Q.850 cause 103 Parameter non-existent or not implemented – passed on

What Q.850 cause 103 means

This is a diagnostic note more than a call failure. Signalling contained a parameter the equipment did not recognise, so it ignored that parameter and, being a transit point, passed it on unchanged. Calls carrying cause 103 have often completed perfectly well. RFC 3398 publishes no SIP mapping for it, and in most cases no action is needed.

Protocol error class
Sent by An intermediate switch or gateway that parsed the message
Rare

What Q.850 cause 103 Parameter non-existent or not implemented – passed on actually means

The important word in the official name is passed on. Rather than rejecting a message it did not fully understand, the equipment chose to be tolerant: it skipped the unrecognised parameter and forwarded the message intact so that a later element, which may well understand it, still gets the chance. This is deliberate design for interworking between generations of equipment, and it means the cause is telling you about the equipment's parsing rather than about the outcome of the call. RFC 3398 lists no SIP translation for it, which is consistent with it not being a failure.

This cause indicates that the equipment sending this cause has received a message which includes parameters not recognized because the parameters are not defined or are defined but not implemented by the equipment sending the cause. The cause indicates that the parameter(s) was ignored. In addition, if the equipment sending this cause is an intermediate point, then this cause indicates that the parameter(s) was passed on unchanged.
— ITU-T Q.850 section 6.2.7.6.8

The SIP equivalent of Q.850 cause 103

RFC 3398 publishes no recommended SIP status for this cause. It maps a subset of cause values only, and states that a cause outside that subset should default to 500 Server Internal Error. Seeing this cause reach a SIP leg unchanged usually means something in the path passed it through without translating it.

What causes Q.850 cause 103 on a business phone system

Mixed protocol variants across an interconnectNational and international signalling variants define different optional parameters. Each side sends what its own variant permits, and the other side notes what it did not recognise.
A newer feature parameter meeting older equipmentParameters added in later specification revisions are unknown to kit that predates them. The older element ignores them by design, which is exactly the behaviour this cause reports.
Vendor-specific parameters in the signallingManufacturers add proprietary information that only their own equipment reads. Anything else in the path notes it and moves on.
A firmware update on one side onlyUpgrading one element can introduce parameters the rest of the path has not seen before. The timing is the giveaway: this cause starts appearing the day after a change.

How to fix Q.850 cause 103

Check whether anything actually failed before investigatingLook at whether the calls carrying this cause connected and lasted a sensible length. If they did, the sensible response is to note it and spend the time elsewhere.
Record which element reported it and in which directionIf you are chasing a genuine interworking bug, that pairing is the useful part. It tells you where a parameter is being dropped from the chain of understanding.
Establish whether the ignored parameter matteredSome parameters carry presentation or charging information that quietly affects behaviour, such as a caller identity not displaying as intended. Work backwards from the visible symptom rather than from the cause code.
Align the protocol profile only if there is a real symptomAgreeing the variant with the carrier fixes it, but changing an interconnect profile is not a trivial exercise. Weigh that against a cause that in most cases is purely informational.

Fixing the underlying problem

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

Questions about Q.850 cause 103

Is cause 103 a fault?

Usually not. It records that a parameter was unrecognised and ignored while the message continued on its way, so it is best read as a note about interworking rather than as a reason a call failed.

Which SIP response corresponds to cause 103?

RFC 3398 publishes none, which is unsurprising for a cause that does not describe a failed call. The RFC's general fallback for unlisted causes is 500 Server Internal Error, but that would be a poor description of what happened here.

Should I ask my carrier about cause 103?

Only if you have a symptom to attach to it, such as caller identity or charging information not arriving as expected. Raising it on its own tends to produce a long conversation about a message that was handled correctly.

Related Q.850 cause values

Source. Q.850 cause 103 Parameter non-existent or not implemented – passed on is defined in ITU-T Q.850 section 6.2.7.6.8 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