  Transmission Control Protocol (TCP) carries most of the traffic on the
Internet these days. There are several implementations of TCP, and the most
important difference among them is their mechanism for controlling congestion.
One of the methods for determining type of a TCP is active probing. Active
probing considers a TCP implementation as a black box, sends different streams
of data to the appropriate host. According to the response received from the
host, it figures out the type of TCP version implemented.
  TCP Behavior Inference Tool (TBIT) is an implemented tool that uses active
probing to check the running TCP on web servers. It can check several aspects
of the running TCP including initial value of congestion window, congestion
control algorithm, conformant congestion control, response to selective
acknowledgment, response to Explicit Congestion Notification (ECN) and time
wait duration. In this paper we focus on congestion control algorithm aspect of
it, explain the mechanism used by TBIT and present the results.
