454 V7122 GatewayUser GuideAPPENDIX H: RELEASE R EASON M APPINGThis appendix describes the available mapping mechanisms of SIP Responses to Q.850Release Causes and vice versa.Table 97 and Table 98 describe the existing mapping of ISDN Release Causes to SIPResponses. To override this hard-coded mapping and flexibly map SIP Responses to ISDNRelease Causes use the parameters CauseMapISDN2SIP and CauseMapSIP2ISDN(described in ISDN and CAS Interworking-Related Parameters), or using the EmbeddedWeb Server (see Release Cause Mapping).It is also possible to map the less commonly-used SIP Responses to a single default ISDNRelease Cause. Use the parameter DefaultCauseMapISDN2IP (described in ISDN and CASInterworking-Related Parameters) to define a default ISDN Cause that is always used exceptwhen the following Release Causes are received: Normal Call Clearing (16), User Busy (17),No User Responding (18) or No Answer from User (19). This mechanism is only available forTel to IP calls.Reason HeaderThe gateway supports the Reason header according to RFC 3326. The Reason header isused to convey information describing the disconnection cause of a call: Sending Reason header: If a call is disconnected from the Tel side (ISDN), the Reasonheader is set to the received Q.850 cause in the appropriate message (BYE / CANCEL /final failure response) and sent to the SIP side. If the call is disconnected because of aSIP reason, the Reason header is set to the appropriate SIP response. Receiving Reason header: If a call is disconnected from the IP side and the SIPmessage includes the Reason header, it is sent to the Tel side according to the followinglogic: If the Reason header includes a Q.850 cause, it is sent as is. If the Reason header includes a SIP response: (1) If the message is a final response,the response status code is translated to Q.850 format and passed to ISDN. (2) If themessage isn’t a final response, it is translated to a Q.850 cause. When the Reason header is received twice (that is, SIP Reason and Q.850), theQ.850 takes precedence over the SIP reason and is sent to the Tel side.
