I get a message Unable to start V*CALL just after having changed the IP address in V*CALL Config what can I do ?

Wait a few seconds for the service to restart, then try again!

The Send vu-meter indicates that a return signal is present, but I cant cue anything...

If you have only one single sound card on your system, the I/Os have been configured during the installation process for the physical output of the codec, therefore you cannot set a Cue audio resource. To enable the Cue feature, you need a second audio device.

My status LED has turned red even though the measured values seem to be okay (CPU, jitter, loss). What happened?

The CPU value displayed being an instantaneous one, it is probable that this value has temporarily passed the threshold of 80%.
To refresh the LED display, click onto it.

I use an RTP stream as source to be sent; if I stop the source, then re-start it, I dont have any signal in V*CALL. What happens?

V*CALL is still waiting for packets from the previous RTP session, therefore youll have to re-connect V*CALL to have it detect the new session.

Note: in case you have just unplugged the network cable, V*CALL will continue once you have re-plugged the cable as the RTP session itself has not changed.

I encounter drop-outs in my audio streams that I cannot explain, where do they come from?

Your computer probably runs a device driver that does not conform to DPC routine management specifications.
We suggest to check whether this is the case for your computer.
A tool you might use is, e.g., DPCLAT (DPC Latency Checker). For more information please refer to www.thesycon.de/eng/latency_check.shtml.

I have correctly configured V*CALL, established my connection, but I cannot hear the participant. Where is the problem?

The Windows default audio device is used by default for ringing/signalling. Make sure this device is NOT IDENTICAL with the one defined for the Return audio ressource; otherwise you will either not have audible notifications, or you may not be capable of hearing the participant. You may also disable the ringing feature by creating a text file in the VCALL.exe folder: name it "VCALL.xml" and insert the lines:

V*CALL - and V*CALL Config - take ages at start-up; the system seems to be busy, what is it doing?

There are two possible reasons for this behaviour:

1. You have installed and been using V*CALL with an evaluation license, and this temporary license has now expired.

To check whether this is the case, launch


to check the license validity.

2. V*CALL is an application based on Microsoft WPF that accesses http://crl.microsoft.com. In case your http proxy is poorly configured, the application may need more than a minute before it is up and running. crl.microsoft.com is Microsofts certificate authority server (CRL stands for Certificate Revocation List), used to verify whether the certificate for an application (or website) is legitimate or not.

You can either configure your http proxy through V*CALL Config to ensure fast access to the above-mentioned Microsoft web site, or you can workaround and prevent your applications all of your applications! to connect to the corresponding Microsoft server. To do so,

go to IE, select Tools|Internet Options|Advanced

Uncheck Check publishers certificate revocation on the security tab.


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