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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

Hex Decimal Cause
0x1 1 Unallocated or unassigned number
0x2 2 No route to specified transit network (Transit Network Identity)
0x3 3 No route to destination
0x4 4 Send special information tone
0x5 5 Misdialed trunk prefix
0x6 6 Channel unacceptable
0x7 7 Call awarded and being delivered in an established channel
0x8 8 Prefix 0 dialed but not allowed
0x9 9 Prefix 1 dialed but not allowed
0xA 10 Prefix 1 not dialed but required
0xB 11 More digits received than allowed, call is proceeding
0x10 16 Normal call clearing
0x11 17 User busy
0x12 18 No user responding
0x13 19 T.301 expired: – User Alerted, No answer from user
0x15 21 Call rejected
0x16 22 Number changed to number in diagnostic field.
0x17 23 Reverse charging rejected
0x18 24 Call suspended
0x19 25 Call resumed
0x1A 26 Non-selected user clearing
0x1B 27 Destination out of order
0x1C 28 Invalid number format or incomplete address
0x1D 29 EKTS facility rejected by network
0x1E 30 Response to STATUS INQUIRY
0x1F 31 Normal, unspecified
0x21 33 Circuit out of order
0x22 34 No circuit/channel available
0x23 35 Destination unattainable
0x24 36 Out of order
0x25 37 Degraded service
0x26 38 Network out of order
0x27 39 Transit delay range cannot be achieved
0x28 40 Throughput range cannot be achieved
0x29 41 Temporary failure
0x2A 42 Switching equipment congestion
0x2B 43 Access information discarded
0x2C 44 Requested circuit channel not available
0x2D 45 Preempted
0x2E 46 Precedence call blocked
0x2F 47 Resource unavailable, unspecified
0x31 49 Quality of service unavailable
0x32 50 Requested facility not subscribed
0x33 51 Reverse charging not allowed
0x34 52 Outgoing calls barred
0x35 53 Outgoing calls barred within CUG
0x36 54 Incoming calls barred
0x37 55 Incoming calls barred within CUG
0x38 56 Call waiting not subscribed
0x39 57 Bearer capability not authorized
0x3A 58 Bearer capability not presently available
0x3F 63 Service or option not available, unspecified
0x41 65 Bearer service not implemented
0x42 66 Channel type not implemented
0x43 67 Transit network selection not implemented
0x44 68 Message not implemented
0x45 69 Requested facility not implemented
0x46 70 Only restricted digital information bearer capability is available
0x4F 79 Service or option not implemented, unspecified
0x51 81 Invalid call reference value
0x52 82 Identified channel does not exist
0x53 83 A suspended call exists, but this call identity does not
0x54 84 Call identity in use
0x55 85 No call suspended
0x56 86 Call having the requested call identity has been cleared
0x57 87 Called user not member of CUG
0x58 88 Incompatible destination
0x59 89 Non-existent abbreviated address entry
0x5A 90 Destination address missing, and direct call not subscribed
0x5B 91 Invalid transit network selection (national use)
0x5C 92 Invalid facility parameter 93 Mandatory information element is missing
0x5D 93 Message type non-existent or not implemented
0x5F 95 Invalid message, unspecified
0x60 96 Mandatory information element is missing
0x61 97 Message type non-existent or not implemented
0x62 98 Message not compatible with call state or message type non-existent or not implemented
0x63 99 Information element nonexistent or not implemented
0x64 100 Invalid information element contents
0x65 101 Message not compatible with call state
0x66 102 Recovery on timer expiry
0x67 103 Parameter non-existent or not implemented – passed on
0x6F 111 Protocol error, unspecified
0x7F 127 Internetworking, unspecified
0x80+ 128 orhigher Proprietary diagnostic code (not necessarily bad). Typically used to pass proprietary control or maintenance messages between multiplexers.
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