| Decimal Value | Hex Value | Cause | Diagnostics | Explanation |
| 1 | 01 | Unallocated ( unassigned ) number | Note 10 | The ISDN number was sent to the switch in the correct format; however, the number is not assigned to any destination equipment. |
| 2 | 02 | No route to specified transit network | Transit network identity (Note 9) | The ISDN exchange is asked to route the call through an unrecognized intermediate network. |
| 3 | 03 | No route to destination | Note 10 | The call was routed through an intermediate network that does not serve the destination address. |
| 6 | 06 | Channel unacceptable | | The service quality of the specified channel is insufficient to accept the connection. |
| 7 | 07 | Call awarded and being delivered in an established channel | | The user is assigned an incoming call that is being connected to an already-established call channel. |
| 16 | 10 | Normal call clearing | Note 10 | Normal call clearing has occurred. |
| 17 | 11 | User busy | | The called system acknowledges the connection request but is incapable of accepting the call because all B channels are in use. |
| 18 | 12 | No user responding | | The connection cannot be completed because the destination does not respond to the call. |
| 19 | 13 | No answer from user (user alerted) | | The destination responds to the connection request but fails to complete the connection within the prescribed time. The problem is at the remote end of the connection. |
| 21 | 15 | Call rejected | Note 10; user supplied diagnostic (Note 4) | The destination is capable of accepting the call, but it rejected the call for an unknown reason. |
| 22 | 16 | Number changed | | The ISDN number used to set up the call is not assigned to any system. |
| 26 | 1A | Nonselected user clearing | | The destination is capable of accepting the call, but it rejected the call because it was not assigned to the user. |
| 27 | 1B | Designation out of order | | The destination cannot be reached because the interface is not functioning correctly and a signaling message cannot be delivered. This might be a temporary condition, but it could last for an extended period of time. For example, the remote equipment might be turned off. |
| 28 | 1C | Invalid number format | | The connection could not be established because the destination address was presented in an unrecognizable format or because the destination address was incomplete. |
| 29 | 1D | Facility rejected | Facility identification (Note 1) | The facility requested by the user cannot be provided by the network. |
| 30 | 1E | Response to STATUS ENQUIRY | | The status message was generated in direct response to the previous receipt of a status inquiry message. |
| 31 | 1F | Normal, unspecified | | Reports the occurrence of a normal event when no standard cause applies. No action is required. |
| 34 | 22 | No circuit/channel available | | The connection cannot be established because no appropriate channel is available to take the call. |
| 38 | 26 | Network out of order | | The destination cannot be reached because the network is not functioning correctly, and the condition might last for an extended period of time. An immediate reconnect attempt will probably be unsuccessful . |
| 41 | 29 | Temporary failure | | An error occurred because the network is not functioning correctly. The problem will be resolved shortly. |
| 42 | 2A | Switching equipment congestion | | The destination cannot be reached because the network-switching equipment is temporarily overloaded. |
| 43 | 2B | Access information discarded | Discarded information element identifier(s) (Note 5) | The network cannot provide the requested access information. |
| 44 | 2C | Requested circuit/channel not available | | The remote equipment cannot provide the requested channel for an unknown reason. This might be a temporary problem. |
| 47 | 2F | Resources unavailable, unspecified | | The requested channel or service is unavailable for an unknown reason. This might be a temporary problem. |
| 49 | 31 | Quality of service unavailable | Table A-2 | The requested quality of service cannot be provided by the network. This might be a subscription problem. |
| 50 | 32 | Requested facility not subscribed | Facility identification (Note 1) | The remote equipment supports the requested supplementary service by subscription only. |
| 57 | 39 | Bearer capability not authorized | Note 3 | The user requested a bearer capability that the network provides, but the user is not authorized to use it. This might be a subscription problem. |
| 58 | 3A | Bearer capability not presently available | Note 3 | The network normally provides the requested bearer capability, but it is unavailable at the present time. This might be the result of a temporary network problem or to a subscription problem. |
| 63 | 3F | Service or option not available, unspecified | | The network or remote equipment was incapable of providing the requested service option for an unspecified reason. This might be a subscription problem. |
