i went to tunis several times, for tunisana and tunisie telecom too… 😉
ho failure due to congestion means :
1/ the BSC detects that 1 call shall do a HO.
2/ the BSC evaluates what would be the best candidate for this HO
3/the BSC detects this candidate is congested.
In these 3 steps there were NO message sent (no msg to BTS, no msg to MS, no msg to MSC). It is all internal.
The BSC will then look for the 2nd best candidate, and so on. If 2nd is not congested, then the HO Execution is performed.
After T7 seconds, if HO preparation is still ongoing, then the list of “congesteed” cells is reset. The best candidate will be attempted again.
The “request” is not queued at all. The only queuing is done for incoming EXTERNAL HO (means : coming from a different BSC). In this case, the incoming HO request is queued for T_QHO – IF THE TARGET CELL IS CONGESTED. At T QHO expiry, the target BSC will reply to the serving BSC, saying the target cell is congested.
During T QHO, the serving BSC just waits….