Let's only consider a LTE network and there is no inter-RAT handover. I understand that a UE shall perform a initial authentication request by its serving MME during its registration. My question is, after a successful registration, will the UE periodically or randomly be requested to do another authentication or re-authentication with its serving and registered MME again? I am sure the answer should be Yes, it will be in theory. How often, however, could this happen in realities.
In accordance to https://www.keysight.com/upload/cmc_upload/All/Security_in_the_LTE-SAE_Network.PDF, the KSI_{ASME} is allocated by the MME and uniquely identifies the K_{ASME}. It is stored in the UE and serving MME together with the GUTI, if one is available, allowing the K_{ASME} to be cached and re-used during subsequent connections without re-authentication.
I dont know exactly but in general it could be based on a specific disconnection time. After which the UE might be asked to re authenticate.
In accordance to TS 23.401, the MME could request a new authentication request every TAU request.
If the integrity check of TAU Request message failed, the authentication is mandatory, otherwise is optional. The authentication functions are defined in clause 5.3.10 on "Security Function" and further information can be found on TS 33.401, as well.
About your question: if the UE is configured to generate periodic TAU, the MME could trigger the authentication procedure for each TAU.
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