The HTTP client traces were unobtrusively gathered through the use of a packet sniffing machine placed on a 10 Mb/s Ethernet segment at the head-end of the Home IP modem bank through which all IP traffic flowed (figure 1). The trace gathering program that we used was a custom HTTP module written on top of the Internet Protocol Scanning Engine (IPSE)[17]. IPSE is a user-level packet filter that runs on Linux; IPSE allows filter modules to capture TCP segments and recreate the TCP streams observed by the endpoints of the TCP connection. The custom module was therefore able to parse each HTTP request as it was happening, and write out the salient features of each HTTP request to a log file on-the-fly. Only traffic destined for port 80 was traced; all non-HTTP protocols and HTTP connections to other ports were excluded. Each user of the Home IP service is assigned a static IP address, so we could track individual users over the entire duration of the tracing experiment.