Inferring client response time at the web server

Abstract

As businesses continue to grow their World Wide Web presence, it is becoming increasingly vital for them to have quantitative measures of the client perceived response times of their web services. We present Certes (CliEnt Response Time Estimated by the Server), an online server-based mechanism for web servers to measure client perceived response time, as if measured at the client. Certes is based on a model of TCP that quantifies the effect that connection drops have on perceived client response time, by using three simple server-side measurements: connection drop rate, connection accept rate and connection completion rate. The mechanism does not require modifications to http servers or web pages, does not rely on probing or third party sampling, and does not require client-side modifications or scripting. Certes can be used to measure response times for any web content, not just HTML. We have implemented Certes and compared its response time measurements with those obtained with detailed client instrumentation. Our results demonstrate that Certes provides accurate server-based measurements of client response times in HTTP 1.0/1.1 [14] environments, even with rapidly changing workloads. Certes runs online in constant time with very low overhead. It can be used at web sites and server farms to verify compliance with service level objectives.