DCP-EW: Distributed Congestion-Control Protocol for Encrypted Wireless Networks

Abstract

Recently, Variable-structure Congestion-control Protocol (VCP) has emerged as a great practical alternative of deployment for congestion control by requiring the use of only two ECN bits in the IP header. However, VCP suffers from a relatively low speed of convergence and exhibits biased fairness in moderate bandwidth high delay networks due to utilizing an insufficient amount of congestion feedback. Our previous work Double-Packet Congestion-control Protocol (DPCP) addressed this problem by increasing the amount of the feedback distributed over two ECN bits in the IP header of a pair of packets. However, DPCP faces deployment obstacles in encrypted wireless networks due to the fact that it relies on partial information in the TCP header and the TCP header information is lost when crossing encryption boundaries. Furthermore, wireless networks are characterized by both error- and congestion-caused loss. Our previous work has revealed that the efficiency of DPCP, and for that matter any congestion control protocol, over wireless networks may be reduced as the result of not being able to differentiate between two types of loss. In this paper, we propose an alternative congestion control protocol to which we refer as Distributed Congestion-control Protocol for Encrypted Wireless (DCP-EW) networks. DCP-EW is capable of efficiently operating in encrypted wireless networks while preserving all of the benefits of DPCP for wired networks. It does so by passively utilizing the IP Identification field of a packet header instead of the TCP header in conjunction with a heuristic algorithm to differentiate between different sources of loss. We implement DCP-EW in NS-2 and the Linux Kernel. We demonstrate the performance improvements of DCP-EW compared to DPCP and VCP through simulation and experimental studies.