4.2.13. gc_SndMsg( )

The gc_SndMsg( ) function enables sending of application-ISUP messages, as long as they do not alter the call state or circuit state.

Messages must be formatted as required by the SS7 stack. This format is very similar to the ISUP format with the exception that all message parameters are coded as optional parameters (parameter name, length and contents).

The ISUP message type (also know as primitive) is specified in the msg_type argument. The message parameters are specified in the S7_IE_BLK pointed to by the cclib field of the GC_IE_BLK given as an argument to this function. Multiple parameters can be put one after the other in the data field of the S7_IE_BLK structure. The total length of the parameters section must be set in the length field of the structure.

The following code fragment illustrates the use of gc_SndMsg( ) for SS7:

/* Send a Subsequent Address Message 
 * (SAM) with digits 234 (overlap sending) 
 */ 
S7_IE_BLK ie_blk; 
GC_IE_BLK gc_ie_blk;  
ie_blk.length = 5; 
ie_blk.data[0] = 0x05;  /* Parameter 1 name - Subsequent Number */ 
ie_blk.data[1] = 0x03;  /* Parameter 1 length - 3 bytes */ 
ie_blk.data[2] = 0x80;  /* Parameter 1 value - odd number of digits */ 
ie_blk.data[3] = 0x32;  /* Parameter 1 value - digits '2' and '3' */ 
ie_blk.data[4] = 0x04;  /* Parameter 1 value - digit  '4' */  
gc_ie_blk.gclib = NULL; 
gc_ie_blk.cclib = &ie_blk; 
ret = gc_SndMsg(linedev, crn, 0x02 /* SAM */, &gc_ie_blk);  

Note: Parameter values (for example, 0x05 which corresponds to the Subsequent Number parameter) should correspond to parameter values from the ISUP/TUP specifications. Similarly, message type values (for example, 0x02 in the gc_SndMsg( ) function call above) should correspond to message type values from the ISUP/TUP specification.

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