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Q.850 cause codes

A Q.850 cause value is the reason a call ended, reported as a number between 1 and 127. Find yours below, or search for it directly — including in the forms your phone system prints it, such as "cause 34" or "hangup cause 17".

Normal class

Resource unavailable class

Service or option unavailable class

Service or option not implemented class

Invalid message class

Protocol error class

Interworking class

Every other Q.850 cause value

These are the remaining cause values in Q.850. Most are seen only inside a carrier network or concern a gateway's own circuit handling rather than anything you can act on, so we have not written them up — but the specification defines each one, so its official definition is reproduced here in full.

CodeOfficial nameWhat the specification saysDefined in
Q.850 cause 4Send special information toneThis cause indicates that the called party cannot be reached for reasons that are of a long-term nature and that the special information tone should be returned to the calling party.ITU-T Q.850 section 6.2.7.1.4
Q.850 cause 5Misdialled trunk prefix (national use)This cause indicates the erroneous inclusion of a trunk prefix in the called party number.ITU-T Q.850 section 6.2.7.1.5
Q.850 cause 7Call awarded and being delivered in an established channelThis cause indicates that the user has been awarded the incoming call, and that the incoming call is being connected to a channel already established to that user for similar calls (e.g., packet-mode ITU-T X.25 virtual calls).ITU-T Q.850 section 6.2.7.1.7
Q.850 cause 8Pre-emptionThis cause indicates that the call is being pre-empted.ITU-T Q.850 section 6.2.7.1.8
Q.850 cause 9Pre-emption – circuit reserved for reuseThis cause indicates that the call is being pre-empted and the circuit is reserved for reuse by the pre-empting exchange.ITU-T Q.850 section 6.2.7.1.9
Q.850 cause 13Call completed elsewhereWhen the S-CSCF has forked an initial INVITE request, and it has received a 2xx response associated with one of the early dialogues, the S-CSCF shall in each CANCEL request it generates insert a Reason header field with a "SIP" protocol header field parameter value, a "200" cause header field parameter value, and a "Call completed elsewhere" text header field parameter value, as specified in [RFC 3326].ITU-T Q.850 section 6.2.7.1.10
Q.850 cause 25Exchange – routing errorThis cause indicates that the destination indicated by the user cannot be reached, because an intermediate exchange has released the call due to reaching a limit in executing the hop counter procedure. This cause is generated by an intermediate node, which when decrementing the hop counter value, gives the result 0.ITU-T Q.850 section 6.2.7.1.19
Q.850 cause 39Permanent frame mode connection out of serviceThis cause is included in a STATUS message to indicate that a permanently established frame mode connection is out of service (e.g., due to equipment or section failure) (see Annex A of [ITU-T Q.933]).ITU-T Q.850 section 6.2.7.2.3
Q.850 cause 40Permanent frame mode connection operationalThis cause is included in a STATUS message to indicate that a permanently established frame mode connection is operational and capable of carrying user information (see Annex A of [ITU-T Q.933]).ITU-T Q.850 section 6.2.7.2.4
Q.850 cause 43Access information discardedThis cause indicates that the network could not deliver access information to the remote user as requested, i.e., user-to-user information, low layer compatibility, high layer compatibility, or sub-address, as indicated in the diagnostic. It is noted that the particular type of access information discarded is optionally included in the diagnostic.ITU-T Q.850 section 6.2.7.2.7
Q.850 cause 46Precedence call blockedThis cause indicates that there are no pre-emptable circuits or that the called user is busy with a call of equal or higher pre-emptable level.ITU-T Q.850 section 6.2.7.2.9
Q.850 cause 49Quality of service not availableThis cause is used to report that the requested Quality of service, as defined in [ITU-T X.213], cannot be provided (e.g., throughput or transit delay cannot be supported).ITU-T Q.850 section 6.2.7.3.1
Q.850 cause 53Outgoing calls barred within CUGThis cause indicates that although the calling party is a member of the CUG for the outgoing CUG call, outgoing calls are not allowed for this member of the CUG.ITU-T Q.850 section 6.2.7.3.3
Q.850 cause 62Inconsistency in designated outgoing access information andsubscriber class This cause indicates that there is an inconsistency in the designated outgoing access information and subscriber class.ITU-T Q.850 section 6.2.7.3.7
Q.850 cause 66Channel type not implementedThis cause indicates that the equipment sending this cause does not support the channel type requested.ITU-T Q.850 section 6.2.7.4.2
Q.850 cause 69Requested facility not implementedThis cause indicates that the equipment sending this cause does not support the requested supplementary service.ITU-T Q.850 section 6.2.7.4.3
