Thanks for your help.
I found bellow description which can be useful for others, so I share with you:
in 3.1.12.1 of TS 48008. Brief description of the algorithm is provided as follows:
1. A total of 15 flow control levels are available.
2. The MSC first starts T5 (30s). In the period specified by T5, the system does not change the flow control level. After T5 expires, the system starts T6 (also 30s).
3. In the period specified by T6, if the system receives an Overload message again, it decreases the flow control level by 1 and restarts T5. If T6 also expires, the system increases the flow control level by 1 and restarts T5.
4. The preceding steps occur alternatively. To prevent restriction of all services, level 1 is set as the lowest flow control level. When the flow control level increases to level 15, the system ends flow control.
The flow control algorithm aims to protect the BSC against soaring traffic
Br,
Mahmoud