LTE: Attach Accept

The ATTACH ACCEPT message is sent by the network to the UE to indicate that the corresponding ATTACH REQUEST has been accepted. Typically, the ATTACH ACCEPT message is piggy-backed on RRC CONNECTION RECONFIGURATION message

The result of the EPS attach is indicated in the IE EPS Attach Result. The result can be either “EPS only” or “combined EPS/IMSI attach”. The result "combined EPS/IMSI attach" indicates that the attach request for EPS and non-EPS services, or for EPS services and "SMS only" have been successful. The result "EPS only" indicates that the attach request for EPS services (only) has been successful but attach for non-EPS services or "SMS only" (if requested by the UE in the ATTACH REQUEST) has failed

When the default bearer is activated as part of the attach procedure, the MME shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message together with ATTACH ACCEPT message. The IE ESM Message Container is used for this purpose. The network may also initiate the activation of dedicated bearers towards the UE by invoking the dedicated EPS bearer context activation procedure

The GUTI Reallocation may be part of the attach procedure. If the ATTACH REQUEST message includes the IMSI or IMEI, or if the MME considers the GUTI provided by the UE is invalid, or if the GUTI provided by the UE was assigned by another MME, the MME shall allocate a new GUTI to the UE. The MME shall include in the ATTACH ACCEPT message the new assigned GUTI together with the assigned TAI list

The IE TAI List indicates a list of tracking areas for which the UE doesn't need to perform a tracking area updating procedure when entered one of these TAs (in the list). The TAIs in a TAI list assigned by an MME to a UE belongs to the same MME area

The MME includes EMM Cause IE when IMSI attach for non-EPS services is not successful during a combined EPS/IMSI attach procedure

The purpose of the EPS network feature support IE is to indicate whether certain features are supported by the network. It can indicate the following features whether supported or not: IMS voice over PS session indicator (IMS VoPS), Emergency bearer services indicator (EMC BS), Location services indicator in EPC (EPC-LCS), Location services indicator in CS (CS-LCS), Support of EXTENDED SERVICE REQUEST for packet services (ESRPS)

The purpose of the Additional update result IE is to provide additional information about the result of a combined attach procedure. 00-no additional information; 01-CS Fallback not preferred; 10-SMS only; 11-reserved 

Reference: 3GPP TS 24.301

Example: ATTACH ACCEPT Message