The messages I-ClrRx and I-ClrTx found in the event log show a "cause" field which corresponds to what has been specified by the ITU in Recommendations Q.931 e Q.850.
The complete format, which includes some optional values, is described in Table 1. Full format for ITU "cause" element. The most frequent format is reported in Table 2. Most frequent format for the ITU "cause" element.
For a complete description of all the options, refer to recommendation ITU Q.850.
Recommendation Q.931 enumerates the bytes starting from the 3rd, because the entire information element relating to "cause" contains two other bytes at the beginning, which specify the element itself, "cause", and the total length.
Since these values do not influence the content of the "cause" field and vice versa, they are not registered and are not taken into consideration for the interpretation which follows.
| Bit # | Byte #, (NOTE 3) | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | Q.931 | Q.763 |
| 0/1 ext. |
Coding standard | 0 Spare |
Location | 3 | 1 | ||||
| 1 ext. |
Recommendation (NOTE 1) (NOTE 2) | 3a* | |||||||
| 1 ext. |
Cause value | 4 | 2 | ||||||
| Diagnostic(s) (if any) | 5* | 3* | |||||||
NOTES
If the default applies for the Recommendation field, the byte including this field shall be omitted. The Recommendation field is not supported by the ISUP. The default interpretation for ISUP is Q.763. Optional bytes are marked with asterisks (*).
In EURO-Isdn networks, and in particular in basic rate accesses (BRI), byte 3a (Recommendation), is absent, while the diagnostic field is only present for certain disconnectioins.
To simplify, the format for the ISDN disconnection "cause" element most frequently encountered, is the one shown in the table following.
| Bit # | Byte # | |||||||
|---|---|---|---|---|---|---|---|---|
| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | Q.931 |
| 1 | Coding standard | 0 Spare |
Location | 3 | ||||
| 1 | Cause value | 4 | ||||||
| Diagnostic(s) (if any) | 5* | |||||||
| Bits | 7 | 6 | |
|---|---|---|---|
| 0 | 0 | CCITT standardized coding, as described below | |
| 0 | 1 | ISO/IEC standard (see NOTE) | |
| 1 | 0 | National standard (see NOTE) | |
| 1 | 1 | Standard specific to identified location (see NOTE) |
NOTE - These other coding standards should be used only when the desired cause value cannot be represented with the CCITT-standardized coding.
| Bits | 4 | 3 | 2 | 1 | Location | Brief description |
|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | user (U) | Originated by user equipment, i.e phone. | |
| 0 | 0 | 0 | 1 | private network serving the local user (LPN) | Generated by a private networking device, e.g. a PABX, on the side which is directly connected to the receiving device. | |
| 0 | 0 | 1 | 0 | public network serving the local user (LN) | Generated by the public network, e.g. a Telco, on the side which is directly connected to the receiving device. | |
| 0 | 0 | 1 | 1 | transit network (TN) | Generated somewhere in an intermediate network on which the call is transiting. | |
| 0 | 1 | 0 | 0 | public network serving the remote user (RLN) | Generated by the public network, e.g. a Telco, on the remote side respect to the receiving device. | |
| 0 | 1 | 0 | 1 | private network serving the remote user (RPN) | Generated by a private networking device, e.g. a PABX, on the remote side respect to the receiving device. | |
| 0 | 1 | 1 | 1 | international network (INTL) | Generated somewhere in the international network. | |
| 1 | 0 | 1 | 0 | network beyond interworking point (BI) | Generated by a non-ISDN network interconnected to the ISDN network. | |
| All other values are reserved. | ||||||
NOTE - The actual meaning of locations is deeply explained in ITU recommendations, however the table above introduces a brief description.
The "cause" values are subdivided in two parts: class and value.
The names of the classes are listed following, however, each "cause" is uniquely identifiable even without looking up the classes.
