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Global Call IP Technology Guide — November 2007 175
Dialogic Corporation
IP-Specific Operations
Header Fields in Incoming SIP Messages
For incoming SIP messages, the Dialogic
®
Global Call API library packages the header fields that
the application has registered to receive as parameters in the GC_PARM_BLK that is associated
with the Global Call event that notifies the application of the message. The application retrieves the
parameter block by calling gc_GetMetaEvent( ), and can then extract the contents of the various
header fields from the GC_PARM_BLK. The application must complete the retrieval of the
necessary SIP message header information (for example, by copying it into its own buffer) before
the next call to gc_GetMetaEvent( ), since the parameter block is no longer available from the
metaevent buffer once the next gc_GetMetaEvent( ) call is issued.
In addition to the header fields that the application specifically registers to receive, the
GC_PARM_BLK for a message-related Global Call event may contain one or more of the header-
specific parameters that were used in the previous header access methodology. It is important to
note that these parameters are limited to a 255 byte data length and may potentially contain a
truncation of the a header field’s contents.
Table 9 lists some common SIP header fields along with the SIP message that commonly contains
them and the Global Call event that is used to convey the message information to the application.
Note: The From URI and To URI in incoming INVITE messages are accessible using the
gc_GetCallInfo( ) function; see Section 8.3.10, “gc_GetCallInfo( ) Variances for IP”, on page 452,
for more information. In all other cases, applications must access the complete From and To header
fields in order to access the URIs.
To
(display string
separately accessible
via field-specific
parameter)
INVITE gc_SetUserInfo( ) / gc_MakeCall( )
INFO, NOTIFY, SUBSCRIBE gc_Extension( )
OPTIONS gc_Extension( ) if E_SIP_OPTIONS_Access is
enabled
REFER gc_SetUserInfo( ) / gc_InvokeXfer( ) if call
transfer is enabled
REGISTER gc_ReqService( )
Table 8. Common Header Fields in Outbound SIP Messages (Continued)
SIP header field SIP message Global Call function to set / send message
‡ From and To header fields are not set in INVITE messages using SIP message information parameters.
Table 9. Common Header Fields in Inbound SIP Messages
SIP header SIP message Global Call event
Accept OPTIONS GCEV_EXTENSION if
E_SIP_OPTIONS_Access is enabled
Accept-Encoding OPTIONS GCEV_EXTENSION if
E_SIP_OPTIONS_Access is enabled
Accept-Language OPTIONS GCEV_EXTENSION if
E_SIP_OPTIONS_Access is enabled
† Header field also accessible via field-specific parameter define.
‡ From and To header fields are not retrieved from INVITE messages using SIP message information parameters.