Reference
Q.850 causes (hangup cause): the full list and SIP map
The Q.850 cause is the number the telephone network gives for the end of a call: 16 when it ends normally, 17 when the number is busy, 34 when no channel is free. It travels in the release message on E1 trunks and, on SIP trunks, in the Reason: Q.850;cause=N header.
Where does the Q.850 cause show up?
On E1 trunks (SS7/ISUP or ISDN), the cause comes in the call's release message. On SIP trunks, the carrier or the SBC repeats it in the Reason header of the response (RFC 6432). In Asterisk, Issabel and FreePBX it is theHANGUPCAUSE variable and the CDR's hangupcause field.
The 72 ITU-T Q.850 causes
| Cause | Official name | Class |
|---|---|---|
| Cause 1 | Unallocated (unassigned) number | Normal event (1 to 31) |
| Cause 2 | No route to specified transit network (national use) | Normal event (1 to 31) |
| Cause 3 | No route to destination | Normal event (1 to 31) |
| Cause 4 | Send special information tone | Normal event (1 to 31) |
| Cause 5 | Misdialled trunk prefix (national use) | Normal event (1 to 31) |
| Cause 6 | Channel unacceptable | Normal event (1 to 31) |
| Cause 7 | Call awarded and being delivered in an established channel | Normal event (1 to 31) |
| Cause 8 | Pre-emption | Normal event (1 to 31) |
| Cause 9 | Pre-emption – circuit reserved for reuse | Normal event (1 to 31) |
| Cause 13 | Call completed elsewhere | Normal event (1 to 31) |
| Cause 14 | QoR: ported number | Normal event (1 to 31) |
| Cause 16 | Normal call clearing | Normal event (1 to 31) |
| Cause 17 | User busy | Normal event (1 to 31) |
| Cause 18 | No user responding | Normal event (1 to 31) |
| Cause 19 | No answer from user (user alerted) | Normal event (1 to 31) |
| Cause 20 | Subscriber absent | Normal event (1 to 31) |
| Cause 21 | Call rejected | Normal event (1 to 31) |
| Cause 22 | Number changed | Normal event (1 to 31) |
| Cause 23 | Redirection to new destination | Normal event (1 to 31) |
| Cause 24 | Call rejected due to feature at the destination | Normal event (1 to 31) |
| Cause 25 | Exchange – routing error | Normal event (1 to 31) |
| Cause 26 | Non-selected user clearing | Normal event (1 to 31) |
| Cause 27 | Destination out of order | Normal event (1 to 31) |
| Cause 28 | Invalid number format (address incomplete) | Normal event (1 to 31) |
| Cause 29 | Facility rejected | Normal event (1 to 31) |
| Cause 30 | Response to STATUS ENQUIRY | Normal event (1 to 31) |
| Cause 31 | Normal, unspecified | Normal event (1 to 31) |
| Cause 34 | No circuit/channel available | Resource unavailable (34 to 47) |
| Cause 38 | Network out of order | Resource unavailable (34 to 47) |
| Cause 39 | Permanent frame mode connection out of service | Resource unavailable (34 to 47) |
| Cause 40 | Permanent frame mode connection operational | Resource unavailable (34 to 47) |
| Cause 41 | Temporary failure | Resource unavailable (34 to 47) |
| Cause 42 | Switching equipment congestion | Resource unavailable (34 to 47) |
| Cause 43 | Access information discarded | Resource unavailable (34 to 47) |
| Cause 44 | Requested circuit/channel not available | Resource unavailable (34 to 47) |
| Cause 46 | Precedence call blocked | Resource unavailable (34 to 47) |
| Cause 47 | Resource unavailable, unspecified | Resource unavailable (34 to 47) |
| Cause 49 | Quality of service not available | Service or option not available (49 to 63) |
| Cause 50 | Requested facility not subscribed | Service or option not available (49 to 63) |
| Cause 53 | Outgoing calls barred within CUG | Service or option not available (49 to 63) |
| Cause 55 | Incoming calls barred within CUG | Service or option not available (49 to 63) |
| Cause 57 | Bearer capability not authorized | Service or option not available (49 to 63) |
| Cause 58 | Bearer capability not presently available | Service or option not available (49 to 63) |
| Cause 62 | Inconsistency in designated outgoing access information and subscriber class | Service or option not available (49 to 63) |
