Distributed ECN-Based Congestion Control

Following the design philosophy of XCP, VCP is a router-assisted congestion protocol that intends to balance the efficiency and the fairness control in high Bandwidth-Delay Product networks. While both VCP and XCP achieve comparable performance, VCP represents a more practical alternative of deployment as it only requires the use of two ECN bits in the IP header. However, the use of two ECN bits only allows for establishing three levels of congestion notification signaling. Our previous work reveals that VCP suffers from relatively low speed of convergence and exhibits a biased fairness behavior in moderate bandwidth high delay networks due to utilizing an insufficient amount of congestion feedback. In this paper, we propose a distributed ECN-based congestion control protocol to which we refer as Double-Packet Congestion Control Protocol (DPCP). DPCP is capable of relaying a more precise congestion feedback compared to earlier proposed Variable-structure Congestion-control Protocol (VCP) yet preserving the utilization of the two ECN bits. By distributing (extracting) congestion related information into (from) a series of packets, DPCP is able to circumvent the limitations of VCP related to the use of three congestion levels encoded into two ECN bits. We implement DPCP in Linux and demonstrate its performance improvements compared to VCP through experimental studies.