To change the DSCP/ QoS values in Zoiper5 you need to open the Zoiper configuration file - "Config.xml", for editing with an XML compatible editor and search for the lines:
<signal_dscp>CS0</signal_dscp>
<media_dscp>CS0</media_dscp>
Available values:
CS0
CS1
...
CS7
AF11
AF12
AF13
AF21
AF22
AF23
AF31
AF32
AF33
AF41
AF42
AF43
EF
Windows:
Note that this option may not work on newer versions of MS Windows.
You should use policy-based QoS. For more details how to set it, please follow the provided link below:
http://technet.microsoft.com/en-us/library/dd919203%28v=ws.10%29.aspx