to track the block round trip time by adapting the block size. The adaptation scheme and the underlying model are validated with real-world measurements. A mechanism called TCP Most-Recent is proposed as an enhancement to the TCP protocol. It alleviates the problem related to the TCP buffering mechanism, thus improving the data transmission delay. This mechanism is especially useful for applications that send perishable data as in RTI2. Perishable data are data with limited time validity, thus resending this outdated data is useless and inefficient. The tradeoff in using TCP-MR is to accept possible losses in order to gain interactivity. Such a tradeoff can be limited if the adaptation, carried out at the application level, chooses the data to be discarded according to some criteria specified at the user level. This dissertation proposes a broad but consistent foundation for studying RTI2 in the context of remote experimentation. It is build around three main contributions. First, based on the identified objectives of a successful interaction, the quality of service for RTI2 in the context of remote experimentation is defined. The associated metrics and abstractions permitting to work at the right level are also defined. Second, using the provided metrics and abstractions, an adaptation scheme to enforce the QoS provided to the user is proposed and successfully validated. Third, a mechanism called TCP Most-Recent has been proposed to improve the information transmission delay without breaking the Internet best practice.