Sonar User Guide

How it works

Sonar is a web page with some clever JavaScript code that sends a packet with unique characteristics when the user clicks on a button.

Sonar screenshot

Above we see the marker page after clicking on Send Marker; the details of the marker are logged on the page.  The marker is easy to spot in a network trace.

Marker trace entries

Of course, the GET request may be rejected with an error code but that doesn't matter because we have the marker we need.  Note how the Info field shows:

  • The text that was appended to the marker url; slow_outlook
  • The username value; matthew
  • Details of the marker number; m=1
  • A Universal Unique Identifier (UUID); a599d22a-8733-4cf9-9511-738a18dbdd57

Clicking the Send Marker again send another marker:

Trace Marker screenshot showing the second marker

We can see that the new marker appears in the log.  A quick look at the trace and we see the matching entry:

Wireshark screenshot showing the second marker on the wire

Note that the identifier data is the same as the earlier marker but this one shows as m=2, matching the marker in the Sonar log.

What if we want to send a marker targeting a server that is not running a web service?  We'll see later that Sonar can send markers targeting any service.