Cisco Unified Communications Manager (CallManager)

VT Advantage: Troubleshoot Video Problems with Traces

Document ID: 50345

Updated: Nov 17, 2005



If your initial efforts to troubleshoot are not successful, you could be required to use traces. This allows you to analyze what component has failed with Cisco VT Advantage. This document discusses the use of trace tools provided with Cisco VT Advantage and how to understand them.



Readers of this document should have knowledge of these topics:

  • A comfortable understanding of how to read and interpret trace output from the Cisco CallManager and Cisco VT Advantage

Components Used

The information in this document is based on these software and hardware versions:

  • Cisco VT Advantage used with Microsoft Windows 2000 and Windows XP

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.


For more information on document conventions, refer to the Cisco Technical Tips Conventions.

How to View and Understand CAST Traces

These sections provide information to help you view and interpret CAST traces.

View the CAST Trace

From the Start menu, open the Cisco VT Advantage Diagnostics window. As shown in Figure 1, there are three buttons, labeled Update Status, CDP Viewer, and CAST Viewer, at roughly 6:00 in this dialog box:

Figure 1 – Diagnostics Window


The CAST Viewer Dialog Box

If you press the CAST Viewer button, a dialog box appears. You can use this box in order to view what Cisco CallManager sends. Figure 2 is an example of the CAST Viewer dialog box you see.

Figure 2 – CAST Viewer Dialog Box


There is a great deal of information in this dialog box. However, in order to track your video call, you really only need to examine the trace messages. Here is some information to help you troubleshoot your video problem with the CAST Viewer dialog box:

  • On the right-hand side of the dialog box, you see a list of messages that are exchanged between Cisco VT Advantage and the Cisco CallManager. If you use your mouse in order to select one of the messages, the detail in the Message Breakdown window expands on the right-hand side as well (see Figure 3).

    Note: There are a series of messages, all around 12:52. There is a long series of call status messages that are sent while the call is set up. These let Cisco VT Advantage know what state the phone is in at any given time.

    Note: Although these messages provide additional information, all you really need to examine is the message highlighted in Figure 2. The OpenMultiMediaReceiveChannel message is sent by the Cisco CallManager in order to indicate that a video stream is going to be sent to the PC.

  • If you see the OpenMultiMediaReceiveChannel message, a corresponding acknowledgment sent by Cisco VT Advantage is visible. If you do not see this message, no video was sent and none is expected.

  • The Cisco CallManager also sends a command that tells Cisco VT Advantage to send video. This comes in the form of a StartMultimediaTransmission message, which tells Cisco VT Advantage to begin video transmission. Without this message, no video is sent.

  • You can bring up the CAST Viewer dialog box at any time, and this dialog box shows you a trace of the messages that were sent during your call. You can also save the contents of the message buffer to a file for later analysis or in order to help Cisco Technical Support troubleshoot your video issues.

Understand CAST Messages

If video was not enabled with your call, look at the CAST Viewer first. This example has a sequence of station information messages, but no commands to send or receive multimedia data. What does a message buffer, such as the one in Figure 3, mean?

Figure 3– CAST Messages


If you see a sequence of station information messages but no commands to send or receive multimedia data, for some reason the Cisco CallManager decided this was not a video call. There are a number of possible reasons for this:

  • The remote end did not report that the call is video enabled.

  • The remote end is video enabled, but you do not have a compatible set of coder-decoders (codecs).

  • The remote end is video enabled, but needed conference resources are unavailable.

All of these are possibilities. More often than not, if you see the CAST messages and do not see any messages that ask to initiate video transmission, there is nothing wrong. Most likely, the Cisco CallManager decided for legitimate reasons not to use video on the call.

Related Information

Updated: Nov 17, 2005
Document ID: 50345