...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
             |<======================================>|
             |                   L                    |
...=========>|<==================><==================>|<==========...
             |         L/2                L/2         |
             |<=><===>|                      |<===><=>|
               m   d  |                      |  d   m
                      |<====================>|
                    available counting interval