EMM cause (LTE NAS)3GPP TS 24.301 §9.9.3.9 and Annex A
What it means
Network failure: a failure inside the network not caused by the subscriber, e.g. the MME got no answer from the HSS.
Where you see it
In LTE NAS Attach reject, Tracking area update reject, Service reject or Detach request.
What to check
Check the MME's interfaces (S6a towards the HSS, S11 towards the SGW) at the time of the reject.
Look at the S6a (MME↔HSS) and S11 messages just before the reject: they usually show the real trigger.
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