| Protocol | nas | Network | lte |
|---|---|---|---|
| Spec | 3GPP TS 24.301 | Spec Section | 6.4.3, 8.3.18 |
| Direction | MME to UE | Message Type | ESM signaling |
| Full message name | LTE Modify 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 / Sent after a bearer already exists and the EPC wants the UE to apply a changed bearer definition. |
| Typical trigger | Triggered when policy, QoS, TFT, APN-AMBR, or another live bearer parameter changes. |
| Main purpose | Updates EPS QoS, TFT, APN-AMBR, or related bearer settings so the UE can apply a new bearer configuration without tearing the bearer down first. |
| Main specification | 3GPP TS 24.301, 6.4.3, 8.3.18 |
| Release added | Release 8 |
| Procedures where used | Modify EPS Bearer Context Procedure, Dedicated Bearer Policy Update |
Modify EPS Bearer Context Request is the LTE NAS message the network sends when it wants to change bearer parameters that are already active on the UE.
Updates EPS QoS, TFT, APN-AMBR, or related bearer settings so the UE can apply a new bearer configuration without tearing the bearer down first.
Modify EPS Bearer Context Request is the network telling the UE to change settings on a bearer that already exists.
Call flow position: Network bearer-modification message used when the EPC changes the live QoS or AMBR parameters of an active bearer.
Typical state: The bearer already exists, and the network is updating its active definition.
Preconditions:
Next likely message: Modify EPS Bearer Context Accept
Call flow position: Network bearer-modification message used when the traffic matching rules or related filter context change.
Typical state: The bearer stays active, but the packet-handling rules or associated parameters are changing.
Preconditions:
Next likely message: Modify EPS Bearer Context Accept
Previous message(s): Activate Default EPS Bearer Context Accept, Activate Dedicated EPS Bearer Context Accept, Bearer Resource Allocation Request
Next message(s): Modify EPS Bearer Context Accept
Security context: Protected by the active NAS security context because it changes live session-management state.
Modify EPS Bearer Context Request
New EPS QoS OPTIONAL
TFT OPTIONAL
New QoS OPTIONAL
Radio priority OPTIONAL
Packet flow identifier OPTIONAL
APN-AMBR OPTIONAL
Protocol configuration options OPTIONAL
WLAN offload indication OPTIONAL
NBIFOM container OPTIONAL
Header compression configuration OPTIONAL
Extended protocol configuration options OPTIONAL
Read this message from the changed bearer fields first. The key question is what live bearer parameter the network wanted to update.
Modify EPS Bearer Context Request
Protocol discriminator: EPS session management
EPS bearer identity: 6
Procedure transaction identity: 5
Message type: Modify EPS Bearer Context Request
New EPS QoS: QCI 1
TFT: add uplink packet filter for IMS signaling
APN-AMBR: DL 200000 kbps UL 100000 kbps
| IE | Required | Description |
|---|---|---|
New EPS QoS | Optional | Carries the updated EPS QoS settings for the bearer. |
TFT | Optional | Carries the updated traffic flow template or filter rules for the bearer. |
APN-AMBR | Optional | May update aggregate maximum bit rate settings tied to the PDN connection. |
Protocol configuration options | Optional | May carry related configuration data that belongs with the bearer update. |
New EPS QoSCarries the updated EPS QoS settings for the bearer.
Presence: Optional
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.
TFTCarries the updated traffic flow template or filter rules for the bearer.
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.
APN-AMBRMay update aggregate maximum bit rate settings tied to the PDN connection.
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 optionsMay carry related configuration data that belongs with the bearer update.
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.
Likely cause: The bearer may have been modified in place by Modify EPS Bearer Context Request.
What to inspect: Check the changed QoS, TFT, APN-AMBR, and later UE acceptance.
Next step: Treat the issue as a live bearer reconfiguration rather than a fresh bearer setup.
Activation creates a bearer. Modify EPS Bearer Context Request changes parameters on a bearer that already exists.
It is the EPS NAS message the network sends when it wants to change settings on a bearer that is already active.
Start with the field that changed, especially New EPS QoS, TFT, or APN-AMBR.
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.