Best thing while authoring test cases is predict things perfect. Meaning both positive, negative cases. If you are unable to expect the exact Expected result do mention it as TO BE DISCUSSED in the test cases.
Just need to think of all possible scenarios, think in terms of Hardware and Software context.
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Are you referring to Lab testing of DUN and NDIS? You refer to the Driver interface of Blue tooth Dial-up right?
I think you have to cover,
Installation and Un-installation testings, (use a checklist),
Test for different band widths of connections,
Negative testing wise without connection (disabling the Local Area Network Connection, known as connectionless notifications),
Test for different configurations of Hardware(RAM,Processor) and OS,