How often eNodeB request the SI (System Information) of the target cell (2G/3G)?

RAN
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RAN Information Management(RIM) for SI Tunneling

For the Redirect with System Information feature to function properly, the system information for the target cell must be accessible to the eNodeB.

The eNodeB requests system information from the target cells using RAN Information Management and this feature must be supported by the target RAT. This requires that the RAN Information Management Network Assisted Cell Change (NACC) Packet Data Unit (PDU) is used for retrieving system information from GSM, WCDMA target cells.

Question is how often eNodeB request the SI of the target cell(2G/3G)? At the time of CSFB only? If it is stored in MME, how often it is updated in MME?

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As per my understanding, we should visualise RIM status as association between eNB & WCDMA or GSM cell.
Each inter-RAT neighbour relationship have a RIM associaiton status which can be one of

  1. disabled
  2. available
  3. unavailable.
    If RIM association status is available, eNB would be able to provide SI via RIM in the redirect message.
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For Huawei eNB, it is default periodicity to query RIM of 2G/3G.

I remember it will request in 3:AM everyday and repeat 4 hours.