Int 6B Fn 13  - Npc Ncsi Extended Serial I/o - Set/retrieve Request/reply  [S]

   AH = 13h
   AL = virtual circuit number
   CL = direction (00h get, nonzero set)
   ES:BX -> buffer for/containing service name

Return: ???

Note:  this function is also supported by TelAPI

See Also: AH=14h,AH=15h