XCP vs. CUBIC with Quick-Start: Observations on Implicit vs. Explicit Feedback for Congestion Control

Congestion control in transport protocols can be performed implicit when packets are lost, or explicit with feedback from the network. In this paper we compare some aspects of implicit and explicit congestion control using a variant of CUBIC with Quick-Start, called CUBIQ. We compare CUBIQ with regular TCP, XCP and CUBIC, and find that CUBIQ performs as well as XCP in most cases, and much better than XCP when XCP is hampered by small buffers in large BDP-networks. These results indicate that the feedback provided by Quick-Start may be enough for a sender when it needs to find the right transmission rate, also in the initial phase of a communication.