Non-intrusive scheduling of TCP flows

We investigate how to build a non-intrusive scheduled TCP. For the flows of a given origin-destination pair, the objective is to schedule their TCP segments (according to some desired criteria) without modifying the network bandwidth-share used by these flows, which in turn ensures friendliness with respect to the rest of the network. We show that in order for a scheduling algorithm to be strictly non-intrusive, a sufficient and necessary condition is that the sender's and receiver's buffers are infinite. We then show that, under the additional condition that segments are neither lost or reordered, the number of active TCP flows can be minimized by size-based schedulers, and we propose a new scheduler FAIR, which guarantees that the transfer time of every TCP flow for the origin-destination pair is reduced. We develop SCHED_TCP, a user space implementation of our scheme in order to evaluate its performance on the Internet. Our experiments illustrate the non-intrusive property of SCHED_TCP, and also illustrate that the performance gain with SCHED_TCP can be considerable. Our scheme is scalable, and it could be incrementally deployed on the Internet improving the user experience on every origin-destination pair. The main application domain of our approach correspond to situations in which there are many concurrent TCP connections within the same origin-destination pair, this might happen as a consequence of HTTP 1.1, Web 2.0 applications using AJAX (Google Maps etc.), Split TCP, Parallel Sockets, and also with the use of ChromeBook's where the user accesses to all services through the same back-end server infrastructure.