Interworking SIP Response to ISUP Cause Values

If a Reason header as described in IETF RFC 6432 is included in a SIP 4xx, 5xx, 6xx response, and you have enabled the sip-config, sip-response-code parameter, theSBC maps the Cause Value of the Reason header to the ISUP Cause Value field in the REL message, as follows:

SIP Response	ISUP Cause Value
400, 414, 416, 420, 421	111 (Protocol Error, Unspecified)
403, 417, 501	79 (Not implemented, Unspecified)
404, 485	1 (Unallocated number)
408, 504	102 (Timer expiry)
410	22 (Number Changed)
422	31 (Normal, Unspecified)
433	24 (Call Rejected due to feature at destination)
480	20 (Subscriber Absent)
483	25 (Exchange routing Error)
484	28 (Invalid Number Format)
486, 600	17 (User Busy)
488	50 (Request Facility Not Supported)
502	27 (Destination Out of order)
503	41 (Temporary Failure)
513	95 (Invalid Message, Unspecified)
603	21 (Call Rejected)
604	2 (No route specified)
606	88 (Incompatible Destination)
Other	127 Interworking Unspecified)

For errors received from the SIP-I side, the SBC inserts a Reason Header into the SIP body, if it is not generated by some other process. This also requires that you have enabled the add-reason-header within the sip-config. The SBC inserts the SIP Reasons according to the ISUP Cause Value (cause attribute and reason) mapping from ITU-T Q.850.