How to make forwarding of external lines when the internal number is not answered?

Question

URL Handling

Good time colleagues.
Please advise how to accomplish the following task.
1 - a call from an external line comes to the extension number - 101 and if the extension number 101 is busy or does not answer within 3 rings, the call is forwarded to the number 102 (I implemented this), but item 2 must also be implemented
2 - making calls on the first item is not Calls from internal numbers should be forwarded. Those. for internal numbers, call forwarding must be disabled.