Abstract

Why does it take so long to download a Web page from a Web server? We analyze the download latency for pages for a variety of situations, in which Web browser and server are both within the same country as well as in different countries. Our study examines several sources of latency in accessing Web pages: DNS, TCP, the Web server itself, and the network links and routers. We divide the total download time into four parts: DNS query, connection setup time, time to get the first byte of a Web page, and downloading time. In most cases, roughly half of the time is spent from the moment the browser sends the acknowledgement completing the TCP connection establishment until the first packet containing page content arrives. The bulk of this time is the round trip delay, and only a tiny portion is delay at the server. This implies that the bottleneck in accessing pages over the Internet is due to the Internet itself, and not the server speed (as suggested by another study). The second bottleneck is the 3-way TCP connection establishment (consuming 1/5 to 1/4 of the delay). Conclusions are drawn on how to decrease latency.

Citations