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NASLTEMME to UE3GPP TS 24.301
LTE Activate Default EPS Bearer Context Request
Activate Default EPS Bearer Context Request is the EPS session-management message the network sends to the UE when it wants to activate the default bearer for a PDN connection.
Message Fact Sheet
Protocol
nas
Network
lte
Spec
3GPP TS 24.301
Spec Section
6.4.1.2, 8.3.6
Direction
MME to UE
Message Type
ESM signaling
Full message name
LTE Activate Default EPS Bearer Context Request
Protocol
NAS
Technology
LTE
Direction
MME to UE
Interface
N1 over LTE access / S1-MME control path
Signaling bearer / channel
NAS signaling / Commonly carried inside the ESM message container of Attach Accept during initial attach, or later in downlink NAS transport for standalone PDN-connectivity handling.
Typical trigger
Sent when the network accepts PDN connectivity and is ready to activate the default EPS bearer for that PDN connection.
Main purpose
Carries the bearer parameters, APN context, EPS QoS, and related configuration the UE needs to create the default EPS bearer for the accepted PDN connection.
What is LTE Activate Default EPS Bearer Context Request in simple terms?
Activate Default EPS Bearer Context Request is the EPS session-management message the network sends to the UE when it wants to activate the default bearer for a PDN connection.
Carries the bearer parameters, APN context, EPS QoS, and related configuration the UE needs to create the default EPS bearer for the accepted PDN connection.
Why this message matters
Activate Default EPS Bearer Context Request is the network telling the UE exactly how to activate the default bearer for the PDN connection.
Where this message appears in the call flow
Initial attach default bearer activation
In the initial attach path, Activate Default EPS Bearer Context Request is commonly embedded in Attach Accept and drives the default bearer setup the UE confirms during attach completion.
Call flow position: Embedded ESM activation message delivered together with Attach Accept when the network grants the first PDN connection during attach.
Typical state: The attach path has been accepted and the network is now telling the UE how to activate the default bearer that makes the new PDN connection usable.
Preconditions:
The attach procedure was accepted.
The network decided to establish the default bearer for the accepted PDN connection.
Next likely message: Attach Complete with bearer acceptance continuation
Standalone PDN connectivity bearer activation
After a standalone PDN Connectivity Request is accepted, the network sends Activate Default EPS Bearer Context Request to define the default bearer for that PDN connection.
Call flow position: Network bearer-activation message sent after a standalone PDN Connectivity Request outside the initial attach branch.
Typical state: The UE is already registered and the network is now returning the accepted default bearer parameters for the requested PDN.
Preconditions:
The UE sent a standalone PDN Connectivity Request.
The network accepted that PDN request and prepared default bearer parameters.
Next likely message: Activate Default EPS Bearer Context Accept or Reject
Additional APN or IMS default bearer activation
For IMS or another APN, Activate Default EPS Bearer Context Request shows the network-side bearer definition returned after the additional PDN request is accepted.
Call flow position: Network activation message used when another PDN connection such as IMS is accepted after the UE already has an earlier EPS context.
Typical state: The UE is not creating the first overall EPS context, but it is creating another default bearer for a different PDN connection.
Preconditions:
The UE requested another PDN connection.
The network accepted the additional APN or IMS PDN request.
Next likely message: Activate Default EPS Bearer Context Accept or Reject
Interface: N1 over LTE access / S1-MME control path
Domain: Core-side EPS session management signaling for bearer establishment after PDN connectivity has been accepted.
Signaling bearer: NAS signaling
Logical channel: Commonly carried inside the ESM message container of Attach Accept during initial attach, or later in downlink NAS transport for standalone PDN-connectivity handling.
Transport / encapsulation: EPS NAS ESM message sent by the MME and delivered to the UE through the eNodeB as part of default bearer activation.
Security context: Activate Default EPS Bearer Context Request is normally received after the wider NAS path is already trusted enough for bearer activation, so it is commonly seen in protected continuation rather than raw early access.
Message Structure Overview
Activate Default EPS Bearer Context Request is an EPS session-management message rather than an ASN.1 LTE RRC structure.
The practical reading path starts with EPS QoS, APN, PDN address, and whether the message is embedded in Attach Accept or sent as standalone bearer activation.
In real traces, this message explains exactly what default bearer the network is trying to activate for the UE.
