Although the method appears to be implemented on WM5.0 and above, no device which implements it has yet been found. On Peter's iMate JasJar it returns error code 0x00000490, which apparently represents "Element not found".

The NotSupportedException occurs when the function returns an error code, and is due to the method not being implemented on the local device side, rather than being an issue with the remote device. The original error code can be retrieved from the inner exception which is of type Win32Exception. See the source to the SdpBrowserPPC sample for an example, it produces output like the following:

CopyC#

Failed retrieving Rssi (NotSupportedException)
>> Win32Exception (Win32Exception)
     NativeErrorCode: 1168 (0x490)

If the method is not present at all (e.g. on older devices) it will throw a PlatformNotSupportedException. The method is only implemented in order to support newer devices which will hopefully correctly implement the method and return a valid RSSI value.