Q.850 cause 19 No answer from user (user alerted)

What Q.850 cause 19 means

The phone rang and nobody picked it up. Cause 19 is not a fault — it is the network telling you a human decision was never made. It is worth attention only when it is frequent, which is a staffing, ring-timer or voicemail-routing question rather than a technical one. SIP maps it to 480.

Normal class
Sent by The terminating PBX or a network ring timer
Common

What Q.850 cause 19 No answer from user (user alerted) actually means

The destination was reached, it confirmed the call by alerting, and the caller heard ringing. What never arrived was a connect indication, so after a set period the call was cleared. The specification adds that this cause is not necessarily produced by the signalling procedures themselves but may come from an internal network timer, which is why the timeout length varies between platforms. RFC 3398 maps it to SIP 480 Temporarily Unavailable. Everything about it is normal — the only useful question is what should have happened instead of the call simply ending.

This cause is used when the called party has been alerted but does not respond with a connect indication within a prescribed period of time. NOTE – This cause is not necessarily generated by ITU-T Q.931 procedures but may be generated by internal network timers.
— ITU-T Q.850 section 6.2.7.1.14

The SIP equivalent of Q.850 cause 19

A gateway translating this cause into SIP reports it as SIP 480 Temporarily Unavailable. The mapping is defined in RFC 3398 section 7.2.4.1.

What causes Q.850 cause 19 on a business phone system

Nobody was at the deskThe unremarkable explanation, and usually the right one. Someone was in a meeting, at lunch or away from their phone. No configuration change makes this go away; a no-answer destination makes it harmless.
No voicemail or overflow destination is configuredWhen an extension has nowhere to send unanswered calls, the ring timer simply expires and the caller is dropped. This is the single most common reason cause 19 shows up as a business problem rather than a statistic.
The ring timer is too short for the environmentFour or five rings is about right for a desk phone. In a workshop, a shop floor or anywhere people move around, a timer set for an office worker cuts callers off before anyone can reach a handset.
A hunt group giving each member too little timeSequential ring strategies divide the overall timeout between members. With enough members, each gets only a couple of rings, and the call can pass through the entire group without anyone realistically able to answer.
Out-of-hours calls with no out-of-hours routeCalls arriving at seven in the morning or on a Saturday ring an empty office until the timer expires. Check whether your cause 19 records cluster outside working hours before treating it as a daytime problem.

How to fix Q.850 cause 19

Give every unanswered call somewhere to goSet a no-answer destination on each extension and group — voicemail, a colleague, a mobile or a shared mailbox. Then no caller is ever simply dropped, and you have a record of the attempt.
Set the ring timer to suit the roleLengthen it where people are away from their desks, shorten it where you would rather callers reached voicemail quickly. Test by ringing the extension and counting how long you would tolerate as a customer.
Build proper out-of-hours routingDefine your opening hours in the system and route calls outside them to a greeting, an emergency mobile or voicemail. This alone removes a large slice of unanswered calls from the report.
Reconsider the hunt group strategyRing-all reaches everyone immediately but is disruptive; sequential is calmer but slower. If calls are passing through the whole group unanswered, either shorten the group or move to ring-all.
Report on missed calls and act on the numbersTrack unanswered calls by hour and by group. If they cluster in predictable windows, the answer is cover at those times, which is a rota decision your phone system cannot make for you.

Fixing the underlying problem

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

Questions about Q.850 cause 19

Does cause 19 mean the phone actually rang?

Yes. The name of the cause includes user alerted for exactly that reason — the destination confirmed it was ringing before the call timed out. If you need to know whether a phone rang at all, this cause is your evidence that it did.

How do we stop calls ending in cause 19?

You cannot stop people being away from their desks, but you can stop callers being dropped. Give every extension and group a no-answer destination, and the call ends in voicemail or with a colleague instead of in silence.

Is cause 19 counted as a missed call?

In most reporting tools, yes. That is usually correct for a direct dial, but be careful with hunt groups, where legs to members who did not answer can inflate the figure even though the call was picked up by somebody else.

Related Q.850 cause values

Source. Q.850 cause 19 No answer from user (user alerted) is defined in ITU-T Q.850 section 6.2.7.1.14 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