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Q.931 CauseCodes

Author’s note:  This article supports our legacy products.  At Inventive Labs, after two decades of providing telephony tools, we never stop supporting those who rely on our products to run their businesses.  We no longer recommend Dialogic. This article is for our customers who are using legacy equipment. For more information about these legacy products and where we are today, read  Ditch Dialogic & Convert to Voice Elements.

Q.931 was designed for ISDN call establishment, maintenance, and release of network connections between two DTEs on the ISDN D channel. Q.931 has more recently been used as part of the VoIP Call Causes as shown below. In troubleshooting, the code standards below may be helpful.

Message examples

  • SETUP (indicating the establishment of a connection)
  • CALL PROCEEDING (indicating that the call is being processed by the destination terminal)
  • ALERTING (tells the calling party that the destination terminal is ringing)
  • CONNECT (sent back to the calling party indicating that the intended destination has answered the call)
  • DISCONNECT (sent to indicate a request to terminate the connection, by the end that seeks to terminate)
  • RELEASE (sent in response to the disconnect request indicating that the call is to be terminated).
  • RELEASE COMPLETE (sent by the receiver of the release to complete the handshake).

Disconnect causes

0x11Unallocated or unassigned number
0x22No route to specified transit network (Transit Network Identity)
0x33No route to destination
0x44Send special information tone
0x55Misdialed trunk prefix
0x66Channel unacceptable
0x77Call awarded and being delivered in an established channel
0x88Prefix 0 dialed but not allowed
0x99Prefix 1 dialed but not allowed
0xA10Prefix 1 not dialed but required
0xB11More digits received than allowed, call is proceeding
0x1016Normal call clearing
0x1117User busy
0x1218No user responding
0x1319T.301 expired: – User Alerted, No answer from user
0x1521Call rejected
0x1622Number changed to number in diagnostic field.
0x1723Reverse charging rejected
0x1824Call suspended
0x1925Call resumed
0x1A26Non-selected user clearing
0x1B27Destination out of order
0x1C28Invalid number format or incomplete address
0x1D29EKTS facility rejected by network
0x1E30Response to STATUS INQUIRY
0x1F31Normal, unspecified
0x2133Circuit out of order
0x2234No circuit/channel available
0x2335Destination unattainable
0x2436Out of order
0x2537Degraded service
0x2638Network out of order
0x2739Transit delay range cannot be achieved
0x2840Throughput range cannot be achieved
0x2941Temporary failure
0x2A42Switching equipment congestion
0x2B43Access information discarded
0x2C44Requested circuit channel not available
0x2E46Precedence call blocked
0x2F47Resource unavailable, unspecified
0x3149Quality of service unavailable
0x3250Requested facility not subscribed
0x3351Reverse charging not allowed
0x3452Outgoing calls barred
0x3553Outgoing calls barred within CUG
0x3654Incoming calls barred
0x3755Incoming calls barred within CUG
0x3856Call waiting not subscribed
0x3957Bearer capability not authorized
0x3A58Bearer capability not presently available
0x3F63Service or option not available, unspecified
0x4165Bearer service not implemented
0x4266Channel type not implemented
0x4367Transit network selection not implemented
0x4468Message not implemented
0x4569Requested facility not implemented
0x4670Only restricted digital information bearer capability is available
0x4F79Service or option not implemented, unspecified
0x5181Invalid call reference value
0x5282Identified channel does not exist
0x5383A suspended call exists, but this call identity does not
0x5484Call identity in use
0x5585No call suspended
0x5686Call having the requested call identity has been cleared
0x5787Called user not member of CUG
0x5888Incompatible destination
0x5989Non-existent abbreviated address entry
0x5A90Destination address missing, and direct call not subscribed
0x5B91Invalid transit network selection (national use)
0x5C92Invalid facility parameter 93 Mandatory information element is missing
0x5D93Message type non-existent or not implemented
0x5F95Invalid message, unspecified
0x6096Mandatory information element is missing
0x6197Message type non-existent or not implemented
0x6298Message not compatible with call state or message type non-existent or not implemented
0x6399Information element nonexistent or not implemented
0x64100Invalid information element contents
0x65101Message not compatible with call state
0x66102Recovery on timer expiry
0x67103Parameter non-existent or not implemented – passed on
0x6F111Protocol error, unspecified
0x7F127Internetworking, unspecified
0x80+128 orhigherProprietary diagnostic code (not necessarily bad). Typically used to pass proprietary control or maintenance messages between multiplexers.
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