Elementary procedures for EPS mobility management

Elementary procedures 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.

Types of EMM procedures

Depending on how they can be initiated, three types of EMM procedures can be distinguished:

1)   EMM common procedures:

      An EMM common procedure can always be initiated whilst a NAS signalling connection exists.               The procedures belonging to this type are:

      Initiated by the network:

-     GUTI reallocation;

-     authentication;

-     security mode control;

-     identification;

-     EMM information.

2)   EMM specific procedures:

      At any time only one UE initiated EMM specific procedure can be running. The procedures 

      belonging to this type are:

      Initiated by the UE and used to attach the IMSI in the network for EPS services and/or non-EPS              services, and to establish an EMM context and a default bearer:

-     attach and combined attach.

      Initiated by the UE and used to attach the IMSI or IMEI for emergency bearer services, and to                 establish an EMM context and a default bearer to a PDN that provides emergency bearer services:

-     attach.

      Initiated by the UE or the network and used to detach the IMSI in the network for EPS services               and/or non-EPS services and to release an EMM context and all bearers:

-     detach andcombined detach.

      Initiated by the UE when an EMM context has been established:

-     normal tracking area updating and combined tracking area updating (S1 mode only);

-     periodic tracking area updating (S1 mode only).

      The tracking area updating procedure can be used to request also the resource reservation for                sending data.

3)   EMM connection management procedures (S1 mode only):

      Initiated by the UE and used to establish a secure connection to the network or to request the               resource reservation for sending data, or both:

-     service request.

      The service request procedure can only be initiated if no UE initiated EMM specific procedure is          ongoing.

      Initiated by the network and used to request the establishment of a NAS signalling connection or         to prompt the UE to re-attach if necessary as a result of a network failure:

-     paging procedure.

      Initiated by the UE or the network and used to transport NAS messages:

-     transport of NAS messages.

      The transport of NAS messages procedure cannot be initiated while an EMM specific procedure         or a service request procedure is ongoing.