Q.850 cause 81Invalid call reference valueThis cause indicates that the equipment sending this cause has received a message with a call reference which is not currently in use on the user-network interface.ITU-T Q.850 section 6.2.7.5.1
Q.850 cause 82Identified channel does not existThis cause indicates that the equipment sending this cause has received a request to use a channel not activated on the interface for a call. For example, if a user has subscribed to those channels on a primary rate interface numbered from 1 to 12 and the user equipment or the network attempts to use channels 13 to 23, this cause is generated.ITU-T Q.850 section 6.2.7.5.2
Q.850 cause 83A suspended call exists, but this call identity does notThis cause indicates that a call resume has been attempted with a call identity which differs from that in use for any presently suspended call(s).ITU-T Q.850 section 6.2.7.5.3
Q.850 cause 84Call identity in useThis cause indicates that the network has received a call suspended request containing a call identity (including the null call identity) which is already in use for a suspended call within the domain of interfaces over which the call might be resumed.ITU-T Q.850 section 6.2.7.5.4
Q.850 cause 85No call suspendedThis cause indicates that the network has received a call resume request containing a call identity information element which presently does not indicate any suspended call within the domain of interfaces over which calls may be resumed.ITU-T Q.850 section 6.2.7.5.5
Q.850 cause 86Call with the requested call identity has been clearedThis cause indicates that the network has received a call resume request containing a call identity information element indicating a suspended call that has in the meantime been cleared while suspended (either by network timeout or by the remote user).ITU-T Q.850 section 6.2.7.5.6
Q.850 cause 90Non-existent CUGThis cause indicates that the specified CUG does not exist.ITU-T Q.850 section 6.2.7.5.9
Q.850 cause 91Invalid transit network selection (national use)This cause indicates that a transit network identification was received which is of an incorrect format as defined in Annex C of [ITU-T Q.931].ITU-T Q.850 section 6.2.7.5.10
Q.850 cause 95Invalid message, unspecifiedThis cause is used to report an invalid message event only when no other cause in the invalid message class applies.ITU-T Q.850 section 6.2.7.5.11
Q.850 cause 96Mandatory information element is missingThis cause indicates that the equipment sending this cause has received a message which is missing an information element which must be present in the message before that message can be processed.ITU-T Q.850 section 6.2.7.6.1
Q.850 cause 97Message type non-existent or not implementedThis cause indicates that the equipment sending this cause has received a message with a message type it does not recognize either because this is a message not defined or defined but not implemented by the equipment sending this cause.ITU-T Q.850 section 6.2.7.6.2
Q.850 cause 98Message not compatible with call state or message type non-existentor not implemented This cause indicates that the equipment sending this cause has received a message so that the procedures do not indicate that this is a permissible message to receive while in the call state, or a STATUS message was received indicating an incompatible call state.ITU-T Q.850 section 6.2.7.6.3
Q.850 cause 99Information element/parameter non-existent or not implementedThis cause indicates that the equipment sending this cause has received a message which includes information element(s)/parameter(s) not recognized because the information element identifier(s)/parameter name(s) is not defined or defined but not implemented by the equipment sending the cause. This cause indicates that the information element(s)/parameter(s) has been discarded. However, the information element is not required to be present in the message in order for the equipment sending the cause to process the message.ITU-T Q.850 section 6.2.7.6.4
Q.850 cause 100Invalid information element contentsThis cause indicates that the equipment sending this cause has received an information element which it has implemented; however, one or more fields in the information element are coded in such a way which has not been implemented by the equipment sending this cause.ITU-T Q.850 section 6.2.7.6.5
Q.850 cause 101Message not compatible with call stateThis cause indicates that a message has been received which is incompatible with the call state.ITU-T Q.850 section 6.2.7.6.6
Q.850 cause 110Message with unrecognized parameter discardedThis cause indicates that the equipment sending this cause has discarded a received message which includes a parameter that is not recognized.ITU-T Q.850 section 6.2.7.6.9

Source. Cause values, official names and definitions are taken from ITU-T Recommendation Q.850 (10/2018). The SIP response each cause maps to is from RFC 3398 section 7.2.4.1, which publishes a recommended mapping for some causes but not all; where no mapping is published we say so rather than infer one. Causes and fixes are our own, from supporting UK business phone systems.

Troubleshooting guides

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

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