SIP User's Manual
394
Document #: LTRT-68808
Mediant
2000
9.2
Release Reason Mapping
This section describes the available mapping mechanisms of SIP responses to Q.850
Release Causes and vice versa. The existing mapping of ISDN Release Causes to SIP
Responses is described in ''Fixed Mapping of ISDN Release Reason to SIP Response'' on
page
and ''Fixed Mapping of SIP Response to ISDN Release Reason'' on page
. To
override this hard-coded mapping and flexibly map SIP responses to ISDN Release
Causes, use the
ini
file (CauseMapISDN2SIP and CauseMapSIP2ISDN, as described in
''ISDN and CAS Interworking-Related Parameters'' on page
) or the Web interface (refer
to ''Release Cause Mapping'' on page
It is also possible to map the less commonly used SIP responses to a single default ISDN
Release Cause. Use the parameter DefaultCauseMapISDN2IP (described in ''ISDN and
CAS Interworking-Related Parameters'' on page
) to define a default ISDN Cause that is
always used except when 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 for Tel-to-IP calls.
9.2.1
Reason Header
The device supports the Reason header according to RFC 3326. The Reason header
conveys information describing the disconnection cause of a call:
Sending Reason header:
If a call is disconnected from the Tel side (ISDN), the
Reason header 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 a SIP 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 SIP
message includes the Reason header, it is sent to the Tel side according to the
following logic:
•
If the Reason header includes a Q.850 cause, it is sent as is.
•
If the Reason header includes a SIP response:
♦
If the message is a final response, the response status code is translated to
Q.850 format and passed to ISDN.
♦
If the message isn’t a final response, it is translated to a Q.850 cause.
•
When the Reason header is received twice (i.e., SIP Reason and Q.850), the
Q.850 takes precedence over the SIP reason and is sent to the Tel side.
9.2.2
Fixed Mapping of ISDN Release Reason to SIP Response
The following table describes the mapping of ISDN release reason to SIP response.
Table
9-1: Mapping of ISDN Release Reason to SIP Response
ISDN
Release
Reason
Description
SIP
Response
Description
1
Unallocated number
404
Not found
2
No route to network
404
Not found
3
No route to destination
404
Not found
6 Channel
unacceptable
406
*
Not
acceptable
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