| Cause 63 | Service or option not available, unspecified | Service or option not available (49 to 63) |
| Cause 65 | Bearer capability not implemented | Service or option not implemented (65 to 79) |
| Cause 66 | Channel type not implemented | Service or option not implemented (65 to 79) |
| Cause 69 | Requested facility not implemented | Service or option not implemented (65 to 79) |
| Cause 70 | Only restricted digital information bearer capability is available (national use) | Service or option not implemented (65 to 79) |
| Cause 79 | Service or option not implemented, unspecified | Service or option not implemented (65 to 79) |
| Cause 81 | Invalid call reference value | Invalid message (81 to 95) |
| Cause 82 | Identified channel does not exist | Invalid message (81 to 95) |
| Cause 83 | A suspended call exists, but this call identity does not | Invalid message (81 to 95) |
| Cause 84 | Call identity in use | Invalid message (81 to 95) |
| Cause 85 | No call suspended | Invalid message (81 to 95) |
| Cause 86 | Call with the requested call identity has been cleared | Invalid message (81 to 95) |
| Cause 87 | User not member of CUG | Invalid message (81 to 95) |
| Cause 88 | Incompatible destination | Invalid message (81 to 95) |
| Cause 90 | Non-existent CUG | Invalid message (81 to 95) |
| Cause 91 | Invalid transit network selection (national use) | Invalid message (81 to 95) |
| Cause 95 | Invalid message, unspecified | Invalid message (81 to 95) |
| Cause 96 | Mandatory information element is missing | Protocol error (96 to 111) |
| Cause 97 | Message type non-existent or not implemented | Protocol error (96 to 111) |
| Cause 98 | Message not compatible with call state or message type non-existent or not implemented | Protocol error (96 to 111) |
| Cause 99 | Information element/parameter non-existent or not implemented | Protocol error (96 to 111) |
| Cause 100 | Invalid information element contents | Protocol error (96 to 111) |
| Cause 101 | Message not compatible with call state | Protocol error (96 to 111) |
| Cause 102 | Recovery on timer expiry | Protocol error (96 to 111) |
| Cause 103 | Parameter non-existent or not implemented – passed on (national use) | Protocol error (96 to 111) |
| Cause 110 | Message with unrecognized parameter discarded | Protocol error (96 to 111) |
| Cause 111 | Protocol error, unspecified | Protocol error (96 to 111) |
| Cause 127 | Interworking, unspecified | Interworking (127) |
From Q.850 cause to SIP code (RFC 3398, §7.2.4.1)
| Q.850 cause | SIP response | Note |
|---|---|---|
| 1 (unallocated number) | SIP 404 Not Found | |
| 2 (no route to network) | SIP 404 Not Found | |
| 3 (no route to destination) | SIP 404 Not Found | |
| 16 (normal call clearing) | None | (*) usually results in a BYE or CANCEL, no status code |
| 17 (user busy) | SIP 486 Busy Here | |
| 18 (no user responding) | SIP 408 Request Timeout | |
| 19 (no answer from the user) | SIP 480 Temporarily Unavailable | |
| 20 (subscriber absent) | SIP 480 Temporarily Unavailable | |
| 21 (call rejected) | SIP 403 Forbidden | (+) if cause location is user, 603 could be given instead |
| 22 (number changed (w/o diagnostic)) | SIP 410 Gone | |
| 22 (number changed (w/ diagnostic)) | 301 Moved Permanently | new number from diagnostic SHOULD go in Contact |
| 23 (redirection to new destination) | SIP 410 Gone | |
| 26 (non-selected user clearing) | SIP 404 Not Found | (=) ANSI: misrouted ported number |
| 27 (destination out of order) | SIP 502 Bad Gateway | |
| 28 (address incomplete) | SIP 484 Address Incomplete | |
| 29 (facility rejected) | SIP 501 Not Implemented | |
| 31 (normal unspecified) | SIP 480 Temporarily Unavailable | |
| 34 (no circuit available) | SIP 503 Service Unavailable | |
| 38 (network out of order) | SIP 503 Service Unavailable | |
| 41 (temporary failure) | SIP 503 Service Unavailable | |
