Call Hangup Cause Codes (Q.850 Standard)

In telecommunication systems—whether ISDN, VoIP, or other networks—understanding why a call ended is critical for troubleshooting, billing, analytics, and improving call quality. The Q.850 Cause Codes provide a standardized way to indicate the precise reason for a call disconnection or hangup.

What Are Q.850 Cause Codes?

The Q.850 Cause Codes are a set of standardized numeric values defined by the International Telecommunication Union (ITU) under the ITU-T Recommendation Q.850. They provide a consistent way for telecommunication systems, including ISDN and VoIP, to indicate why a call was disconnected or terminated.

In our system, the "hangup Cause" field uses these codes descriptions to give you detailed information on the cause of call disconnection in your webhook and Call Detail Records (CDR).

The keys listed below can be used to obtain these values from the webhook payload. These parameters are included only in the call hangup event, regardless of whether the call was answered or missed.

{
  "uuid": "$uuid",
  "call_to_number": "$call_to_number",
  "caller_id_number": "$caller_id_number",

  // ... other webhook parameters ...
 
  "hangup_cause_description": "$hangupcause_desc",
  "hangup_cause_code": "$hangupcause_code",
  "hangup_cause_key": "$hangupcause_key"
}

Q.850 Cause Codes — Complete List with Details

Additional Resources

For further reference and deeper understanding of Q.850 hangup cause codes, mappings, and signaling behavior across telecommunication networks, the following resources are recommended:

• ITU-T Recommendation Q.850 (Official Standard) Defines the complete list of cause codes and their intended usage in Digital Signalling System No.1 (DSS1) and Signaling System No.7 (SS7 ISUP). https://www.itu.int/rec/T-REC-Q.850
• Asterisk Q.850 Cause Code Reference Practical descriptions commonly used in VoIP/PBX environments; useful for troubleshooting signaling and call routing issues. https://wiki.asterisk.org/wiki/display/AST/Q.850+Cause+Codes