Int 6B Fn 16  - Npc Ncsi Extended Serial I/o - Log And/or Initialize Virt  [S]

   AH = 16h
   ???

Return: CF clear if successful
       AL = virtual circuit number???
   CF set on error
       ???

Note:  this function is also supported by TelAPI, which always returns CF
     clear and AL=00h

See Also: AH=11h,AH=12h,AH=17h