| Bits | 7 | 6 | 5 | Location |
|---|---|---|---|---|
| 0 | 0 | 0 | normal event | |
| 0 | 0 | 1 | normal event | |
| 0 | 1 | 0 | resource unavailable | |
| 0 | 1 | 1 | service or option not available | |
| 1 | 0 | 0 | service or option not implemented | |
| 1 | 0 | 1 | invalid message (e.g. parameter out of range) | |
| 1 | 1 | 0 | protocol error (e.g. unknown message | |
| 1 | 1 | 1 | Interworking |
| Cause value | ITU definition as per Q.850 recommendation. | |||
|---|---|---|---|---|
| Class | Value | No.(dec) | No.(*) (hex) | |
| 000 | 0001 | 1 | 01 (81) | Unallocated (unassigned) number. This cause indicates that the called party cannot be reached because, although the called party number is in a valid format, it is not currently allocated (assigned). |
| 000 | 0010 | 2 | 02 (82) | No route to specified transit network (national use). This cause indicates that the equipment sending this cause has received a request to route the call through a particular transit network which it does not recognize. The equipment sending this cause does not recognize the transit network either because the transit network does not exist or because that particular transit network, while it does exist, does not serve the equipment which is sending this cause. This cause is supported on a network-dependent basis. |
| 000 | 0011 | 3 | 03 (83) | No route to destination. This cause indicates that the called party cannot be reached because the network through which the call has been routed does not serve the destination desired. This cause is supported on a network-dependent basis. |
| 000 | 0100 | 4 | 04 (84) | Send special information tone. This 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. |
| 000 | 0101 | 5 | 05 (85) | Misdialled trunk prefix (national use). This cause indicates the erroneous inclusion of a trunk prefix in the number of the called party. |
| 000 | 0110 | 6 | 06 (86) | Channel unacceptable. This cause indicates that the channel most recently identified is not acceptable to the sending entity for use in this call. |
| 000 | 0111 | 7 | 07 (87) | Call awarded and being delivered in an established
channel. This 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 X.25 virtual calls). |
| 000 | 1000 | 8 | 08 (88) | Preemption. This cause indicates that the call is being preempted. |
| 000 | 1001 | 9 | 09 (89) | Preemption - circuit reserved for reuse. This cause indicates that the call is being preempted and the circuit is reserved for reuse by the preempting exchange. |
| 001 | 0000 | 16 | 10 (90) | Normal call clearing. This cause indicates that the call is being cleared because one of the users involved in the call has requested that the call be cleared. Under normal situations, the source of this cause is not the network. |
| 001 | 0001 | 17 | 11 (91) | User busy. This cause is used to indicate that the called party is unable to accept another call because the user busy condition has been encountered. This cause value may be generated by the called user or by the network. In the case of user determine user busy, it is noted that the user equipment is compatible with the call. |
| 001 | 0010 | 18 | 12 (92) | No user responding. This cause is used when a called party does not respond to a call establishment message with either an alerting or connect indication within the prescribed period of time allocated. |
| 001 | 0011 | 19 | 13 (93) | No answer from user (user
alerted). This cause is used when the called party has been alerted but does not respond with a connect indication within a prescribed period of time. NOTE - This cause is not necessarily generated by Q.931 procedures but may be generated by internal network timers. |
| 001 | 0100 | 20 | 14 (94) | Subscriber absent. This cause value is used when a mobile station has logged off, radio contact is not obtained with a mobile station or if a personal telecommunication user is temporarily not addressable at any user-network interface. |
| 001 | 0101 | 21 | 15 (95) | Call rejected. This cause indicates that the equipment sending this cause does not wish to accept this call, although it could have accepted the call because the equipment sending this cause is neither busy nor incompatible. This cause may also be generated by the network, indicating that the call was cleared due to a supplementary service constraint. The diagnostic field may contain additional information about the supplementary service and reason for rejection. |
| 001 | 0110 | 22 | 16 (96) | Number changed. This cause is returned to a calling party when the called party number indicated by the calling party is no longer assigned. The new called party number may optionally be included in the diagnostic field. If a network does not support this cause value, cause No. 1, unallocated (unassigned) number shall be used. |
| 001 | 1010 | 26 | 1A (9A) | Non-selected user clearing. This cause indicates that the user has not been awarded the incoming call. |
| 001 | 1011 | 27 | 1B (9B) | Destination out of order. This cause indicates that the destination indicated by the user cannot be reached because the interface to the destination is not functioning correctly. The term "not functioning correctly" indicates that a signalling message was unable to be delivered to the remote party; e.g. a physical layer or data link layer failure at the remote party, or user equipment off-line. |
| 001 | 1100 | 28 | 1C (9C) | Invalid number format (address
incomplete). This cause indicates that the called party cannot be reached because the called party number is not in a valid format or is not complete. NOTE - This condition may be determined immediately after reception of an ST signal or on time-out after the last received digit. |
