Discrete-Time Sliding-Mode Controllers for MPTCP Networks

TCP provides the principal framework for the Internet traffic control. Following the protocol development, however, the communicating parties have not benefitted from the potential of multiple interfaces, now commonly installed at the end-point devices. In order to grasp new opportunities, a multipath version of TCP - multipath TCP (MPTCP) - has recently been introduced. It permits the simultaneous use of a few, diverse interfaces for enhancing the user experience. This article provides a discrete-time model of the data exchange process in the MPTCP framework and new flow control algorithms. The algorithms, applicable to the paths with nonhomogenous properties with respect to delays, loss rate, etc., are designed following the rules of discrete sliding-mode control (DSMC). As a result, direct implementation in discrete networking context and robust transmission system performance are guaranteed in uncertain operating conditions. It is formally demonstrated that a finite data queue length in the end-point buffers and a feasible (non-negative and bounded) input signal are ensured despite input and output perturbations affecting the control process. It is also shown that the classical DSMC design approach results in decreased performance for unanticipated surge in the intensity of network-related perturbations. A second, improved algorithm, with a well-chosen sliding variable, eliminates this drawback.