An Empirical Study of the Effectiveness of Fallback on the ECN

ECN (Explicit Congestion Notification), as an effec¬tive approach for TCP congestion control, has been proposed for many years. However, the current network environment cannot provide particularly good support for ECN, so its deployment is much lower than expected. In order to bring the advantages of ECN into full play, a mechanism called Fallback is introduced to solve the problem that connection cannot be established after enabling ECN by default setting. In this paper, we evaluate the effectiveness of Fallback by using the data set of web domains as the test servers provided by Alexa. For the same test server, we first negotiate a connection with Not-ECN-Capable, and then negotiate a connection with ECN-Capable, if the sender does not receive the response to ECN-Capable negotiation from the receiver by the end of timeout, it will enter the Fallback state, and switch to negotiating a connection with Not-ECN-Capable. By extracting the header fields of the TCP/IP packets, we have found that the rates of Fallback are a bit different among the domains, the effectiveness of Fallback is shown on the low side, and the value of initial RTO (Retransmission Timeout) has a strong impact on Fallback.