This exercise is based on an exercise that came with the B.E.R.P. (Buzz Extension and Resistance Piece) and is designed by the Los Angeles trumpeter Mario Guarneri. You can also use a similar device, called BuzzAid.
An exercise, using glissando can also be found in the "Allen Vizzutis books" and in "Brass Tactics" by Chase Sanborn.
The range is from the center note G in the staff, one octave up and one octave down. Try to find the starting pitch without any helping instrument (piano) - then check it. This will train the ear and the "muscle memory" of the starting note G (concert F).
An important goal in this exercise is to use a lot of air support. Play strong and try to make the sound very clean.