| 001 | 1101 | 29 | 1D (9D) | Facility rejected. This cause is returned when a supplementary service requested by the user cannot be provided by the network. |
| 001 | 1110 | 30 | 1E (9E) | Response to STATUS ENQUIRY. This cause is included in the STATUS message when the reason for generating the STATUS message was the prior receipt of a STATUS ENQUIRY message. |
| 001 | 1111 | 31 | 1F (9F) | Normal, unspecified. This cause is used to report a normal event only when no other cause in the normal class applies. |
| 010 | 0010 | 34 | 22 (A2) | No circuit/channel
available. This cause indicates that there is no appropriate circuit/channel presently available to handle the call. |
| 010 | 0110 | 38 | 26 (A6) | Network out of order. This cause indicates that the network is not functioning correctly and that the condition is likely to last a relatively long period of time; i.e. immediately re-attempting the call is not likely to be successful. |
| 010 | 0111 | 39 | 27 (A7) | Permanent frame mode connection
out-of-service. This 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/Q.933). |
| 010 | 1000 | 40 | 28 (A8) | Permanent frame mode connection
operational. This 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/Q.933). |
| 010 | 1001 | 41 | 29 (A9) | Temporary failure. This cause indicates that the network is not functioning correctly and that the condition is not likely to last a long period of time; i.e. the user may wish to try another call attempt almost immediately. |
| 010 | 1010 | 42 | 2A (AA) | Switching equipment
congestion. This cause indicates that the switching equipment generating this cause is experiencing a period of high traffic. |
| 010 | 1011 | 43 | 2B (AB) | Access information
discarded. This 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. |
| 010 | 1100 | 44 | 2C (AC) | Requested circuit/channel not
available. This cause is returned when the circuit or channel indicated by the requesting entity cannot be provided by the other side of the interface. |
| 010 | 1110 | 46 | 2E (AE) | Precedence call blocked. This cause indicates that there are no preemptable circuits or that the called user is busy with a call of equal or higher preemptable level. |
| 010 | 1111 | 47 | 2F (AF) | Resource unavailable,
unspecified. This cause is used to report a resource unavailable event only when no other cause in the resource unavailable class applies. |
| 011 | 0001 | 49 | 31 (B1) | Quality of Service not
available. This cause is used to report that the requested Quality of Service, as defined in Recommendation X.213, cannot be provided (e.g. throughput or transit delay cannot be supported). |
| 011 | 0010 | 50 | 32 (B2) | Requested facility not
subscribed. This cause indicates that the user has requested a supplementary service which is implemented by the equipment which generated this cause, but which the user is not authorized to use. |
| 011 | 0101 | 53 | 35 (B5) | Outgoing calls barred within
CUG. This 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. |
| 011 | 0111 | 55 | 37 (B7) | Incoming calls barred within
CUG. This cause indicates that although the called party is a member of the CUG for the incoming CUG call, incoming calls are not allowed to this member of the CUG. |
| 011 | 1001 | 57 | 39 (B9) | Bearer capability not
authorized. This cause indicates that the user has requested a bearer capability which is implemented by the equipment which generated this cause but which the user is not authorized to use. |
| 011 | 1010 | 58 | 3A (BA) | Bearer capability not presently
available. This cause indicates that the user has requested a bearer capability which is implemented by the equipment which generated this cause but which is not available at this time. |
| 011 | 1110 | 62 | 3E (BE) | Inconsistency in designated outgoing
access information and subscriber class. This cause indicates that there is an inconsistency in the designated outgoing access information and subscriber class. |
| 011 | 1111 | 63 | 3F (BF) | Service or option not available,
unspecified. This cause is used to report a service or option not available event only when no other cause in the service or option not available class applies. |
| 100 | 0001 | 65 | 41 (C1) | Bearer capability not
implemented. This cause indicates that the equipment sending this cause does not support the bearer capability requested. |
| 100 | 0010 | 66 | 42 (C2) | Channel type not
implemented. This cause indicates that the equipment sending this cause does not support the channel type requested. |
| 100 | 0101 | 69 | 45 (C5) | Requested facility not
implemented. This cause indicates that the equipment sending this cause does not support the requested supplementary service. |
| 100 | 0110 | 70 | 46 (C6) | Only restricted digital information
bearer capability is available (national use). This cause indicates that the calling party has requested an unrestricted bearer service but that the equipment sending this cause only supports the restricted version of the requested bearer capability. |
| 100 | 1111 | 79 | 4F (CF) | Service or option not implemented,
unspecified. This cause is used to report a service or option not implemented event only when no other cause in the service or option not implemented class applies. |
| 101 | 0001 | 81 | 51 (D1) | Invalid call reference
value. This 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. |
| 101 | 0010 | 82 | 52 (D2) | Identified channel does not
exist. This 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 through 23, this cause is generated. |
| 101 | 0011 | 83 | 53 (D3) | A suspended call exists, but this call
