NAS ESM – Non Access Stratum EPS Session Management
In LTE, the NAS protocol is used between the User Equipment and the MME in order to facilitate EPS Mobility Management and EPS Session Management procedures. Consequently, NAS protocol messages are classified as EMM or ESM, both of which can potentially be found in a single NAS message. An example of this would be during the Initial Attach, where the first message sent by the mobile includes an EMM Attach Request, in addition to an ESM PDN Connectivity Request. Generally, NAS ESM messages are associated with user data sessions, such as establishing, modifying or terminated EPS bearers.
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