SIP 180 Ringing
The called user agent is alerting the user.
1xx Provisional · RFC 3261 · Answer to OPTIONS: Not a final answer. The check waits for the final response.
What SIP 180 means
180 Ringing tells the caller that the INVITE reached a device that is now alerting its user: a desk phone ringing, a softphone flashing, or a queue that has taken the call and is waiting for an agent. It is a provisional response, so the call isn't set up yet, but it is the first answer that proves the call reached the far end.
180 is only sent for INVITE. It usually carries a To tag, which starts an early dialog. Without an SDP body the caller plays its own ringback tone; with one, the caller may play media from the far end instead. A call can receive several 180s when a proxy forks it to more than one device.
Example response
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP 198.51.100.11:5060;branch=z9hG4bK-180-c3
From: <sip:+[email protected]>;tag=41aa
To: <sip:+[email protected]>;tag=r8812
Call-ID: [email protected]
CSeq: 21 INVITE
Contact: <sip:+[email protected]:5060>
Content-Length: 0Common causes of SIP 180
- The callee's phone is ringing and nobody has picked up yet, which is exactly what 180 reports.
- A queue or hunt group sent 180 while it waits for a free agent, so callers hear ringing for as long as the queue holds them.
- The 180 carried SDP and the caller waits for far-end ringback that never arrives, so the line sounds dead.
- The 180 is lost on the way back because a firewall or NAT drops it, and the caller hears silence until the final response.
How to fix SIP 180
- If callers hear silence instead of ringing, check whether the 180 has an SDP body and whether that media reaches them.
- Check the no-answer timers on the PBX, the SBC and the carrier, and make sure the shortest one is long enough for your queue.
- Look for several 180s with different To tags: the call was forked, and each tag is a separate device ringing.
- If no 180 reaches the caller, trace it hop by hop; responses follow the Via path back, so one broken Via loses it.
SIP 180 as an answer to OPTIONS
A 180 is never a real answer to OPTIONS, because OPTIONS doesn't ring anything. If one arrived, PingVo would treat it like any provisional response and keep waiting for a final one; with none before the timeout the probe counts as no answer. To see whether calls reach a ringing device, you need a real test call.
Questions about SIP 180
What is the difference between SIP 180 and 183?
180 says the far end is alerting. 183 says there is progress to report, usually early media such as an announcement or network ringback. Both are provisional, and either can carry SDP.
Why does a call ring forever and never connect?
The far end is alerting but no one answers, or a queue keeps the call ringing while it waits for an agent. Eventually something gives up: a no-answer timer sends CANCEL, or the far end sends a final error.
Is 180 Ringing a sign that the line works?
It shows that signalling reached a device. It doesn't prove that audio will flow, or that the right IVR will answer once the call connects.