What is CS Service Notification in LTE?
It is the LTE NAS message the network sends to notify the UE about a pending CS-related service branch.
| Protocol | nas | Network | lte |
|---|---|---|---|
| Spec | 3GPP TS 24.301 | Spec Section | Release 18 message definition for CS Service Notification |
| Direction | MME to UE | Message Type | EMM signaling |
| Full message name | LTE CS Service Notification |
|---|---|
| Protocol | NAS |
| Technology | LTE |
| Direction | MME to UE |
| Interface | N1 over LTE access / S1-MME control path |
| Signaling bearer / channel | NAS signaling / Sent while the UE is EPS-registered and the network needs to notify a CS-related incoming service condition. |
| Typical trigger | Triggered when the network needs to notify the UE about incoming CS fallback or related service handling. |
| Main purpose | Alerts the UE that a CS-oriented service path is pending so the UE can continue the correct extended or fallback service branch. |
| Main specification | 3GPP TS 24.301, Release 18 message definition for CS Service Notification |
| Release added | Release 8 |
| Procedures where used | CS Fallback, Service Notification Handling |
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.
Alerts the UE that a CS-oriented service path is pending so the UE can continue the correct extended or fallback service branch.
CS Service Notification tells the UE that a CS-related service branch is pending.
Call flow position: Network notification message sent before the UE continues a CS-oriented restore branch.
Typical state: The UE is already registered and is being notified about a pending CS-related service condition.
Preconditions:
Next likely message: Extended Service Request
Previous message(s): Paging
Next message(s): Extended Service Request, Service Request
Security context: Usually protected because it appears in an existing EMM context.
CS Service Notification
Paging identity OPTIONAL
CLI OPTIONAL
SS code OPTIONAL
LCS indicator OPTIONAL
Read this message from the wider paging and CS fallback context first.
CS Service Notification
Protocol discriminator: EPS mobility management
Security header type: Integrity protected and ciphered
Message type: CS Service Notification
CLI: incoming CS service indication
| IE | Required | Description |
|---|---|---|
Paging identity | Optional | Can help tie the notification to the surrounding paging and service context. |
CLI | Optional | May carry calling-line or related CS notification detail when present. |
Paging identityCan help tie the notification to the surrounding paging and service context.
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.
CLIMay carry calling-line or related CS notification detail when present.
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: CS Service Notification may have signaled an incoming CS-related service condition.
What to inspect: Check paging, CS Service Notification, and the later Extended Service Request.
Next step: Treat the branch as service notification handling before blaming random service-request behavior.
It is the LTE NAS message the network sends to notify the UE about a pending CS-related service branch.
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.