LTE: Attach Complete

The ATTACH COMPLETE message is sent by the UE to the network in response to an ATTACH ACCEPT message

When the UE receives the ATTACH ACCEPT message combined with the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message, it shall forward the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message to the ESM sublayer. Once the ESM sublayer indicates that the default EPS bearer context has been activated, the UE shall send an ATTACH COMPLETE message together with an ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message contained in the ESM message container IE to the network

If the ACTIVATE DEFAULT BEARER CONTEXT REQUEST message combined with the ATTACH ACCEPT is not accepted by the UE due to failure in the UE's ESM sublayer, then the UE shall not send ATTACH COMPLETE message. Instead, it shall initiate the detach procedure by sending a DETACH REQUEST message to the network. Further UE's behavior is implementation specific

Reference: 3GPP TS 24.301

Example: ATTACH COMPLETE Message