identity does not. This 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). |
| 101 | 0100 | 84 | 54 (D4) | Call identity in use. This 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. |
| 101 | 0101 | 85 | 55 (D5) | No call suspended. This 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. |
| 101 | 0110 | 86 | 56 (D6) | Call having the requested call identity
has been cleared. This 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). |
| 101 | 0111 | 87 | 57 (D7) | User not member of CUG. This cause indicates that the called user for the incoming CUG call is not a member of the specified CUG or that the calling user is an ordinary subscriber calling a CUG subscriber. |
| 101 | 1000 | 88 | 58 (D8) | Incompatible destination. This cause indicates that the equipment sending this cause has received a request to establish a call which has low layer compatibility, high layer compatibility, or other compatibility attributes (e.g. data rate) which cannot be accommodated. |
| 101 | 1010 | 90 | 5A (DA) | Non-existent CUG. This cause indicates that the specified CUG does not exist. |
| 101 | 1011 | 91 | 5B (DB) | Invalid 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/Q.931. |
| 101 | 1111 | 95 | 5F (DF) | Invalid message,
unspecified. This cause is used to report an invalid message event only when no other cause in the invalid message class applies. |
| 110 | 0000 | 96 | 60 (E0) | Mandatory information element is
missing. This 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. |
| 110 | 0001 | 97 | 61 (E1) | Message type non-existent or not
implemented. This cause indicates that the equipment sending this cause has received a message with a message type which it does not recognize either because this is a message not defined or is defined but not implemented by the equipment sending this cause. |
| 110 | 0010 | 98 | 62 (E2) | Message not compatible with call state or
message type non-existent or not implemented. This cause indicates that the equipment sending this cause has received a message such 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. |
| 110 | 0011 | 99 | 63 (E3) | Information element/parameter
non-existent or not implemented. This 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) are not defined or are defined but not implemented by the equipment sending the cause. This cause indicates that the information element(s)/parameter(s) were 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. |
| 110 | 0100 | 100 | 64 (E4) | Invalid information element
contents. This 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. |
| 110 | 0101 | 101 | 65 (E5) | Message not compatible with call
state. This cause indicates that a message has been received which is incompatible with the call state. |
| 110 | 0110 | 102 | 66 (E6) | Recovery on timer expiry. This cause indicates that a procedure has been initiated by the expiry of a timer in association with error-handling procedures. |
| 110 | 0111 | 103 | 67 (E7) | Parameter non-existent or not implemented
- passed on (national use). 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) were ignored. In addition, if the equipment sending this cause is an intermediate point, then this cause indicates that the parameter(s) were passed on unchanged. |
| 110 | 1110 | 110 | 6E (EE) | Message with unrecognized parameter
discarded. This cause indicates that the equipment sending this cause has discarded a received message which includes a parameter that is not recognized. |
| 110 | 1111 | 111 | 6F (EF) | Protocol error, unspecified. This cause is used to report a protocol error event only when no other cause in the protocol error class applies. |
| 111 | 1111 | 127 | 7F (FF) | Interworking, unspecified. This cause indicates that there has been interworking with a network which does not provide causes for actions it takes. Thus, the precise cause for a message which is being sent cannot be ascertained. |
(*) The hexadecimal value in brackets is the value which also includes the most significant bit with the value "1", that normally present, with the purpose is to simplify decoding.
For example, the code "I-ClrRx cause:80 92" is defined as: "CCITT coding", "User location", "Normal event", "No user responding".
In "I-ClrRx" and "I-ClrTx" messages it is sometimes possibile for codes to be reported which are not codified by ITU, or are codified as "specific for the specified location: user".
These are specific codes used by CPX to indicate particular events.
Codes starting with FF as the first byte, report local problems, i.e. they are not messages sent or received by the network.
Codes starting with 80 as the first byte, are codes specific to CPX, sent or received by the network. It should be noted that these "private" codes might not be transported to their destination by ISDN, exactly as happens with the Italian Telecom network.
| Cause | Description |
|---|---|
| FF A0 | The calling number ("CGO" in the MLM driver) specified in the call cannot be associated with any ISDN line ("NUM" in the Q931 driver). |
| FF A3 | The "cause" field is absent. |
| FF A5 | Level 1 of ISDN is inactive. |
| FF A6 | Level 2 of ISDN in inactive, or failed to activate. |
| FF B3 | No "B" channels were available. |
| 80 80 | Closure caused by SHM feature of the MLM driver. |
| 80 8A | Closure caused by "INIT" command issued to the MLM driver. |
| 80 8B | Closure caused by an error discovered by the MPX protocol in the MLM driver, usually a failure in link-check frame exchange. |
| 80 8C | Closure caused by the restoration of READY state in the P-LINK& interface of the MLM diriver. |
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