Cause values for EPS mobility management

The main function of the mobility management sublayer is to support the mobility of a user equipment, such as informing the network of its present location and providing user identity confidentiality.

A further function of the mobility management sublayer is to provide connection management services to the session management (SM) sublayer and the short message services (SMS) entity of the connection management (CM) sublayer.

MME/S4-SGSN mapping table between S11/S4 and NAS Cause values

The MME/S4-SGSN initiates session management requests towards the SGW and PGW or mobility management requests towards the source/target MME/S4-SGSN. If this operation is not successful, there are several possible cause codes, which need to be mapped to the appropriate cause codes over NAS to the UE.

Additionally, the MME/S4-SGSN initiates session management requests towards the UE. If this operation is not successful, there are several possible NAS cause codes which need to be mapped to the appropriate GTP cause codes over S11/S4 interface towards the SGW.

The MME/S4-SGSN should map these cause codes as defined in tables C.1 to C.5 unless specified otherwise in the tables.

GTPv2 Cause Codes

The cause code value in the GTPv2 message can indicate what happened between MME, SGW, and PGW so as to simplify the troubleshooting process.

The cause value must be included in the GTPv2 message response. In the message response, the Cause value indicates the acceptance or rejection of the corresponding message request. Cause value indicates an explicit reason for the refusal.

Cause values ​​can also be included in message requests. In the request message, the Cause value indicates the reason for the request.