4.5. Retrieving Current Call-Related Information

To support large numbers of channels, the call control library must perform all operations in asynchronous mode. To support this, an extension function variant allows the retrieval of a parameter as an asynchronous operation.

The retrieval of call-related information is a four step process:

• Set up a GC_PARM_BLK that identifies which information is to be retrieved. The GC_PARM_BLK includes GC_PARM_DATA blocks. The GC_PARM_DATA blocks specify only the Set_ID and Parm_ID fields, that is, the value_size field is set to 0. The list of GC_PARM_DATA blocks indicate to the call control library the parameters to be retrieved.
• Use the gc_Extension( ) function to request the data. The target_type should be GCTGT_GCLIB_CRN and the target_id should be the actual CRN. The ext_id function parameter (extension ID) should be set to IPEXTID_GETINFO, the parmblkp function parameter should point to the GC_PARM_BLK set up in step 1, and the mode function parameter should be set to EV_ASYNC (asynchronous).
• A GCEV_EXTENSIONCMPLT event is generated in response to the gc_Extension( ) request. The extevtdatap field in the METAEVENT structure for the GCEV_EXTENSIONCMPLT event is a pointer to an EXTENSIONEVTBLK structure that contains a GC_PARM_BLK with the requested call-related information.
• Extract the information from the GC_PARM_BLK associated with the GCEV_EXTENSIONCMPLT event. In this case, the GC_PARM_BLK contains real data, that is, the value_size field is not 0, but includes the size of the data following for each parameter requested.

Table 9 shows the parameters that can be retrieved and when the information should be retrieved. The table also identifies which information can be retrieved when using H.323 and which information can be retrieved using SIP.

Table 9. Retrievable Call Information

Para-meter	Set ID	Parameter ID	When Information Can Be Retrieved	Datatype in value_ buf Field (See Note Below)	H.323/SIP
Call ID	IPSET_CALLINFO	IPPARM_CALLID	Any state after Offered or Proceeding.	String,max. length = IP_CALLID_LENGHT (16 octets)	H.323 only
Call Duration	IPSET_CALLINFO	IPPARM_CALLDURATION	After Disconnected, before Idle.	Unsigned long (value in ms)	H.323 only
Conference Goal	IPSET_CONFERENCE	IPPARM_CONFERENCE_GOAL	Any state after Offered or Proceeding.	Uint[8]	H.323 only
Conference ID	IPSET_CONFERENCE	IPPARM_CONFERENCE_ID	Any state after Offered or Proceeding.	char*, max. length = IP_CONFERENCE_ID_LENGTH (16)	H.323 only
Display Information	IPSET_CALLINFO	IPPARM_DISPLAY	Any state after Offered or Proceeding.	char*,max. length = MAX_DISPLAY_LENGTH (82), null-terminated	H.323 and SIP
Nonstandard Control	IPSET_NONSTANDARDCONTROL	IPPARM_NONSTANDARDDATA_DATA IPPARM_NONSTANDARDDATA_OBJID or IPPARM_H221NONSTANDARD	See Section 4.5.1, Retrieving Nonstandard Data From Protocol Messages When Using H.323 for more information.	char*, max. length = MAX_NS_PARM_DATA_LENGHT (128) char*, max. length = MAX_NS_PARM_OBJID_LENGHT (40)	H.323 only
Nonstandard Data	IPSET_NONSTANDARDDATA	IPPARM_NONSTANDARDDATA_DATA IPPARM_NONSTANDARDDATA_OBJID or IPPARM_H221NONSTANDARD	See Section 4.5.1, Retrieving Nonstandard Data From Protocol Messages When Using H.323 for more information.	char*, max. length = MAX_NS_PARM_DATA_LENGHT (128) char*, max. length = MAX_NS_PARM_OBJID_LENGHT (40)	H.323 only
Phone List	IPSET_CALLINFO	IPPARM_PHONELIST	Any state after Offered or Proceeding.	char*,maximum length = 131	H.323 and SIP
User to User Information	IPSET_CALLINFO	IPPARM_USERUSER_INFO	Any state after Offered or Proceeding.	char*,max. length = MAX_USERUSER_INFO_LENGTH (131 octets)	H.323 only
Vendor Product ID	IPSET_VENDORINFO	IPPARM_VENDOR_PRODUCT_ID	Any state after Offered or Proceeding.	char*,maximum length = MAX_PRODUCT_ID_LENGTH (32)	H.323 only
Vendor Version ID	IPSET_VENDORINFO	IPPARM_VENDOR_VERSION_ID	Any state after Offered or Proceeding.	char*,maximum length = MAX_VERSION_ID_LENGTH (32)	H.323 only
H.221 Nonstandard Information	IPSET_VENDORINFO	IPPARM_H221NONSTD	Any state after Offered or Proceeding.	IP_H221_NON STANDARD(see note 4)	H.323 only
Notes: 1. This field is the value_buf field in the GC_PARM_DATA structure associated with the GCEV_EXTENSIONCMPLT event generated in response to the gc_Extension( ) function requesting the information. 2. Display information, user to user information, phone list, nonstandard data, vendor information and nonstandard control information, and H221 nonstandard information may not be present. 3.Vendor information is included in a Q931 SETUP message received from a peer. 4. The nonstandard object id and nonstandard data parameters described here refer to nonstandard data contained in a SETUP message for example. This should not be confused with the nonstandard data included in protocol messages sent using gc_Extension( ) which can be retrieved from the metaevent associated with a GCEV_EXTENSION event.

If an attempt is made to retrieve information in a state in which the information is not available, no error is generated. The GC_PARM_BLK associated with the generated GCEV_EXTENSIONCMPLT event will not contain the requested information. If phone list and display information are requested and only phone list is available, then only phone list information is available in the GC_PARM_BLK. An error is generated if there is an internal error (such as memory cannot be allocated).

All call information is available until a gc_ReleaseCall( ) is issued.

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