Tcp Wise: One Initial Congestion Window Is Not Enough

Current TCP is very inefficient for web services. Web transactions are often very short-lived. TCP flow starts with a conservative initial congestion window (IW), which causes multiple round-trip times to finish the transmission even if the end-to-end bandwidth is sufficient for the transaction to be finished in one round-trip time. Previous research efforts have been focusing on finding the overall best IW for the entire Internet or a service company. However, we observe that one-IW-fits-all is suboptimal after one year of online measurement in Baidu, one of the top global search engine companies. To reduce the TCP latency, we propose TCP WISE, which dynamically assigns suitable IWs for different user cluster at different times on the server side. The values of users' IWs are proactively learned based on the historical experience on the server-side. Our testbed experiments show that our learning algorithm can handle the network changes and converge to the best IW. We have deployed TCP WISE in one of Baidu's production data center, and results shows that the 80th percentile latency of the HTTP responses has been reduced by 10.4% compared with current TCP with a fixed IW of 10.