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NASLTEUE to MME3GPP TS 24.301
LTE Control Plane Service Request
Control Plane Service Request is the LTE NAS message the UE sends when service restoration uses control-plane CIoT EPS optimization instead of the normal user-plane service request path.
Message Fact Sheet
Protocol
nas
Network
lte
Spec
3GPP TS 24.301
Spec Section
5.6.1, Release 18 control plane service request procedure
Direction
UE to MME
Message Type
EMM signaling
Full message name
LTE Control Plane Service Request
Protocol
NAS
Technology
LTE
Direction
UE to MME
Interface
N1 over LTE access / S1-MME control path
Signaling bearer / channel
NAS signaling / Commonly carried after RRC resume or paging when the UE uses control-plane CIoT EPS optimization.
Typical trigger
Triggered when the UE uses control-plane CIoT EPS optimization for mobile-originated data, mobile-terminated paging response, or control-plane SMS or NAS signaling.
Main purpose
Requests mobile-originated or mobile-terminated service continuation over the control plane, optionally carrying NAS or ESM payload that avoids setting up user-plane bearers first.
Main specification
3GPP TS 24.301, 5.6.1, Release 18 control plane service request procedure
Release added
Release 13
Procedures where used
LTE Service Request Procedure, Control Plane CIoT EPS Optimization, SMS over NAS
What is LTE Control Plane Service Request in simple terms?
Control Plane Service Request is the LTE NAS message the UE sends when service restoration uses control-plane CIoT EPS optimization instead of the normal user-plane service request path.
Requests mobile-originated or mobile-terminated service continuation over the control plane, optionally carrying NAS or ESM payload that avoids setting up user-plane bearers first.
Why this message matters
Control Plane Service Request is the LTE NAS message the UE uses when service restoration stays on the control plane instead of the normal user-plane branch.
Where this message appears in the call flow
Mobile-originated control-plane user data
When the UE has small user data to send through the control plane, Control Plane Service Request opens the CIoT-oriented restore branch.
Call flow position: UE-originated service restore message used when the UE sends small user data through the control plane.
Typical state: The UE already has EPS registration and is restoring service without first opening the normal user-plane bearer path.
Preconditions:
The UE supports control-plane CIoT EPS optimization.
Pending small data or signaling should use the control plane.
Next likely message: Service Accept or common NAS continuation
Paging-triggered control-plane service
After paging, the UE can continue the mobile-terminated control-plane service branch with Control Plane Service Request.
Call flow position: UE response message after paging when the mobile-terminated branch continues through control-plane CIoT service restoration.
Typical state: The UE woke up from paging and is continuing the service branch through control-plane service signaling.
Preconditions:
Paging triggered the service restore.
The branch uses control-plane CIoT handling.
Next likely message: Service Accept, Downlink NAS Transport, or common NAS continuation
Control-plane SMS or NAS signaling
For SMS over NAS or another small control-plane service branch, the UE may carry the payload through Control Plane Service Request.
Call flow position: UE-originated service restore message used for SMS over NAS or similar control-plane signaling.
Typical state: The UE needs signaling continuity but does not need a full user-plane setup first.
Preconditions:
The service case allows control-plane transport.
Next likely message: Service Accept, Downlink NAS Transport, or reject handling
Interface: N1 over LTE access / S1-MME control path
Domain: Core-side EPS mobility management signaling for service restoration with control-plane user-data handling.
Signaling bearer: NAS signaling
Logical channel: Commonly carried after RRC resume or paging when the UE uses control-plane CIoT EPS optimization.
Transport / encapsulation: EPS NAS message sent by the UE toward the MME through the eNodeB during CIoT-oriented service restoration.
Security context: Normally protected by an existing NAS security context because the UE is already EPS-registered and is restoring service.
Message Structure Overview
Control Plane Service Request is an EPS mobility-management message rather than an ASN.1 LTE RRC structure.
