Q.850 cause 22 Number changed

What Q.850 cause 22 means

The number was in service and is not any more — the network knows it changed rather than simply not existing. Where a carrier supports it, the replacement number can travel in the diagnostic field. Many UK carriers return cause 1 instead. SIP equivalent is 410 Gone.

Normal class
Sent by The terminating network responsible for the old number
Occasional

What Q.850 cause 22 Number changed actually means

This cause carries a specific piece of knowledge that cause 1 does not: the network is aware the number used to be assigned and no longer is, and it may know what replaced it. The specification allows the new number to be included in the diagnostic field, and states plainly that a network which does not support this cause must fall back to cause 1. That fallback is why a genuinely renumbered line often reports as unallocated in UK CDRs. RFC 3398 maps it to SIP 410 Gone, which conveys the same idea of a resource that existed and has been withdrawn.

This cause is returned to a calling party when the called party number indicated by the calling party is no longer assigned. The new called party number may optionally be included in the diagnostic field. If a network does not support this cause value, cause No. 1, Unallocated (unassigned) number, shall be used.
— ITU-T Q.850 section 6.2.7.1.17

The SIP equivalent of Q.850 cause 22

A gateway translating this cause into SIP reports it as SIP 410 Gone. The mapping is defined in RFC 3398 section 7.2.4.1.

What causes Q.850 cause 22 on a business phone system

A business renumbered when it moved or changed providerWhere a company took new numbers instead of porting the old ones, the original range holder may keep a change record for a period before releasing the numbers back into the pool.
A number ported away with a stale route left behindIf the losing carrier does not withdraw its route promptly, calls arrive at the old network which knows the number has gone. That is exactly the condition this cause describes.
A DID reclaimed after a cancellationCancel a number and the range holder takes it back. For a while the network still associates it with the change, and only later does it revert to plain unallocated.
A line ceased during PSTN migrationAnalogue and ISDN services being retired ahead of the switch-off leave behind numbers that were live for decades. Callers working from old records keep dialling them long after the cease completes.

How to fix Q.850 cause 22

Look in the diagnostic field for a replacement numberWhere the network supports it, the new number is right there. That is the whole point of this cause value, and it saves you searching for a business that has quietly renumbered.
Update the number wherever it is storedCRM records, supplier lists, website contact pages, email signatures and printed material all outlive the number itself. Fix the source rather than the individual failed call.
If it is your own number, chase the portAsk the gaining carrier to confirm the port completed and the losing carrier to confirm the route has been withdrawn. Callers seeing this cause on a number you now own means the old route is still answering.
Keep an announcement on a number you are retiringRather than letting a number die, hold it for a period with a recorded message giving the new one. It costs little and it preserves the callers who only have the old number.

Fixing the underlying problem

This page explains the code. These guides walk through the fix in detail.

Questions about Q.850 cause 22

Does cause 22 tell me the new number?

Sometimes. The specification permits the replacement number to be carried in the diagnostic field, but it is optional and many networks omit it. If it is present your call logging tool may not display it, so check the raw trace before concluding it was not sent.

What is the difference between cause 22 and cause 1?

Cause 22 says the number was assigned and has changed. Cause 1 says it is not assigned, without any history. Because networks that do not support cause 22 must use cause 1 instead, a changed number frequently reports as unallocated in practice.

We ported our number and callers now get cause 22. What went wrong?

The old carrier is still answering for the number and telling callers it has gone. Raise it with the gaining provider, quoting example calls, and ask them to confirm with the losing carrier that the route has been properly withdrawn.

Related Q.850 cause values

Source. Q.850 cause 22 Number changed is defined in ITU-T Q.850 section 6.2.7.1.17 and registered in the ITU-T Recommendation Q.850 (10/2018). The causes and fixes above are drawn from our own experience supporting UK business phone systems.

All Call hangup causes (Q.850) codes