Calls Requiring IWF

For interworking calls between SIP and H.323, you can configure:

Mappings for SIP status codes to Q.850 values
Mappings for particular Q.850 cause codes to SIP status codes

If it cannot find the appropriate mapping, then the Oracle® Enterprise Session Border Controller uses default mappings defined in the Default Mappings table below.

The following describes how the Oracle® Enterprise Session Border Controller handles different IWF call scenarios:

SIP request containing a Reason header—When it receives a request containing a Reason header, the Oracle® Enterprise Session Border Controller determines if the request is a SIP BYE or SIP CANCEL message. RFC 3326 states that the Reason header is mainly used for these types of requests. If there is a Reason header and it contains the Q.850 cause value, then the Oracle® Enterprise Session Border Controller releases the call on the H.323 side using the specified cause value.
SIP response—When it receives the error response to an initial SIP INVITE, the Oracle® Enterprise Session Border Controller uses its SIP-Q.850 map to determine the Q.850 that it will use to release the call. If there is not a map entry, then the Oracle® Enterprise Session Border Controller uses the default mappings shown in the Default Mappings table.
Active call released from the H.323 side—If an active call is released from the H.323 side, the Oracle® Enterprise Session Border Controller checks the outgoing realm (the SIP side) to see if the addition of the Reason header is enabled. If it is, then the Oracle® Enterprise Session Border Controller adds the Reason header in the SIP BYE request with the Q.850 value it received from the H.323 side.
Error during setup of the call on the H.323 side—In the event of an error during setup on the H.323 side of the call, the system needs to send:
- An error response, if this is a SIP to H.323 call
- A SIP CANCEL, if this is a H.323 to SIP call and the H.323 side hangs up before the call is answered on the SIP side
  In this case, the Oracle® Enterprise Session Border Controller checks to see if adding the Reason header is enabled in the IWF configuration. If it is, then the Oracle® Enterprise Session Border Controller adds the Reason header with the Q.850 cause value it received from the H.323 side.
Call released due to a Oracle® Enterprise Session Border Controller error—If the call is released due a Oracle® Enterprise Session Border Controller error and adding the Reason header is enabled in the IWF configuration, the error response to the initial INVITE contains the Reason header. The Oracle® Enterprise Session Border Controller checks the SIP to Q.850 map configurations to determine whether or not the SIP error response code it is generating is configured. If it is, then the Oracle® Enterprise Session Border Controller maps according to the configuration. If if it not, the Oracle® Enterprise Session Border Controller derives cause mapping from the default table.

Like the configuration for SIP-only calls that enable this feature, you can set a parameter in the IWF configuration that enables adding the Reason header in the SIP requests or responses.