Cisco IP Phone Image File - Blank Image

Version 1
    This document was generated from CDN thread

    Created by: Rand Dusing on 25-06-2009 03:00:36 PM
    I'm experiencing an issue on a wide variety of Cisco IP Phones.  Sometimes when the phone receives an CiscoIPPhoneImageFile, the screen just displays grey where the image would be.
    I thought it may be corruption from my server, but my server is sending the same packets over and over again.  Something could still get corrupted after leaving the server, but isn't TCP suppose to correct for that?
    My co-worker and I ran some trials.  We each ran the service and counted the number of times a blank image showed up out of one hundred refreshes.  We ran three trials to make it a little more accurate.  His 7975 had about an ~84% success rate while my 7971 was close to a ~98% success rate.
    Next we switched phones to try to rule out any network issues.  After moving phones and restarting them, all our trials came back as 100%.  Since then I've been running the program off an on for long periods and haven't seen any more "dropped" images.  This leads me to believe that Cisco IP Phone itself is the cause of the problem.  Perhaps the phone's memory is filling up, and it must be restarted every so often to fix the issue?
    Once the grey images return, I'll restart my phone again and see if it fixes the issue.
    Does anyone have any insight onto why this happening?

    Subject: RE: Cisco IP Phone Image File - Blank Image
    Replied by: David Staudt on 25-06-2009 09:04:45 PM
    The phones do have limited resources, and I have seen situations where rapid XML object refreshes can exhaust the available TCP ports the phone can handle.  When the phone makes a GET request, it always uses HTTP connection-close, and so the standard TCP port timeouts must occur before the port can be reused.  Since CiscoIPPhoneImage results in two requests (one for the XML, another for the .png file) I would expect port exhaustion might happen twice as fast.
    If you look at a Wireshark packet capture of this, you would see the phone just not making a TCP/HTTP connection when the page should be getting requested.

    Subject: RE: Cisco IP Phone Image File - Blank Image
    Replied by: Rand Dusing on 29-06-2009 06:54:53 PM
    We are going to set up a lab and monitor the lines to see if the phone is even requesting the PNG after successfully downloading the XML.  Hopefully this will show where the problem is coming from.  Unfortunately it sounds like we wouldn't be able to fix the problem even if we figure out what's causing it.