Dialogic Global Call IP Benutzerhandbuch

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outbound proxy configuration. Global Call also allows the application to change the contact URI 
scheme to be different than the initial INVITE by setting the complete contact header as described 
in 

For out-of-call request messages, such as REGISTER, OPTIONS, INFO, and 
SUBSCRIBE/NOTIFY, the transport method depends on the destination address URI scheme as 
well as the default transport protocol and any outbound proxy configuration.

If a TLS connection fails to establish due to a timeout, a network error, or some other reason, 
Global Call notifies the application with a GCEV_EXTENSION event with extension ID 
IPEXTID_RECEIVEMSG. The metadata for this extension event will contain a parameter of type 
IPSET_SIP_REQUEST_ERROR / IPPARM_SIP_SVC_UNAVAIL whose data is a 
REQUEST_ERROR data structure with the error code IP_SIP_NETWORK_ERROR. 

Unlike TCP connection failure, Global Call will not retry the transaction using UDP if the TLS 
connection fails, regardless of the value of the E_SIP_RequestRetry parameter in the 
IP_VIRTBOARD structure.

Common causes of connection failure include:

remote UA does not support TLS

TLS negotiation fails

post-connection assertion fails (TLS negotiation succeeds but remote TLS certificate hostname 
does not match request URI hostname)

certificate has been revoked or is outdated

The Dialogic

®

 Global Call API library provides six APIs specifically for call transfer in the IP 

technology. These APIs are described in the Dialogic

 Global Call API Library Reference with 

protocol-specific variances described in the subsections of 

. This section describes general considerations for implementing call 

transfer as well as details specific to H.450.2 (part of the H.323 protocol suite) and SIP protocols. 
For H.450.2-specific call transfer scenarios see 

, on page 57, and for SIP-specific call transfer scenarios, see 

, on page 74. The topics covered here include: