Operation of netmon:

If netmon detectes a object is not responding
it will do the following:
  * set 'Alive/Dead' flag in TAGS field in interface table
    of object.

  - Generate a trap and send it to trapd.

  - PROBABLY NOT
    Generate a signal to upper API layer.
    This signal is received by main gxsnmp
    program, which will update its graphical display
    of the object if any.
