Hello Experts !
I have a small question on LTE call flow, about UE attach.
My question is , towards the end of UE attach procedure, when UE sends the NAS Attach Complete message to MME, how does the eNB sends this to MME over S1 ?
Does the eNB embeds this NAS Attach Complete message inside S1 InitalContextSetupResponse message (just the same way eNB embeds the NAS Attach Request message inside S1 InitialUE message or the NAS Attach Accept message inside S1 InitialContextSetupRequest message) ?
Or is it that, for the final NAS Attach Complete message , it’s a completely separate NAS message and eNB does not embed it inside any particular S1 message. So here, UE sends the NAS Attach Complete message to eNB inside RRC ulInformationTransfer message, and eNB sends the same to MME inside S1 UplinkNASTransport message.
If the latter is true, does not it mean that, even if at MME we receive InitialContextSetupResponse from eNB, still we can not confirm that the UE is attached, until we receive the NAS Attach Accept message from eNB over a separate S1 UplinkNASTransport message?
Thank you all for your help.