BLT: Bi-layer tracing of HTTP and TCP/IP

We describe BLT, a tool for extracting full HTTP level as well as TCP level traces via packet monitoring. This paper presents the software architectur e that allows us to collect traces continuously, online, and at any point i n the network. The software has been used to extract extensive traces withi n AT&T WorldNet since spring 1997 as well as at AT&T Labs-Research. BLT off ers a much richer alternative to Web proxy logs, client logs, and Web serve r logs due to the accuracy of the timestamps, the level of details availabl e by considering several protocol layers (TCP/IP and HTTP events), and its non intrusive way of gathering data. Traces gathered using BLT have provide d the foundation of several Web performance studies. (C) 2000 Published by Elsevier Science B.V. All rights reserved.