SIP 6xx codes indicate global failures.
Unlike client or server errors (4xx or 5xx), these responses mean that no other destination is available or willing to accept the call, even if the request is retried elsewhere.
These messages often reflect a final decision made by the called party or their system, and there's usually no point in retrying the same route.
If your outbound traffic often results in 6xx codes, it may signal poor routing quality, caller ID issues, or reputation problems. If so, your provider might be holding you back.
Too many global rejections?
With Voyced’s trusted caller ID setup and high-quality termination routes, you reduce the risk of 6xx failures right from the start.
Avoid SIP call rejections with Voyced
What do 6xx Errors Mean?
600 – Busy Everywhere
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All reachable destinations are busy, and the system knows no fallback (e.g. voicemail) is available.
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Unlike 486 Busy Here, which is local, 600 applies across all options.
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May indicate:
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Full queues
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No agents available
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No call forwarding configured
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603 – Decline
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The call was rejected, not because of technical reasons, but due to the recipient’s choice.
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Common causes:
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Manual call rejection
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“Do not disturb” active
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Blocklists
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It also signals no alternative endpoints are willing to take the call.
604 – Does Not Exist Anywhere
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The SIP proxy or server is certain that the destination user does not exist.
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Different from 404, which can mean “not found here”.
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Based on authoritative databases or full system knowledge.
606 – Not Acceptable
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The session parameters were rejected even though the SIP endpoint was reached.
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Reasons might include:
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Unsupported codecs
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Incompatible media types
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Invalid addressing methods (e.g. IPv6-only endpoint)
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If you see frequent 606s, double-check your codec settings, particularly for video or fax.
607 – Unwanted (RFC 8197)
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The called party actively marked the call as unwanted, often via a spam-blocking feature.
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Important in spam and robocall detection systems.
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Future calls from your Caller ID will likely also be rejected.
608 – Rejected
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The call was rejected by a machine or intermediary process (not a person).
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Often used in spam-prevention or fraud detection layers.
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RFC 8688 requires a
Call-Infoheader to explain the reason and optionally include a jCard for dispute follow-up. -
Repeated 608s may reflect Caller ID reputation issues or improper CLI settings.
Don’t let global SIP failures stop your business
Some global failures can’t be avoided, but many result from:
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Poor caller ID management
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Low trust score on spam filters
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Unstable call routing via cheap VoIP routes
If you’re relying on cut-price SIP trunks or a provider with weak international coverage, you're more likely to hit a wall.
✅ Switch to Voyced for reliable, trusted Business VoIP
With Voyced, you benefit from:
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A-Z termination with Premium Plus quality
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Full coverage and trusted routes across 165+ countries.
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Less chance of rejections, more answered calls.
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Proper Caller ID management
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We help you configure and validate your caller ID so calls aren't flagged.
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Free Hosted IPPBX
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A robust, secure system to manage call flows, routing, IVR, voicemail and more.
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Low-latency infrastructure
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Georedundant SIP setup and secure protocols like SRTP and TLS supported.
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Support that partners with you
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We help resolve issues and fine-tune your setup, not just point to documentation.
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If your calls are ending in 6xx codes too often…
Let’s find a better path together.
✅ Talk to Voyced
We’ll help you make every call count.
Last updated: 01/04/2025
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All information provided is copyrighted and purely informative in nature. It is maintained by Voyced with the greatest of care using reliable sources only.
Given the fast evolution of the telecom sector, Voyced does not offer any guarantee about the accuracy and completeness of the information offered.
We explicitly do not give anyone permission to use this information in any other way than to inform themselves about what (legal) requirements there may be and they need to comply with when registering Services and/or DIDs with Voyced.
