LTE NAS Messages – Complete EPS Mobility and Session Management Message List

LTE NAS, or Non-Access Stratum signalling, is the control-plane signalling between the UE and the EPC/MME. Defined mainly in 3GPP TS 24.301, LTE NAS includes EPS Mobility Management (EMM) and EPS Session Management (ESM) messages used for attach, authentication, security, tracking area update, service request, detach, PDN connectivity, bearer setup, bearer modification, and bearer release.

Use this page to search or browse LTE NAS messages by procedure category. Each message page explains the message direction, trigger, call-flow role, key fields, and practical troubleshooting notes.

Based on 3GPP TS 24.301

Search LTE NAS messages

60 LTE NAS messages shown

Attach Messages

EMM messages used when the UE attaches to the LTE/EPC network and receives EPS registration and bearer context.

UE to MME Attach Request

Starts EPS registration and initial access to LTE/EPC service.

MME to UE Attach Accept

Accepts EPS registration and delivers attach result context.

UE to MME Attach Complete

Confirms that the UE accepted the attach result.

MME to UE Attach Reject

Rejects EPS attach with a cause and retry behavior.

Authentication Messages

EMM messages used for EPS AKA authentication and authentication failure handling.

MME to UE Authentication Request

Challenges the UE with EPS AKA authentication data.

UE to MME Authentication Response

Returns the UE authentication response to the MME.

MME to UE Authentication Reject

Rejects authentication and prevents continuation.

UE to MME Authentication Failure

Reports UE-side authentication failure or sync problems.

Security Messages

EMM messages used to activate NAS security algorithms and reject unsupported or invalid security mode control.

MME to UE Security Mode Command

Selects and activates NAS security algorithms.

UE to MME Security Mode Complete

Confirms NAS security mode activation.

UE to MME Security Mode Reject

Rejects NAS security mode control.

Tracking Area Update Messages

EMM messages used when the UE updates tracking area, mobility state, or registration information.

UE to MME Tracking Area Update Request

Starts a TAU mobility or registration update.

MME to UE Tracking Area Update Accept

Accepts the TAU and returns updated mobility context.

UE to MME Tracking Area Update Complete

Confirms completion of the accepted TAU.

MME to UE Tracking Area Update Reject

Rejects the TAU with mobility handling cause.

Service Request Messages

EMM messages used when the UE requests user-plane or signalling service while already registered.

UE to MME Service Request

Requests service restoration for a registered UE.

MME to UE Service Reject

Rejects the service request with cause handling.

UE to MME Extended Service Request

Requests extended service such as CS fallback related handling.

UE to MME Control Plane Service Request

Requests control-plane service for CIoT-style handling.

Detach Messages

EMM messages used when the UE or network detaches from EPS service.

UE to MME or MME to UE Detach Request

Starts UE-initiated or network-initiated EPS detach.

MME to UE or UE to MME Detach Accept

Confirms that detach has completed.

Identity Messages

EMM messages used to request and provide UE identity information such as IMSI, GUTI, or IMEI.

MME to UE Identity Request

Asks the UE for an identity value.

UE to MME Identity Response

Returns the requested UE identity.

EMM Status and Information

Messages used for EMM error reporting and network information delivery.

UE to MME EMM Status

Reports an EPS mobility-management protocol error.

MME to UE EMM Information

Delivers network name, time, or information display data.

PDN Connectivity Messages

ESM messages used when the UE requests, accepts, or rejects PDN connectivity and default EPS bearer establishment.

UE to MME PDN Connectivity Request

Requests a PDN connection and default bearer.

Coming soon PDN Connectivity Reject

Rejects a PDN connectivity attempt.

UE to MME PDN Disconnect Request

Requests release of a PDN connection.

MME to UE PDN Disconnect Reject

Rejects a PDN disconnect request.

EPS Bearer Activation Messages

ESM messages used to activate default or dedicated EPS bearers.

MME to UE Activate Default EPS Bearer Context Request

Creates the default EPS bearer context.

UE to MME Activate Default EPS Bearer Context Accept

Accepts default bearer activation.

UE to MME Activate Default EPS Bearer Context Reject

Rejects default bearer activation.

MME to UE Activate Dedicated EPS Bearer Context Request

Creates a dedicated EPS bearer context.

UE to MME Activate Dedicated EPS Bearer Context Accept

Accepts dedicated bearer activation.

UE to MME Activate Dedicated EPS Bearer Context Reject

Rejects dedicated bearer activation.

EPS Bearer Modification Messages

ESM messages used to modify EPS bearer context, QoS, TFT, or bearer-level parameters.

MME to UE Modify EPS Bearer Context Request

Requests a bearer context update.

UE to MME Modify EPS Bearer Context Accept

Accepts bearer context modification.

UE to MME Modify EPS Bearer Context Reject

Rejects bearer context modification.

UE to MME Bearer Resource Allocation Request

Requests network allocation of bearer resources.

MME to UE Bearer Resource Allocation Reject

Rejects bearer resource allocation.

UE to MME Bearer Resource Modification Request

Requests modification of bearer resources.

MME to UE Bearer Resource Modification Reject

Rejects bearer resource modification.

EPS Bearer Deactivation Messages

ESM messages used to deactivate EPS bearer contexts and confirm bearer release.

MME to UE Deactivate EPS Bearer Context Request

Requests EPS bearer context release.

UE to MME Deactivate EPS Bearer Context Accept

Confirms bearer context release.

ESM Status and Information

Messages used for ESM error reporting and session-management status handling.

MME to UE ESM Information Request

Requests missing ESM information such as APN details.

UE to MME ESM Information Response

Returns requested ESM information.

