=====Contents=====

  * [[https://www.linuxfoundation.org/#TCP_Probe|1 TCP Probe]]
    * [[https://www.linuxfoundation.org/#Usage|1.1 Usage]]
    * [[https://www.linuxfoundation.org/#Examples|1.2 Examples]]
    * [[https://www.linuxfoundation.org/#Results|1.3 Results]]
    * [[https://www.linuxfoundation.org/#See_Also|1.4 See Also]]

====== TCP Probe======

TCP probe is a module that records the state of a TCP connection in response to incoming packets. It works by inserting a hook into the tcp_recv processing path using[[http://www-128.ibm.com/developerworks/library/l-kprobes.html?ca=dgr-lnxw961Kprobe|kprobe]] so that the congestion window and sequence number can be captured.
==== Usage====

For example, to test with iperf
<code> # modprobe tcp_probe port=5001
 # cat /proc/net/tcpprobe >/tmp/data.out &
 # pid=$!
 # iperf -c otherhost
 # kill $pid</code>

The data collected in the above example can be plotted with a simple script like
<code> #! /bin/bash
 gnuplot -persist <<EOF
 set data style linespoints
 show timestamp
 set title "$1"
 set xlabel "time (seconds)"
 set ylabel "Segments (cwnd, ssthresh)"
 plot "$1" using 1:7 title "snd_cwnd", \\
      "$1" using 1:(\$8>=2147483647 ? 0 : \$8) title "snd_ssthresh"
 EOF</code>
==== Examples====

An example is this graph created using [[https://www.linuxfoundation.org/node/add/wiki?gids[]=5066| netem ]] to emulate
a 100Mbit connection with 700ms of delay.{{https://wiki.linuxfoundation.org/images/0/05/Cubic.png?nolink|}}
==== Results====

See [[http://developer.osdl.org/shemminger/tcp|[1]]] for more TCP test results.
==== See Also====

  *  [[http://www.isi.edu/nsnam/ns|ns2]] network simulator
  *  [[http://www.web100.org|Web100 project]] instrumentation
  *  [[http://tcng.sourceforge.net/#tcsim|Tcsim]] simulate TCP under UML