Illustration of the in phase oscillation of different loop segments. The 171 Å image of the active region NOAA 11650 taken on 5 January 2015 00:20:12 UT is presented in the left panel. The oscillated loop is highlighted with a dotted line. Bold white lines show three slits used for constructing time-distance plots. The time-distance plots for three different positions are shown in the right panel. One oscillation cycle is indicated with white vertical lines.