Error connecting to KNX bus: The serial FT1.2 KNX connection requires the RXTX libraries to be available, but they could not be found!

Add-ons Bindings
1

I tried to switch from eibd to the KNX-binding internal KNX communication. I’ve configured a udev-rule for my USB interface which creates a link to /dev/knxd which is owned by openhab user. In service/knx.cfg is this line without any ip-definition:

serialPort=/dev/knxd

I deleted the knx configuration in karaf by

config:delete org.openhab.knx

and restarted openhab2.
Unfortunately I’m not lucky with this, as I alwasys get this error lines

2017-03-15 16:42:54.950 [ERROR] [nx.internal.connection.KNXConnection] - Error connecting to KNX bus: The serial FT1.2 KNX connection requires the RXTX libraries to be available, but they could not be found!
2017-03-15 16:42:54.951 [WARN ] [nx.internal.connection.KNXConnection] - Initial connection to KNX bus failed!

Seems there is something missing, but how can i load or install this?