Number of TCH (in HR or FR usage) drops due to BSS problem during any TCH handover preparation and execution phases.
This counter is incremented on the cell on which the problem occurs(In the case of internal inter-cell handovers, it is not incremented on both serving and target cell). For problems that are not related to a specific cell, the counter related to the serving cell will be incremented.
It may happen that several causes of failures mentioned below are detected consecutively. In that case, the counter will only be incremented once, as soon as the handover procedure fails.