Recurring TAU problem

4G LTE
1

In our tests with General Mobile GM8, and Xiaomi Mi11 T model UEs, it was observed that there was constant TAU ​​(every 10 seconds) due to “Combined TA/LA updating with IMSI attach” cause. In MME, periodic TAU value is set as 1200. What do you think could be the reason for this problem? Thanks a lot.

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2

Hi bro, so whats the test you are running ?and the conditions so we can understand.

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If it is not due to t3212 for periodic tau, check the CA and mimo configuration.
For test, please deactive CA, and test , then share the result.
I suppose this case is happen when CA is activated blindly.

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4

Hi Ramin, Thank you very much for your answer, I didn’t quite understand what you meant by CA. Do you mean Carrier Aggregation? I’m asking because I’m a Core Network engineer and I don’t know RAN as much as you do. Is there such a parameter in 4G RAN? Do you also mean 4G mimo configuration? By the way our RAN and Core is only 4G.
Best regards.

5

Hi Sir, Many thanks for your quick reply. We are trying to perform basic acceptance tests such as simple IMSI detach and volte in the 4G environment, but TAU ​​constantly occurs in the system due to a situation we do not know why. If you want a more detailed log, I can share it. I thought if anyone had experience like this before it might help. It’s not due to T3412 timer, there should be sht problematic (may be at RAN side parameters.)

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Hi brother, yes in ran side, there is parameter for this case. Better to ask ran npo team to disable carrier aggregation/ change the CA policy to measurement based.

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Many thanks Ramin, We will try, then I will inform you.
Best regards.

8

so TAU happens because you change of TAC and also because of a periodic timer as stated in the chat, so while doing your tests are you changing froum one cell to another? because if this happens and the cells dont have the same TAC the TAU will happen. Now as Ramin says, if you are testing many scenarios as using Carrier Aggregation the cells may or not have a different TAC.
So if you checked the timer already now check the TAC defined for the cells you are testing and compare TAC.

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9

I checked the timer, it’s ok. TAC of both gNB’s are the same, so there is no TAC change. We will follow Ramin’s instructions about CA, then I will inform you again. Many thanks for your help.
Best regards.

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