Q.850 cause 47 Resource unavailable, unspecified
A resource somewhere ran out and the equipment could not say which one. Q.850 permits cause 47 only when no other cause in the resource-unavailable class applies, so the class is the message: something was exhausted, as opposed to barred, unreachable or misconfigured. Useful diagnosis starts with finding out which element generated it.
What Q.850 cause 47 Resource unavailable, unspecified actually means
This is the catch-all of the resource-unavailable class, and what it tells you is as much about the equipment as about the call. The sender knew enough to classify the problem as a shortage of something but not enough to name it, which in practice happens for two quite different reasons: a genuinely unclassifiable internal shortage, or a more specific cause that lost its detail crossing a boundary between networks. RFC 3398 maps it to 503 Service Unavailable in common with the rest of its class.
This cause is used to report a resource unavailable event only when no other cause in the resource unavailable class applies.
— ITU-T Q.850 section 6.2.7.2.10
The SIP equivalent of Q.850 cause 47
A gateway translating this cause into SIP reports it as SIP 503 Service Unavailable. The mapping is defined in RFC 3398 section 7.2.4.1.
What causes Q.850 cause 47 on a business phone system
- A specific cause flattened at an interworking pointA gateway that receives a cause it cannot represent may substitute the class catch-all rather than drop the information entirely. The real reason still exists, but it is one hop further back than the record you are reading.
- Media resources exhausted rather than call pathsTranscoders, conference bridges, announcement players and recording ports are finite and separate from channel count. A system with plenty of free channels can still refuse calls because it has run out of the resource needed to process them.
- Session or licence limits on an SBC or PBXSoftware licences frequently cap concurrent sessions independently of what the trunk supports. Hitting a licence ceiling is a resource shortage in the strict sense and often has no more specific code.
- A vendor using 47 as its internal defaultSome implementations return this for a range of internal failures rather than mapping each one. Where that is the case, the number on its own carries little information and the vendor log is the only way forward.
How to fix Q.850 cause 47
- Find out which element generated the causeQ.850 carries a location alongside the cause value, indicating whether it came from the user, the private network, the local public network or a transit network. That field narrows the search more than the cause number does.
- Check the finite resources that are not channelsLook at transcoding sessions, recording channels, conference ports and announcement players at the time of failure. These run out quietly and rarely appear on the dashboard people watch.
- Compare against licensed session countsRead the licensed maximum from the platform and compare it with peak concurrent sessions. A shortfall here produces failures that look like network problems but are purely commercial.
- Correlate with load to separate the two explanationsIf failures track busy periods, treat it as genuine exhaustion and size accordingly. If they are scattered with no relation to load, the flattened-cause explanation is more likely and the carrier needs to trace it.
Fixing the underlying problem
This page explains the code. These guides walk through the fix in detail.
Questions about Q.850 cause 47
How is cause 47 different from cause 42?
Can I fix cause 47 myself?
Related Q.850 cause values
- Q.850 cause 38Network out of order
- Q.850 cause 41Temporary failure
- Q.850 cause 42Switching equipment congestion
Source. Q.850 cause 47 Resource unavailable, unspecified is defined in ITU-T Q.850 section 6.2.7.2.10 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.