| Protocol | ims | Network | 5G and LTE |
|---|---|---|---|
| Spec | RFC 3261 / 3GPP TS 24.229 | Spec Section | SIP 180 Ringing provisional response and IMS alerting |
| Direction | IMS network -> UE | Message Type | SIP provisional response |
| Full message name | IMS SIP 180 Ringing |
|---|---|
| Protocol | IMS |
| Technology | 5G and LTE |
| Common deployment | VoNR and VoLTE |
| Direction | IMS network -> UE |
| Interface | Gm with onward IMS routing |
| Signaling bearer / channel | IMS SIP signaling / Provisional session-setup response |
| Typical trigger | The terminating side is ringing after receiving INVITE. |
| Main purpose | Signals alerting progress before final answer so the originating side can present ringing indication. |
| Main specification | RFC 3261 / 3GPP TS 24.229, SIP 180 Ringing provisional response and IMS alerting |
| Release added | See specification history |
| Procedures where used | IMS Mobile Originated Call, IMS Mobile Terminated Call, VoNR Call Setup, VoLTE Call Setup |
180 Ringing shows that the terminating side is being alerted for the session request.
Signals alerting progress before final answer so the originating side can present ringing indication.
180 Ringing means the far side is being alerted, not that the call is already connected.
Previous message(s): IMS SIP INVITE, 100 Trying
Next message(s): 183 Session Progress, 200 OK
Security context: Uses the same protected IMS signaling path as the INVITE transaction.
SIP/2.0 180 Ringing
Via:
From:
To:
Call-ID:
CSeq:
Contact: OPTIONAL
Content-Length: 0
This is SIP response syntax rather than ASN.1.
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP ue.example.net;branch=z9hG4bK-inv1
From: <sip:alice@example.net>;tag=mo1
To: <sip:bob@example.net>;tag=term1
Call-ID: call-001@example.net
CSeq: 1 INVITE
Content-Length: 0
| IE | Required | Description |
|---|---|---|
Status-Line | Yes | Shows the 180 Ringing response code. |
To tag | Optional | Often marks the early dialog branch. |
Call-ID | Yes | Correlates ringing with the original INVITE. |
Status-LineShows the 180 Ringing response code.
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.
To tagOften marks the early dialog 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.
Call-IDCorrelates ringing with the original INVITE.
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: Alerting started, but later answer, media, or policy handling failed.
What to inspect: Read 180 Ringing together with later 183, 200 OK, or final failure responses.
Next step: Follow the alerting branch until the final result is visible.
It means the called side is being alerted and the originating side can present ringing indication.
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.