PPT Slide
The bands of stacking faults form a configuration resembling steps on a stairway.
These steps are barriers to further slip on the atomic planes involved, as well as in the adjacent planes.
The dislocation is sessile because its Burgers vector does not lie in either of the planes of its stacking faults.
However, it is not a true sessile dislocation in the sense of the Frank partial because it is not an imperfect dislocation.