The practical reading path starts with Control plane service type, then checks whether an ESM or NAS message container is present.
In real traces, this message explains why the UE restored service through the control plane instead of the normal Service Request or Extended Service Request branch.
ASN.1 Message Syntax for LTE Control Plane Service Request
Control Plane Service Request
Control plane service type
KSI and sequence information
ESM message container OPTIONAL
NAS message container OPTIONAL
EPS bearer context status OPTIONAL
Device properties OPTIONAL
UE request type OPTIONAL
Paging restriction OPTIONAL
How to read this message syntax
Control Plane Service Request is a NAS message, not an ASN.1 LTE RRC message. Read it first from Control plane service type and from whether the branch carries ESM or NAS payload.
LTE Control Plane Service Request - Example Dump
Control Plane Service Request
Protocol discriminator: EPS mobility management
Security header type: Integrity protected and ciphered
Message type: Control Plane Service Request
Control plane service type: mobile originating request, active flag set
ESM message container: ESM Data Transport
UE request type: NAS signaling connection release
How to read this dump
Start with Control plane service type because it tells you whether the branch is mobile-originated or mobile-terminated.
Then check whether the message carries an ESM or NAS message container.
If both containers are absent, read the trace as a control-plane restore signal rather than a data-carrying branch.
Important Information Elements
IE
Required
Description
Control plane service type
Yes
Tells the network whether the branch is mobile-originated or mobile-terminated and whether the request is active.
ESM message container
Optional
May carry ESM Data Transport when the UE needs to move small data through the control plane.
NAS message container
Optional
May carry SMS or another NAS payload that belongs to the control-plane service branch.
UE request type
Optional
Can refine the branch, for example when the UE requests NAS signaling connection release.
Paging restriction
Optional
May indicate paging-related handling preferences in control-plane CIoT branches.
Detailed field explanation
Control plane service type
Tells the network whether the branch is mobile-originated or mobile-terminated and whether the request is active.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
ESM message container
May carry ESM Data Transport when the UE needs to move small data through the control plane.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
NAS message container
May carry SMS or another NAS payload that belongs to the control-plane service branch.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
UE request type
Can refine the branch, for example when the UE requests NAS signaling connection release.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
Paging restriction
May indicate paging-related handling preferences in control-plane CIoT branches.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
What to check in logs and traces
Confirm the branch is using control-plane CIoT EPS optimization.
Check Control plane service type first.
Inspect whether ESM Data Transport or a NAS message container is present.
Correlate the message with later Service Accept, Service Reject, or Downlink NAS Transport.
Common Issues and Troubleshooting
The UE restores service, but no user-plane bearer appears.
Likely cause: The branch may be intentionally using control-plane CIoT transport instead of the normal user-plane service request path.
What to inspect: Check Control plane service type and whether an ESM or NAS message container is present.
Next step: Treat the trace as a control-plane service branch before blaming bearer setup.
Paging resumes the UE, but the service continuation looks different from normal Service Request handling.
Likely cause: The network and UE may be using the control-plane CIoT service path.
What to inspect: Read Paging, Control Plane Service Request, and any later Downlink NAS Transport together.
Next step: Decide first whether the mobile-terminated service is supposed to stay on the control plane.
LTE / 5G / Variant Comparison
Compared with Service Request
Service Request restores service through the normal LTE NAS branch. Control Plane Service Request is the control-plane CIoT variant.
Compared with Extended Service Request
Extended Service Request carries fallback and packet-services-via-S1 branch context. Control Plane Service Request carries CIoT-oriented control-plane service context.
FAQ
What is Control Plane Service Request in LTE?
It is the EPS NAS message the UE sends when service restoration uses control-plane CIoT EPS optimization instead of the normal user-plane branch.
What should I inspect first?
Start with Control plane service type and whether the message carries an ESM or NAS message container.
Why is it important in troubleshooting?
Because it explains why the trace may continue without the usual bearer setup and instead carry data or signaling directly on the control plane.
Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.
