Systematic performance and robustness testing of transport protocols with congestion control

Many modern variations of transport protocols are equipped with improved congestion control algorithms that are more proactive rather than reactive to congestion. Consequently it is expected that they will rarely need to invoke loss recovery mechanisms (namely abrupt reduction in transmission rate and timeout intervals). Therefore unlike congestion control algorithms, the loss recovery mechanisms have undergone little or no change as the Internet has evolved and scaled up in terms of dimension, traffic and bandwidth.;There is however insufficient insight regarding worst-case performance and robustness of transport protocols with congestion control under severe congestion conditions when even the tightest and most-enhanced congestion control mechanisms fail to prevent severe congestion leading to packet drops and are thus forced to invoke their legacy loss recovery mechanisms.;We develop a systematic framework to test performance and robustness of transport protocols with congestion control by creating severe congestion scenarios that (a) stress these protocols and expose performance vulnerabilities and robustness issues of their congestion control and loss recovery mechanisms, (b) identify and highlight harmful side effects of employing certain scheduling, active queue management (AQM) and routing techniques along with these protocols, (c) serve as a benchmark for non-malicious worst-case performance analysis in order to identify unintentional occurrences of our scenarios in networks and, (d) virtually make an ideal Denial of Service (DoS) or Distributed Denial of Service (DDoS) attack scenario, since they are inherently more difficult to detect.;Using our systematic framework at the flow-level, we define and model our severe congestion scenarios in terms of scaling, temporal and spatial parameters of the flows involved in the scenario.;Our main case-studies include several variants of TCP and a promisingly-efficient and TCP-friendly transport protocol for high bandwidth delay environments: eXplicit Congestion Protocol (XCP). In conclusion, our study exposes vulnerabilities of rate-adjustments rules used in congestion control mechanisms of these protocols and provides systematic ways to exploit their vulnerabilities to invoke the protocols' loss recovery mechanisms repeatedly. We verify our findings by studying our severe congestion scenarios in a packet-level simulation platform and running test-bed experiments.