| 65 | 41 | Bearer capability not implemented | Note 3 | The network cannot provide the bearer capability requested by the user. |
| 66 | 42 | Channel type not implemented | Channel Type (Note 6) | The network or the destination equipment does not support the requested channel type. |
| 69 | 45 | Requested facility not implemented | Facility Identification (Note 1) | The remote equipment does not support the requested supplementary service. |
| 70 | 46 | Only restricted digital information bearer capability is available | | The network is incapable of providing unrestricted digital information bearer capability. |
| 79 | 4F | Service or option not implemented, unspecified | | The network or remote equipment is incapable of providing the requested service option for an unspecified reason. This might be a subscription problem. |
| 81 | 51 | Invalid call reference value | | The remote equipment received a call with a call reference that is not currently in use on the user-network interface. |
| 82 | 52 | Identified channel does not exist | Channel identity | The receiving equipment is requested to use a channel that is not activated on the interface for calls. |
| 83 | 53 | A suspended call exists, but this call identity does not | | The network received a call resume request. The call resume request contained a call identify information element that indicates that the call identity is being used for a suspended call. |
| 84 | 54 | Call identity in use | | The network received a call resume request. The call resume request contained a Call Identify information element that indicates that it is in use for a suspended call. |
| 85 | 55 | No call suspended | | The network received a call resume request when there was not a suspended call pending. This might be a transient error that will be resolved by successive call retries. |
| 86 | 56 | Call having the requested call identity has been cleared | Clearing cause | The network received a call resume request. The call resume request contained a call identity information element, which once indicated a suspended call. However, the suspended call was cleared either by timeout or by the remote user. |
| 88 | 58 | Incompatible destination | Incompatible parameter (Note 2) | This indicates that an attempt was made to connect to non-ISDN equipment ”for example, to an analog line. |
| 91 | 5B | Invalid transit network selection | | The ISDN exchange was asked to route the call through an unrecognized intermediate network. |
| 95 | 5F | Invalid message, unspecified | | An invalid message was received, and no standard cause applies. This is usually the result of a D-channel error. If this error occurs systematically, report it to your ISDN service provider. |
| 96 | 60 | Mandatory information element is missing | Information element identifier(s) (Note 5) | The receiving equipment received a message that did not include one of the mandatory information elements. This is usually the result of a D-channel error. If this error occurs systematically, reportit to your ISDN service provider. |
| 97 | 61 | Message type nonexistent or not implemented | Message type | The receiving equipment received an unrecognized message, either because the message type was invalid or because the message type was valid but not supported. The cause is either a problem with the remote configuration or a problem with the local D channel. |
| 98 | 62 | Message not compatible with call state or message type nonexistent or not implemented | Message type | The remote equipment received an invalid message, and no standard cause applies. This cause is a D-channel error. If this error occurs systematically, report it to your ISDN service provider. |
| 99 | 63 | Information element nonexistent or not implemented | Information element identifier(s) (Notes 5 and 7) | The remote equipment received a message that includes information elements that were not recognized. This is usually the result of a D-channel error. If this error occurs systematically, report it to your ISDN service provider. |
| 100 | 64 | Invalid information element contents | Information element identifier(s) (Note 5) | The remote equipment received a message that includes invalid information in the information element. This is usually the result of a D-channel error. |
| 101 | 65 | Message not compatible with call state | Message type | The remote equipment received an unexpected message that does not correspond to the current state of the connection. This is usually the result of a D-channel error. |
| 102 | 66 | Recovery on timer expires | Timer number (Note 8) | An error-handling (recovery) procedure was initiated by a timer expiry. This is usually a temporary problem. |
| 111 | 6F | Protocol error, unspecified | | This is the result of an unspecified D-channel error when no other standard cause applies. |
| 127 | 7F | Internetworking, unspecified | | An event occurred, but the network does not provide causes for the action that it takes. The precise problem is unknown. |
