LTE: Set up response

Question

I have seen that in Setup Request procedure in LTE

the response message contains

served plmnids, served group ids , and served mme codes

So it means a mme can serve multiple plmns , multiple mme groups,

but what is meaning of sending list of mme codes , because a mme is identified by group id and mme code .So ideally there should be only one mme code with which we can identify this particular mme which is responding .

So why we have multiple mme codes in response message ?

I am referring S1 Application Protocol (S1AP) (3GPP TS 36.413 version 10.9.0 Release 10).

Thanks,

SDK

Answer 1

This is related to the S1-Flex feature.

If the UE has a temporary identity, this will sent to the ENB during the RRC establishment phase.

The ENB will use the MME code present in this identity to select the MME (assuming multiple MME are connected to the same ENB) where to send the S1AP InitialUeMessage.

The point of having multiple MME identities in the same MME instance is to handle failover/loadbalancing/maintenance operations.

GUMMEIs can be moved at runtime (MME configuration update) between different MMEs in the MME pool according to the requirements.