Technology for Mortals

If you have an ISA Server between a client and a Polycom VTC unit (video teleconference), you may have some problems using some features in the Web-based administration system. For example, the dropdowns in the “Directory” may be blank. After some time on the phone with Polycom today, we found a fix.

Here’s the root cause of the problem: to retreive the contents of some of the dropdowns, there are Java applets making calls to the VTC over the Web access port (by default, port 80). The VTC unit responds back to the first request with a status 401: requires authentication. The Java applet then responds to the VTC with the username and password. When the VTC receives this, it then sends its response. Unfortunately, the VTC in this scenario has decided to not send a proper HTTP response, even though it is an HTTP request; it omits the HTTP headers! As a result, ISA server sees a “broken” response, and returns an error 500 to the requesting Java applet. The way to detect this problem, is to look at the Java console (you’ll see it in the system tray) and look for errors involving HTTP status 500.

The way to fix this is quite easy. Go to the Admin Settings of the VTC, then “Security”, and change the port that the Web Access uses (at the bottom of the screen). Then provide an access rule in ISA server (or publish it, depending upon where in your network the VTC sits in relation to the clients access it), with a new protocol on the port you used. The reason why this workaround is effective, is because ISA server is no longer treating the communications as an HTTP conversation. As such, the traffic that the Polycom unit sends which does not properly adhere to the HTTP protocol will go through smoothly.

J.Ja