The options are:
Acknowledge and discard: Acknowledge Reset Request packet and discard it.
Disconnect: Causes a Clear Request packet to be sent to remote host.
For expedited data, the menu options are defined as follows:
Acknowledge and discard: Acknowledge expedited data and discard it.
Disconnect: Disconnect connection in response to expedited data.
Reset connection: Reset connection in response to expedited data.
To restrict access, adding a measure of security, you can choose not to accept calls from unknown hosts, that is hosts who addresses are not in the Remote Host to X.25 Address Map.