TRAIN        TRAIN        TRAIN          TRAIN
STATION A    STATION B    STATION C      STATION X
+--------+   +--------+   +--------+     +--------+
|WIFI AP1|   |WIFI AP2|   |WIFI AP3|     |WIFI APX|
|        |   |        |   |        |     |        |
+--------+   +--------+   +--------+ ... +--------+

     TRAIN WIFI CLIENT
        +--------+
+---------------------------------------------->