R8-UE request CSFB service in LTE cell enabled flash CSFB based on RIM

Hi all experts,

Flash CSFB based on RIM feature has benefit of reducing CSFB setup time, this is due to RRC-conn-release message that enb sent to UE also contain PSC + SI of UMTS cell.
This feature require enb/CN and UE support R9 and later.
Have anyone ever seen how a R8-UE request CSFB service in a LTE cell enabled flash CSFB?

  • CSFB will be failed.
  • or enb checked UE capability and just send UMTS-frequency only to UE and UE continue with normal CSFB

2019 I saw many cases where flash csfb was zero. and S1 was R8. …
today I was checking the same but to my surprise… I have sites (many . like 1k) with R8 and flash csfb happening (?) unfortunately Im overloaded with bureaucracy enough to investigate interesting matters but if I find time I would lalso ike to know how is that possible…

R8 MME/SGSN can not support flash CSFB, at least R9.
Can you check: DSP UTRANRIM, DSP S1INTERFACE to check whether enb can obtain UTRAN SI and which version of core network?

yes, my mistake. checked again. there was 2 S1 created. one was R8 for another CN operator… so my dynamic table was bugged.(that is what happens when you check thousands elements on a hurry hahah! ) As we know, R8 is not having flash csfb…
on the other hand. the best proof that it is working (through redirection) is that we dont receive complains… customers were very sensible to this problem in the last years.

site with no FLASH:

Second option!

Hello All.

How to confirm if RIM feature enabled is working in flash CSFB?

In LTE rrcconnectionrelease msg, check r9 message, it consists of details if cells on which it is supposed to CSFB i.e. UARFCDL and PSC, ARFCN in case if 2G

If nothing appears in r9 then RIM is not enabled.

There is switch with name UTRAN or GERAN RIM switch.

Also if this switch is enabled and still zero CSFB attempts than check eNACC switch at 2G end.

CSFB attempts are there but failing at 2G/3G end.

2G is actually Huawei.

Anything to configure in Huawei?

Check how the Huawei 2G cell is configured in the LTE side.

Yes it’s added in ADJG & LNRELG.

Check eNACC switch at 2G end.

Sometimes it fails when the BCCH, LAC or cell id is wrongly configured.

Everything checked, and are correct.

Actually there is some licence issue also in LTE reselection in Huawei as well.

How to assign priority to the adjacent target cells?

Check blind priority.