Q.850 cause 3 No route to destination
The network handling your call has no path to that destination at all. Common on international, premium and short-code ranges that your trunk is not enabled for, or where an outbound route table has no matching entry. The number may be perfectly valid — it just cannot be reached this way.
What Q.850 cause 3 No route to destination actually means
This is a reachability statement about the destination rather than a statement about the number being wrong or unassigned. Some network in the chain has looked at where the call needs to go and found it has no route there, either because it genuinely does not serve that part of the world or because it has been configured not to. The specification notes the cause is supported on a network-dependent basis, so different carriers use it with different degrees of enthusiasm. RFC 3398 maps it to SIP 404 Not Found.
This cause indicates that the called party cannot be reached because the network through which the call has been routed does not serve the destination desired. This cause is supported on a network-dependent basis.
— ITU-T Q.850 section 6.2.7.1.3
The SIP equivalent of Q.850 cause 3
A gateway translating this cause into SIP reports it as SIP 404 Not Found. The mapping is defined in RFC 3398 section 7.2.4.1.
What causes Q.850 cause 3 on a business phone system
- International dialling not enabled on the trunkCarriers routinely ship new SIP trunks with international calling switched off as a fraud control, and it has to be requested. The first person who tries to call a supplier abroad discovers this, often weeks after go-live.
- A destination barred for fraud reasonsRanges associated with revenue-share fraud — certain satellite, Caribbean and small-nation destinations — are commonly blocked by default across a carrier network. The block is applied to everybody, not just to you.
- No matching entry in the outbound route tableOn an on-premise PBX every outbound pattern needs a route. A number that matches no pattern, or matches a pattern pointing at a trunk that has been decommissioned, produces no route to destination.
- A premium or special range the carrier does not carrySome operators simply do not terminate to certain premium rate or specialised service ranges. The number works from a BT line and fails from your trunk, which is a commercial decision rather than a fault.
How to fix Q.850 cause 3
- Establish whether it is one destination or all of themTry three numbers: a UK landline, a UK mobile and the failing destination. If only the last fails, the issue is destination-specific and belongs with your carrier. If all fail, your outbound routing is broken.
- Check the outbound route table on the PBXConfirm there is a pattern matching the dialled number and that it points at a live trunk. Watch for patterns ordered so that a broader rule catches the call before the correct one does.
- Ask the carrier to enable the destinationMost will lift an international or premium bar on request, sometimes with a deposit or a spend cap. Ask them to confirm in writing which destination groups are open on your account so you are not guessing next time.
- Review your own fraud barring before assuming it is the carrierMany PBX platforms carry their own destination blocks. Check these first — it is a short job and it saves raising a fault against a carrier who is not causing it.
Fixing the underlying problem
This page explains the code. These guides walk through the fix in detail.
Questions about Q.850 cause 3
Why do only international calls fail with cause 3?
Is cause 3 coming from my PBX or my carrier?
Related Q.850 cause values
- Q.850 cause 1Unallocated (unassigned) number
- Q.850 cause 2No route to specified transit network (national use)
- Q.850 cause 34No circuit/channel available
Source. Q.850 cause 3 No route to destination is defined in ITU-T Q.850 section 6.2.7.1.3 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.