| 42 (switching equipment congestion) | SIP 503 Service Unavailable | |
| 47 (resource unavailable) | SIP 503 Service Unavailable | |
| 55 (incoming calls barred within CUG) | SIP 403 Forbidden | |
| 57 (bearer capability not authorized) | SIP 403 Forbidden | |
| 58 (bearer capability not presently available) | SIP 503 Service Unavailable | |
| 65 (bearer capability not implemented) | SIP 488 Not Acceptable Here | |
| 70 (only restricted digital avail) | SIP 488 Not Acceptable Here | |
| 79 (service or option not implemented) | SIP 501 Not Implemented | |
| 87 (user not member of CUG) | SIP 403 Forbidden | |
| 88 (incompatible destination) | SIP 503 Service Unavailable | |
| 102 (recovery of timer expiry) | SIP 504 Server Time-out | |
| 111 (protocol error) | SIP 500 Server Internal Error | |
| 127 (interworking unspecified) | SIP 500 Server Internal Error | |
| Any other ((not listed)) | SIP 500 Server Internal Error | default for unlisted causes (SHOULD) |
| 44 (requested circuit or channel not available) | None | untranslatable: should not result in any SIP status; originating switch retries another CIC |
From SIP code to Q.850 cause (RFC 3398, §8.2.6.1)
| SIP response | Q.850 cause | Note |
|---|---|---|
| SIP 400 Bad Request | 41 (Temporary Failure) | |
| SIP 401 Unauthorized | 21 (Call rejected) | (*) try to authenticate first |
| SIP 402 Payment required | 21 (Call rejected) | |
| SIP 403 Forbidden | 21 (Call rejected) | |
| SIP 404 Not found | 1 (Unallocated number) | |
| SIP 405 Method not allowed | 63 (Service or option unavailable) | |
| SIP 406 Not acceptable | 79 (Service/option not implemented) | (+) |
| SIP 407 Proxy authentication required | 21 (Call rejected) | (*) try to authenticate first |
| SIP 408 Request timeout | 102 (Recovery on timer expiry) | |
| SIP 410 Gone | 22 (Number changed (w/o diagnostic)) | |
| SIP 413 Request Entity too long | 127 (Interworking) | (+) |
| SIP 414 Request-URI too long | 127 (Interworking) | (+) |
| SIP 415 Unsupported media type | 79 (Service/option not implemented) | (+) |
| SIP 416 Unsupported URI Scheme | 127 (Interworking) | (+) |
| SIP 420 Bad extension | 127 (Interworking) | (+) |
| SIP 421 Extension Required | 127 (Interworking) | (+) |
| SIP 423 Interval Too Brief | 127 (Interworking) | (+) |
| SIP 480 Temporarily unavailable | 18 (No user responding) | |
| SIP 481 Call/Transaction Does not Exist | 41 (Temporary Failure) | |
| SIP 482 Loop Detected | 25 (Exchange - routing error) | |
| SIP 483 Too many hops | 25 (Exchange - routing error) | |
| SIP 484 Address incomplete | 28 (Invalid Number Format) | (+) |
| SIP 485 Ambiguous | 1 (Unallocated number) | |
| SIP 486 Busy here | 17 (User busy) | |
| SIP 487 Request Terminated | From the Warning header | |
| SIP 488 Not Acceptable here | From the Warning header | default 31; 65 if Warning is about bearer capability |
| SIP 500 Server internal error | 41 (Temporary failure) | |
| SIP 501 Not implemented | 79 (Not implemented, unspecified) | |
| SIP 502 Bad gateway | 38 (Network out of order) | |
| SIP 503 Service unavailable | 41 (Temporary failure) | |
| SIP 504 Server time-out | 102 (Recovery on timer expiry) | |
| SIP 505 Version Not Supported | 127 (Interworking) | (+) RFC text prints 504; corrected to 505 by Errata ID 2161 (Held for Document Update) |
| SIP 513 Message Too Large | 127 (Interworking) | (+) |
| SIP 600 Busy everywhere | 17 (User busy) | |
| SIP 603 Decline | 21 (Call rejected) | |
| SIP 604 Does not exist anywhere | 1 (Unallocated number) | |
| SIP 606 Not acceptable | From the Warning header | default 31; 65 if Warning is about bearer capability |
| Any other (not listed) | 31 (Normal, unspecified) | default for unlisted status codes |
Sources: ITU-T Q.850 (10/18, with amendment 1 of 04/19), RFC 3398 (with its errata) and RFC 6432, checked on October 7, 2026.
Every failure with its cause, ready for the carrier
Monitor keeps the SIP code and the Q.850 cause of every test call and delivers them in the incident's evidence.