[asterisk-dev] AST_FRAME_NULL - what is it?

[Bryan Field-Elliot]

We are running a simple custom application on Asterisk 1.6.1, which  
basically waits for a DTMF digit to be entered by the user.

Our code is basically like this:

struct ast_frame *frame;
while (true) {
	ast_waitfor(channel, -1);
	frame = ast_read(channel);
	// Exit if hung up
	if (frame->frametype == AST_FRAME_CONTROL) && (f->subclass ==  
AST_CONTROL_HANGUP)) {
		ast_frfree(frame);
		return;
	}
	if (frame->frametype == AST_FRAME_DTMF) {
		// .. Do the thing we need with the digit ...
		ast_frfree(frame);
		return;
	}
	// Ignore the frame, it's not a DTMF digit.
	ast_frfree(frame);
}

Most of our clients are SIP clients, and this loop ends up ignoring a  
few hundred frames before the user enters a digit. That's fine. But  
some of our SIP clients, when they execute this, end up throwing us  
around 150,000 AST_FRAME_NULL's, which this little loop has to ignore.  
I don't know why Asterisk is sending us the AST_FRAME_NULL's or what  
it's supposed to mean, but, our CPU is getting pegged from having to  
process and ignore all those frames. CPU is NOT pegged when a SIP  
client connects which is not sending us these null frames.

Can anyone please advise why this is happening, and how we can get it  
to stop?