Activate Default EPS Bearer Context Request
EPS QoS
Access point name
PDN address
Transaction identifier OPTIONAL
Negotiated QoS OPTIONAL
Packet flow identifier OPTIONAL
APN-AMBR OPTIONAL
Protocol configuration options OPTIONAL
Negotiated LLC SAPI OPTIONAL
ESM cause OPTIONAL
Radio priority OPTIONAL
Connectivity type OPTIONAL
WLAN offload indication OPTIONAL
Header compression configuration OPTIONAL
Control plane only indication OPTIONAL
Extended protocol configuration options OPTIONAL
How to read this message syntax
Activate Default EPS Bearer Context Request is a NAS layer-3 ESM message, not an ASN.1 LTE RRC message. Read it from the bearer-definition fields first because this message tells the UE what default bearer to build.
LTE Activate Default EPS Bearer Context Request - Example Dump
Start by deciding whether the message is embedded in Attach Accept or follows a standalone PDN Connectivity Request.
EPS QoS, APN, and PDN address are the highest-value fields because they define the bearer the UE is expected to activate.
If the bearer setup later fails, this message is the best place to confirm what the network actually offered.
Important Information Elements
IE
Required
Description
EPS QoS
Yes
Defines the bearer QoS parameters returned by the network for the default bearer.
Access point name
Yes
Identifies the APN associated with the PDN connection being activated.
PDN address
Yes
Provides the IP address or related PDN addressing information assigned to the UE for the connection.
Transaction identifier
Optional
Helps relate the activation message to the UE-requested PDN-connectivity procedure.
Protocol configuration options
Optional
Carries additional configuration such as DNS or APN-related options returned by the network.
Detailed field explanation
EPS QoS
Defines the bearer QoS parameters returned by the network for the default bearer.
Presence: Required
In practice: QoS rules are the real service profile of the session. Inspect the QFI mapping, packet filters, and precedence because those values explain how user traffic will actually be classified and forwarded.
Access point name
Identifies the APN associated with the PDN connection being activated.
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.
PDN address
Provides the IP address or related PDN addressing information assigned to the UE for the connection.
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.
Transaction identifier
Helps relate the activation message to the UE-requested PDN-connectivity procedure.
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.
Protocol configuration options
Carries additional configuration such as DNS or APN-related options returned by the network.
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 whether the activation is part of attach or part of standalone PDN-connectivity handling.
Inspect Protocol configuration options when DNS or other returned configuration matters.
Correlate the message with the earlier PDN Connectivity Request and the later accept or reject response.
If attach is involved, read the message together with Attach Accept and Attach Complete.
Common Issues and Troubleshooting
Attach succeeds, but usable packet service still does not come up.
Likely cause: The attach branch may be healthy, but the embedded default bearer activation may fail or contain unexpected APN, QoS, or address information.
What to inspect: Check Attach Accept, the embedded Activate Default EPS Bearer Context Request, and the later accept or reject behavior.
Next step: Read attach grant and bearer activation as one combined path instead of treating them as separate problems.
A standalone PDN request is accepted, but the UE still does not get working PDN service.
Likely cause: The network may have returned bearer parameters the UE cannot apply cleanly, or the bearer-activation branch may fail afterward.
What to inspect: Check the earlier PDN Connectivity Request, the returned APN and PDN address, and the UE accept or reject response.
Next step: Decide first whether the issue is bearer definition, APN policy, or a later user-plane problem.
The network repeats bearer activation requests.
Likely cause: The activation branch may still be under T3485 supervision because the UE did not complete the bearer-activation response cleanly.
What to inspect: Check for repeated Activate Default EPS Bearer Context Request messages and whether the UE sent accept, reject, or nothing.
Next step: Treat the trace as a bearer-activation supervision issue before blaming earlier attach or PDN-connectivity signaling.
LTE / 5G / Variant Comparison
Compared with PDN Connectivity Request
PDN Connectivity Request is the UE asking for PDN connectivity. Activate Default EPS Bearer Context Request is the network response that defines the default bearer for the accepted PDN.
Compared with Attach Accept
Attach Accept grants EPS mobility context. Activate Default EPS Bearer Context Request defines the bearer and PDN-side service context that often ride inside that attach response.
Compared with Activate Default EPS Bearer Context Accept
Activate Default EPS Bearer Context Request is the network instruction. Activate Default EPS Bearer Context Accept is the UE confirming that it activated the default bearer.
FAQ
What is Activate Default EPS Bearer Context Request in LTE?
It is the EPS NAS session-management message the network sends to the UE to activate the default bearer for a PDN connection.
Is this message only used during attach?
No. It often appears inside Attach Accept during initial attach, but it can also be sent after a standalone PDN Connectivity Request.
What should I inspect first in this message?
Start with EPS bearer identity, EPS QoS, APN, PDN address, and whether the message belongs to attach or standalone PDN-connectivity handling.
Why is this message important in troubleshooting?
Because it shows exactly what bearer and PDN parameters the network asked the UE to activate.
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.
