Paced Chirping: Rapid flow start with very low queuing delay

Abstract

This paper introduces a promising new direction for getting a traffic flow up to speed fast while keeping the maximum queuing delay that the new flow adds extremely low. It is therefore most interesting in environments where queue delay is already fairly low. Nonetheless, it requires no special network infrastructure, being solely delay-based, so it ought to be applicable to the general Internet. Received wisdom from TCP slow-start is that the faster a flow accelerates, the more it will overshoot the queue before the sender will notice one round trip later. The proposed technique, called paced chirping. escapes that dilemma. The sender pulses the queue increasingly rapidly with trains of packets called `chirps' that it crafts to rapidly estimate available capacity. Critically, the sender relaxes the queue between chirps, so the queue never accumulates more than a few packets. Thus, paced chirping escapes the overshoot dilemma, but still pushes enough against any pre-existing flows, so they yield their capacity. The algorithm has been implemented in Linux and shows great promise from initial evaluation. Work so far has set aside numerous issues that are all important, but not central to proving the concept, e.g. handling delayed ACKs, losses, ECN marking, reordering, variable rate links, etc, The work and the code is being published at this stage to seek review and collaboration around this promising direction.