| Protocol | e1ap | Network | 5g |
|---|---|---|---|
| Spec | 3GPP TS 37.483 | Spec Section | Bearer Context Setup procedure and related IE definitions (Release 18 baseline) |
| Direction | gNB-CU-CP -> gNB-CU-UP initiatingMessage | Message Type | UE-associated bearer-context establishment control |
| Full message name | 5G E1AP - Bearer Context Setup Request |
|---|---|
| Protocol | E1AP |
| Technology | 5G |
| Direction | gNB-CU-CP -> gNB-CU-UP initiatingMessage |
| Interface | E1 between gNB-CU-CP and gNB-CU-UP |
| Signaling bearer / channel | UE-associated E1AP signaling / SCTP carried E1AP initiatingMessage |
| Typical trigger | The CU-CP has accepted or is continuing a UE procedure that requires CU-UP bearer creation, such as initial user-plane establishment, PDU session resource activation, or later DRB addition for an existing UE. |
| Main purpose | Creates the CU-UP side bearer context for a UE so the user plane can be anchored, QoS can be enforced, and NG-U and F1-U related user-plane behavior can continue under CU-CP control. |
| Main specification | 3GPP TS 37.483, Bearer Context Setup procedure and related IE definitions (Release 18 baseline) |
| Release added | Release 17 |
| Procedures where used | Initial user-plane bearer establishment, PDU session resource activation, DRB addition for an established UE |
Bearer Context Setup Request is the E1AP message the gNB-CU-CP sends to the gNB-CU-UP to create the user-plane bearer context, including PDU session, DRB, QoS, and NG-U transport instructions for one UE.
Creates the CU-UP side bearer context for a UE so the user plane can be anchored, QoS can be enforced, and NG-U and F1-U related user-plane behavior can continue under CU-CP control.
Bearer Context Setup Request is the CU-CP telling the CU-UP to build the UE's user-plane bearer state.
Call flow position: The CU-CP has decided which PDU sessions and DRBs should be anchored at the CU-UP and sends the first E1AP bearer build command.
Typical state: Control-plane UE context exists, but the CU-UP still needs enough bearer and transport detail to create the corresponding user-plane state.
Preconditions:
Next likely message: Bearer Context Setup Response
Call flow position: The setup request carries the security and bearer details the CU-UP needs before user-plane handling can continue.
Typical state: The CU-UP is being instructed how to interpret the user-plane branch for the UE, including transport and DRB-related context.
Preconditions:
Next likely message: Bearer Context Setup Response or Bearer Context Setup Failure
Previous message(s): Initial Context Setup Request, PDU Session Resource Setup Request, RRC Reconfiguration
Next message(s): Bearer Context Setup Response, Bearer Context Setup Failure, Bearer Context Modification Request
Security context: Bearer Context Setup Request does not create NAS security. It carries the security and bearer-control information the CU-UP needs in order to build the user-plane context that corresponds to the UE's already selected access and session state.
BearerContextSetupRequest ::= SEQUENCE {
protocolIEs ProtocolIE-Container { {BearerContextSetupRequest-IEs} },
...
}
BearerContextSetupRequest-IEs E1AP-PROTOCOL-IES ::= {
{ gNB-CU-CP UE E1AP ID, mandatory } |
{ Security Information, optional } |
{ UE DL Aggregate Maximum Bit Rate, optional } |
{ System Bearer Context Setup Request, mandatory },
...
}
Read the message as the control-plane instruction set the CU-UP needs in order to create bearer state. The exact payload depth sits inside the system bearer context rather than in the top-level wrapper alone.
E1AP-PDU
initiatingMessage
procedureCode: id-bearerContextSetup
criticality: reject
value: BearerContextSetupRequest
protocolIEs:
- id: id-gNB-CU-CP-UE-E1AP-ID
value: 0x00004192
- id: id-SecurityInformation
value:
integrity-protection: enabled
confidentiality-protection: enabled
- id: id-UEDLAggregateMaximumBitRate
value: 400000000
- id: id-System-BearerContextSetupRequest
value:
pdu-session-list:
- pdu-session-id: 10
drb-to-setup-list:
- drb-id: 4
qos-flow-list:
- qfi: 9
| IE | Required | Description |
|---|---|---|
gNB-CU-CP UE E1AP ID | Yes | Mandatory CU-CP side UE identifier used to correlate the setup request with the wider UE context. |
Security Information | Optional | Optional but operationally important security-related context the CU-UP needs for correct user-plane handling. |
UE DL Aggregate Maximum Bit Rate | Optional | Optional aggregate downlink rate limit that influences CU-UP bearer enforcement for the UE. |
System Bearer Context Setup Request | Yes | Mandatory bearer payload containing the session, DRB, QoS, and user-plane transport information the CU-UP must instantiate. |
gNB-CU-CP UE E1AP IDMandatory CU-CP side UE identifier used to correlate the setup request with the wider UE context.
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.
Security InformationOptional but operationally important security-related context the CU-UP needs for correct user-plane handling.
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 DL Aggregate Maximum Bit RateOptional aggregate downlink rate limit that influences CU-UP bearer enforcement for the UE.
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.
System Bearer Context Setup RequestMandatory bearer payload containing the session, DRB, QoS, and user-plane transport information the CU-UP must instantiate.
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.
Likely cause: The setup request may be missing required bearer details or the CU-UP may reject the requested bearer payload.
What to inspect: Read the system bearer context payload and then compare it with the later setup response or failure.
Next step: Validate the requested session and DRB structure before debugging the data path itself.
Likely cause: The requested bearer model and the accepted CU-UP result may differ, or the setup request may not carry the intended QoS branch.
What to inspect: Correlate requested DRB and QoS items with the later response payload.
Next step: Drive the investigation from request-versus-response deltas rather than from the request alone.
Setup creates the CU-UP bearer context for the UE. Modification changes an already existing bearer context in place.
It is the E1AP message the gNB-CU-CP sends to the gNB-CU-UP to create the UE's bearer context on the user-plane side.
The gNB-CU-CP sends it to the gNB-CU-UP over the E1 interface.
It mainly carries the UE identifier plus the bearer-context setup payload that defines session, DRB, QoS, and transport-related user-plane state.
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.