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Global Call IP Technology Guide — November 2007 173
Dialogic Corporation
IP-Specific Operations
Once the GC_PARM_BLK is composed, the application can pass that parm block as a parameter in
a Global Call function that directly sends a message (such as gc_Extension( ), which is used to
send messages like INFO or OPTIONS, or gc_ReqService( ), which is used to send REGISTER
requests) or can preset the header fields for the next message to be sent by calling the
gc_SetUserInfo( ) function. The use of gc_SetUserInfo( ) to preset SIP message header fields for
the next message is only recommended when using gc_MakeCall( ). For messages that are sent
directly (using gc_Extension( ), for example) the preferred method is to pass the parameter block
directly to the function, because a preset header is always used for the very next message sent,
which might not be the intended message. When using gc_SetUserInfo( ) to preset SIP message
header fields, the duration parameter must be set to GC_SINGLECALL, and the information is
not transmitted until the next Global Call function that sends a SIP message is issued.
Table 8 shows the relationship between some of the most common SIP header fields, the SIP
messages that commonly use them, and the Global Call functions that are used to set the headers
and send the message.
Note: The Dialogic
®
Global Call API library handles the SIP Request-URI exactly like a standard SIP
header field even though it is technically distinct from the header fields in a SIP message.
Table 8. Common Header Fields in Outbound SIP Messages
SIP header field SIP message Global Call function to set / send message
Accept OPTIONS gc_Extension( ) if E_SIP_OPTIONS_Access is
enabled
Accept-Encoding OPTIONS gc_Extension( ) if E_SIP_OPTIONS_Access is
enabled
Accept-Language OPTIONS gc_Extension( ) if E_SIP_OPTIONS_Access is
enabled
Allow OPTIONS gc_Extension( ) if E_SIP_OPTIONS_Access is
enabled
Call-ID INVITE gc_SetUserInfo( ) / gc_MakeCall( )
INFO, NOTIFY, SUBSCRIBE gc_Extension( )
OPTIONS gc_Extension( ) if E_SIP_OPTIONS_Access is
enabled
Contact
(display string and URI
separately accessible
separately using field-
specific parameters)
INVITE gc_SetUserInfo( ) / gc_MakeCall( )
INFO, NOTIFY, SUBSCRIBE gc_Extension( )
REFER gc_SetUserInfo( ) / gc_InvokeXfer( ) if call
transfer is enabled
OPTIONS gc_Extension( ) if E_SIP_OPTIONS_Access is
enabled
REGISTER gc_ReqService( )
Content-Disposition INFO gc_Extension( )
Content-Encoding INFO gc_Extension( )
Content-Length INFO gc_Extension( )
Content-Type INFO gc_Extension( )
‡ From and To header fields are not set in INVITE messages using SIP message information parameters.