UE to MME ESM Status

Reports an EPS session-management protocol error.

Other / Advanced

Additional LTE NAS messages used for later releases, CIoT, emergency, SMS over NAS, or operator-specific behaviours if present in the project.

MME to UE CS Service Notification

CS Service Notification is the LTE NAS message the network sends when it needs to notify the UE about an incoming CS-related service branch such as CS fallback.

MME to UE Downlink Generic NAS Transport

Downlink Generic NAS Transport is the LTE NAS message the network sends when it needs to carry a generic payload through the EMM layer.

MME to UE Downlink NAS Transport

Downlink NAS Transport is the EPS mobility-management message the network sends to carry an encapsulated SMS NAS payload toward the UE over LTE NAS signaling.

UE to MME ESM Data Transport

ESM Data Transport is the LTE NAS message used to carry small user data through the control plane when control-plane CIoT EPS optimization is in use.

UE to MME ESM Dummy Message

ESM Dummy Message is the LTE NAS session-management message used as a minimal protected ESM payload in specific control-plane or procedure-maintenance branches.

MME to UE GUTI Reallocation Command

GUTI Reallocation Command is the LTE NAS message the MME sends when it wants the UE to replace its current GUTI with a newly allocated identity.

UE to MME GUTI Reallocation Complete

GUTI Reallocation Complete is the LTE NAS message the UE sends to confirm that it accepted and stored the new GUTI.

MME to UE Notification

Notification is the LTE NAS message the network sends when it needs to inform the UE about a specific NAS-side event that affects later handling.

UE to MME Remote UE Report

Remote UE Report is the LTE NAS message used in remote UE or CIoT handling to report remote-device status or event information toward the network.

MME to UE Remote UE Report Response

Remote UE Report Response is the LTE NAS message the network sends after it processes a Remote UE Report.

MME to UE Service Accept

Service Accept is the EPS NAS message the network sends when the service request procedure is accepted and active service can continue using the existing EPS context.

UE to MME Uplink Generic NAS Transport

Uplink Generic NAS Transport is the LTE NAS message the UE sends when it needs to carry a generic payload through the EMM transport branch.

UE to MME Uplink NAS Transport

Uplink NAS Transport is the EPS mobility-management message the UE sends to carry an encapsulated SMS NAS payload toward the network over LTE NAS signaling.

Most Used LTE NAS Messages

Attach Request Starts EPS registration and initial access to LTE/EPC service. Attach Accept Accepts EPS registration and delivers attach result context. Authentication Request Challenges the UE with EPS AKA authentication data. Authentication Response Returns the UE authentication response to the MME. Security Mode Command Selects and activates NAS security algorithms. Security Mode Complete Confirms NAS security mode activation. Tracking Area Update Request Starts a TAU mobility or registration update. Service Request Requests service restoration for a registered UE. Detach Request Starts UE-initiated or network-initiated EPS detach. PDN Connectivity Request Requests a PDN connection and default bearer. Activate Default EPS Bearer Context Request Creates the default EPS bearer context. Activate Dedicated EPS Bearer Context Request Creates a dedicated EPS bearer context. EMM Status Reports an EPS mobility-management protocol error. ESM Status Reports an EPS session-management protocol error.

Common LTE NAS Procedure Flows

LTE Attach

Attach Request -> Authentication Request/Response -> Security Mode Command/Complete -> Attach Accept -> Attach Complete

Tracking Area Update

Tracking Area Update Request -> Tracking Area Update Accept / Reject -> Tracking Area Update Complete

Service Request

Service Request -> network resumes signalling/user-plane resources or returns Service Reject

Detach

Detach Request -> Detach Accept

PDN Connectivity

PDN Connectivity Request -> Activate Default EPS Bearer Context Request -> Attach Accept / ESM accept handling

Dedicated Bearer Activation

Activate Dedicated EPS Bearer Context Request -> Activate Dedicated EPS Bearer Context Accept / Reject

Bearer Modification

Modify EPS Bearer Context Request -> Modify EPS Bearer Context Accept / Reject

Bearer Release

Deactivate EPS Bearer Context Request -> Deactivate EPS Bearer Context Accept

FAQ

What are LTE NAS messages?

LTE NAS messages are Non-Access Stratum signalling messages exchanged between the UE and EPC/MME to support attach, authentication, security, tracking area update, service request, detach, and EPS bearer/session management.

Which specification defines LTE NAS?

LTE NAS is mainly defined in 3GPP TS 24.301.

What is the difference between EMM and ESM?

EMM handles EPS mobility management such as attach, authentication, security, tracking area update, service request, and detach. ESM handles EPS session management such as PDN connectivity and EPS bearer activation, modification, and deactivation.

What are the most important LTE NAS messages?

Commonly analyzed LTE NAS messages include Attach Request, Attach Accept, Authentication Request, Authentication Response, Security Mode Command, Security Mode Complete, Tracking Area Update Request, Service Request, PDN Connectivity Request, and Activate Default EPS Bearer Context Request.

What is Attach Request used for?

Attach Request starts EPS registration and allows the UE to request access to LTE/EPC services.

What is PDN Connectivity Request used for?

PDN Connectivity Request is an ESM message used by the UE to request connection to a PDN and establish a default EPS bearer.

What is the difference between LTE NAS and LTE RRC?

LTE RRC runs between UE and eNodeB for radio connection control, while LTE NAS runs between UE and EPC/MME for mobility and session management.

References

3GPP TS 24.301 - Non-Access-Stratum protocol for EPS
3GPP TS 23.401 - GPRS enhancements for E-UTRAN access
3GPP TS 36.331 - LTE RRC protocol specification
3GPP TS 36.413 - S1AP protocol specification