- •A 487 SIP error means the call was terminated at the carrier layer before it ever reached a device.
- •Most dialers only track what happens inside their system, leaving the carrier handoff a blind spot.
- •Carrier-layer number flagging, STIR/SHAKEN attestation failures, and high call velocity drive 487 rates up.
- •Getting visibility into 487 rates per number and carrier requires carrier-layer instrumentation, not a dialer fix.
A 487 SIP error means your call was terminated at the carrier layer before it ever reached a device. No ring. No voicemail. Nothing. And in most outbound operations, it never shows up as a problem.
That's where the revenue leak lives.
What does the 487 SIP code actually mean?
SIP - Session Initiation Protocol - is the signaling language that voice networks use to set up and tear down calls. When you dial out, your system sends an INVITE to the carrier network. The carrier responds with a series of codes telling you what happened.
A 200 OK means the call connected at the network layer. A 486 means the line was busy. A 404 means the number doesn't exist.
A 487 - "Request Terminated" - means the call was cancelled before it completed. The session never established. Strictly speaking, the 487 is returned when a pending call is terminated by a CANCEL - most often sent by the dialer itself after giving up on a call that never rang. The question that matters is why it never rang. In many cases, the answer is that the carrier layer or an analytics engine suppressed the call silently: it sat in dead air until the dialer cancelled, and the 487 is the receipt.
The call looks like it went out. Your dialer may log it as an attempt. But a human never heard it ring.
Why isn't your dialer telling you about 487 errors?
Most dialers are designed to track what happens inside their system. They record dials, connections, talk time, dispositions. They report on what they see.
What they don't see is what happens between your system and the carrier. That handoff - where your call leaves your dialer and enters the public voice network - is a blind spot for most contact center operations.
A 487 happens in that gap. The call left your system successfully. Everything looked normal. But it was killed in transit before it could ring.
If you're running a high-volume outbound operation and you've never looked at your 487 rate, you don't know how many dials are being wasted before they reach a single consumer. I've seen operations where 20 - 30% of attempts were dying at the carrier layer. That's not a call center problem. That's a voice network problem.
What is actually causing 487 errors on outbound calls?
The most common cause today is carrier-layer number flagging. Analytics engines - Hiya, First Orion, TNS - evaluate your numbers in real time as calls traverse the network. If a number has been flagged as Spam Likely or blocked by a carrier, the network may terminate the call before it rings. The 487 is the signal that tells you it happened.
STIR/SHAKEN attestation failures can also contribute. Calls that can't be attested at the A-level face higher termination rates at downstream carriers, particularly with the major wireless networks.
Volume patterns matter too. Numbers that dial at extremely high frequency over short windows trigger carrier-side heuristics that accelerate flagging. Once flagged, 487 rates climb. Most operations don't connect those dots until the contact rates have already deteriorated significantly.
What should your operation do about a high 487 rate?
First, get visibility. If your current voice infrastructure doesn't surface 487 rates per number or per carrier, you're flying blind on a meaningful portion of your outbound traffic. This is not something your dialer vendor can solve - it requires carrier-layer instrumentation.
Second, separate the signal from the noise. Not every 487 is a reputation problem. A spike in 487s on a specific carrier on a specific number pool is a data point worth investigating. A uniform low-level 487 rate across all traffic may be normal. The pattern tells you where to focus.
Third, don't rotate numbers blindly. A common response to declining contact rates is to cycle in fresh numbers. That works, temporarily. But if you're not addressing why numbers are getting flagged in the first place - call patterns, volume velocity, STIR/SHAKEN posture - you'll burn through a new pool just as fast.
The 487 rate isn't a curiosity metric. It's one of the most actionable signals in outbound voice. If you're not tracking it, you're not operating with full information on what your voice network is actually doing.
The Bottom Line
Your dialer tells you what happened inside the system. The 487 rate tells you what happened to the carrier network before a human ever picked up. Those are two different things, and most operations only measure one of them.
If you want to know where your answer rates are really going, start with the signal your dialer isn't showing you.
Frequently Asked Questions
What is a 487 SIP error?
A 487 SIP error, formally called "Request Terminated," means a call was cancelled before the session completed. The dialer sends a CANCEL after the call sits in dead air, and the 487 is the receipt confirming the session never established.
Why does a 487 SIP error occur on outbound calls?
The most common cause is carrier-layer number flagging by analytics engines such as Hiya, First Orion, or TNS. When a number is marked as Spam Likely or blocked, the network can terminate the call silently before it ever rings, and the dialer receives a 487 after it cancels the waiting session.
Can STIR/SHAKEN failures contribute to 487 errors?
Yes. Calls that cannot be attested at the A-level face higher termination rates at downstream carriers, particularly with the major wireless networks, which can raise a campaign's overall 487 rate.
Why doesn't my dialer report 487 errors?
Most dialers track only what happens inside their own system: dials, connections, talk time, and dispositions. The handoff between the dialer and the public voice network is a blind spot, and 487s occur in that gap after the call has already left the dialer.
How high a 487 rate is considered a problem?
There is no universal threshold, but a spike in 487s on a specific carrier or number pool is a data point worth investigating. A uniform low-level rate across all traffic may be normal; patterns tied to particular numbers or carriers indicate a reputation or attestation issue.
Does rotating phone numbers fix a 487 problem?
Only temporarily. Cycling in fresh numbers can restore contact rates in the short term, but if the underlying causes, such as call velocity patterns or STIR/SHAKEN posture, are not addressed, the new number pool will be flagged just as quickly.
