Adjustable, Delay-based Congestion Control in a Reliable Transport Protocol over UDP

Abstract: Hosts in the peer-to-peer networks need to communicate to each other directly, but majority of nodes in the Internet are private nodes, that is they are behind Network Address Translators(NAT), and cannot be reached directly like a public node. Therefore, NAT traversal techniques are required to enable nodes to make end-to-end connections. These techniques seems to be more effective over UDP transport compared to TCP. However, standard UDP lacks some useful features, such as reliability and in-order delivery of packets. It also does not have congestion control mechanism to prevent congestion in the links. In this protocol, named RABAT, we are going to present a transport library over UDP for peer-to-peer applications that provides a delay-based congestion control mechanism and also in-order delivery of packets. Our congestion control mechanism is derived from LEDBAT draft [8] and reliability implementation is based on standard TCP. RABAT provides both intra- and inter-protocol fairness, which in case of the latter is back-off to TCP. The protocol also enables users to change priority of the running transports at runtime. To the best of our knowledge, this is the first open-source implementation of LEDBAT in java.