why AgBr is a common example of frenkel and schottky defect?

Schottky defect is observed in crystals having high coordination number and in which anion and cation have similar sizes.  Frenkel defect is observed in those crystals where there is large difference in size of cation and anion so that either cation or anion (generally smaller in size) can move into the interstitial site. Thus Frenkel defect is vacancy defect at that point from which anion or cation is replaced and interstitial defect where it is placed.

In AgBr, Ag+ ion is small in size and when removed from lattice point they can occupy interstitial site and therefore show both frenkel and schottky defect.