Showing 0 of 0 cause codes
Q.850 to SIP Response Code Mapping (RFC 3398)
| Q.850 Cause | Description | SIP Code | SIP Description |
|---|---|---|---|
| 1 | Unallocated number | 404 | Not Found |
| 2 | No route to network | 404 | Not Found |
| 3 | No route to destination | 404 | Not Found |
| 16 | Normal call clearing | BYE | Normal hangup |
| 17 | User busy | 486 | Busy Here |
| 18 | No user responding | 408 | Request Timeout |
| 19 | No answer from user | 480 | Temporarily Unavailable |
| 20 | Subscriber absent | 480 | Temporarily Unavailable |
| 21 | Call rejected | 403 | Forbidden |
| 22 | Number changed | 410 | Gone |
| 27 | Destination out of order | 502 | Bad Gateway |
| 28 | Invalid number format | 484 | Address Incomplete |
| 29 | Facility rejected | 501 | Not Implemented |
| 31 | Normal, unspecified | 480 | Temporarily Unavailable |
| 34 | No circuit/channel available | 503 | Service Unavailable |
| 38 | Network out of order | 503 | Service Unavailable |
| 41 | Temporary failure | 503 | Service Unavailable |
| 42 | Switching equipment congestion | 503 | Service Unavailable |
| 47 | Resource unavailable | 503 | Service Unavailable |
| 55 | Incoming calls barred | 403 | Forbidden |
| 57 | Bearer capability not authorized | 403 | Forbidden |
| 58 | Bearer capability not available | 503 | Service Unavailable |
| 63 | Service/option not available | 503 | Service Unavailable |
| 65 | Bearer capability not implemented | 488 | Not Acceptable Here |
| 79 | Service not implemented | 501 | Not Implemented |
| 88 | Incompatible destination | 488 | Not Acceptable Here |
| 102 | Recovery on timer expiry | 504 | Server Timeout |
| 111 | Protocol error | 500 | Server Internal Error |
| 127 | Interworking, unspecified | 500 | Server Internal Error |
What are Q.850 Cause Codes?
ITU-T Recommendation Q.850 defines cause codes used in ISDN, PRI (T1/E1), and VoIP networks to indicate why a call was disconnected or failed. These codes are carried in the ISDN DISCONNECT, RELEASE, and RELEASE COMPLETE messages, and in SIP via the Reason header (e.g., Reason: Q.850;cause=16). They are essential for troubleshooting call failures in telecom networks.
Where Q.850 Codes Appear
- ISDN/PRI: In Q.931 DISCONNECT, RELEASE messages
- SIP: In the
Reasonheader of BYE/CANCEL - CDR Records: As disconnect cause in billing systems
- VoIP Gateways: Cisco, Audiocodes, Ribbon, etc.
- Softswitch Logs: FreeSWITCH, Asterisk, Oraclecom
Troubleshooting Tips
- Cause 1-3: Check number format, routing tables, and number porting
- Cause 16: Normal - both parties hung up properly
- Cause 17-21: User-side issues - busy, no answer, call rejected
- Cause 34, 38, 41-42: Network capacity issues - check trunk utilization
- Cause 127: Catch-all - check gateway logs for real cause
Related Resources
SIP Response Codes - Complete SIP status code reference
SIP Call Flow - Visual SIP message diagrams
Telecom Abbreviations - ISDN, PRI, Q.931, and more