+------+  +-----+                                 |                                         +------+  +-----+
    | PROBE|  | IDS |                                 |                                         | PROBE|  | IDS |
    +-+----+  +--+--+                                 |                                         +-+----+  +--+--+
      |          |                                    |                                           |          |
      |  +-------+                                    |                                           |  +-------+
      |  |                                            |                                           |  |     
    +-+--+-+                                          |                                         +-+--+-+          
    | HUB  |                                          |                                         | HUB  |    
    +--+---+                                          |                                         +--+---+ 
       |                      site 1                  |                       site 2               |
       |                                              |                                            |
       |                                                                                           |                              
   +---+----+  trunk +------+      FE0/1+------+G0/1   G0/1+------+FE0/1    +------+  trunk   +----+---+ 
   |sw-PAN-1+--------+sw-1a |-----------| SWi1 |-----------| swi2 |---------|sw-2a +----------+sw-PAN-2|
   +--+-----+        +--+---+           +------+           +------+         +--+---+          +----+---+
      |trunk      trunk |FE0/24                                                |FE0/24 Trunk       |trunk
      |                 |                                                      |                   |
      |                 |                                                      |                   |
      |                 |                                                      |                   |
      |                 |                                                      |                   |
      |                 |                                                      |                   |
      |                 |                                                      |                   |
      |                 |                                                      |                   |
      |                 |                                                      |                   |
      |                 |                                                      |                   |
      |           trunk |FE0/24                                                |FE0/24 trunk       |
      |              +--+---+      FE0/1+------+G0/1   G0/1+------+FE0/1    +--+---+               |
      +--------------+sw-3a |-----------| SWi1 |-----------| swi2 |---------|sw-4a +---------------+
               trunk +------+           +------+           +------+         +---+--+trunk
                                                     |
                                                     |
                                                     |
                                                     |