ATTACH COMPLETE is sent in response to ATTACH ACCEPT message.
This message will be sent by UE to Network.
Attach Complete is piggy backed with RRC Connection Reconfiguration Complete.
The total RRC Connection Reconfiguration Complete message will consist of:
RRC : RRC Connection Reconfiguration Complete + NAS : AttachComplete + ESM : Activate Default EPS Bearer Context Accept
So from the above line we can see that Attach Accept is combined with Activate Default EPS Bearer Context Accept message.
The ESM sub layer of the UE will check if the default EPS bearer context has been activated, the UE will send Attach Complete message along with Activate Default EPS Bearer Context Accept message.
It will be sent in “ESM message container” IE to the network.
If there is an error in UE’s ESM layer, then UE will send Detach Request.
The IE’s present in Attach Complete are:
Attach complete message identity
ESM message container
Reference: 3GPP TS 24.301
