Hi Experts.
Does anyone faced Attach Reject with cause No suitable cell in Tracking Area?
Yes,it could have different reasons.
Any specific?
Issue in Core?
It was working fine in the past.
Authentication issue, IMEI issue or ban TAC for specific PLMN. And could have this cause according to MME configuration.
Whether observed for a particular UE?
Thanks 
No, all UEs
Most of the time it’s bcos TAC is prohibited in MME.
We recently faced this issue when by mistake a core guy blacklisted a TAC in MME.
So:
Either in LTE or 5G NR, if UE receives attach reject/registration reject from cell1 with cause ‘no suitable cells in tracking area’.
UE attempts attach/registration to cell2 with different tracking area.
Is the understanding correct?
Yes, UE behavior will change according to rejection cause and for no suitable cell in tracking area, it will try cell with different TAC if exists.
Thank you!
In case if a cell with different TAC doesn’t exist what could be UE behaviour?
Will it try to different RAT?
Yes, correct.
I think it depends on rejection cause/code.
It will not try another RAT if for example rejection cause is “PLMN not allowed”.
Got it.
Here cause is’ no suitable cells in tracking area’.
Testplan says cell rejects attach attempt with above cause.
But later it successfuly attaches to same cell.
That’s creating confusion.
Hi Dears.
Anyone has faced to 2G -4G cell reselection issues with MME sending TAU reject with cause “no suitable cells in tracking area”?
We do have 2G LAC-RAC definitions in SGSN present, still we have this problem ongoing.
2G-4G reselection will have only when 4G TAC will be geographic part 2G LAC and as per reason you posted above indicate that serving 2G cell and nearby 4G cell where reselection rejected.
We have 4G TAC and 3G LAC mapped.
Is it possible to map 1 TAC with 2 LACs (3G and 2G)?
No, a TAC can be mapped to a single LAC either 3G or 2G.
So how do we resolve the issue?
Anyone has any suggestion for MME configuration?