State of knowledge

December 2020


Yealink devices cannot be used from the home office. The phones can register with the uaCSTA server, but do not transfer line information. 

To the best of our knowledge, this behavior currently only occurs in connection with Yealink end devices. 

Possible reasons

An unset registry key in the Windows registry database. The port number for the public interface is assigned under HKEY_LOCAL_MACHINE (HKLM) → Software → ESTOS → uaCSTAServer in the PhoneWANPublicPort entry. However, this is always set to 0.
Thus, the uaCSTA accesses an interface which has already stored valid port information. In this case the internal interface. This is used to pass a wrong IP address to the device, so that it has no possibility to communicate with the uaCSTA server after registration.


You can set the registry entry/registry key manually. To do this, go to the registry and navigate to the entry. "HKLM → Software → ESTOS → uaCSTAServer". Replace the 0 in the entry "PhoneWANPublicPort" with the corresponding port from the uaCSTA server settings.


A version with the solution to the problem is available from version 6.02.