[Asterisk-Dev] Specific question about pri_dchannel in channels/chan_zap.c

[Chris Ziomkowski]

I have a more specific question in my quest to understand the internals of 
asterisk and implement R2 outbound dialing.

Specifically, given a PRI channel (on a Digium digital span card) dialing 
out, it appears that the ANSWER message will be read by the function 
pri_dchannel in channels/chan_zap.c at or around line 5806.

My question is, how does an application (such as Dial) which is blocked in 
an ast_select() on the channel actually get informed of 
this?  (apps/app_dial.c in wait_for_answer() at or around line 177)

The way I read the code, the only thing that happens is that a flag 
"needanswer" is set on the channel. I was expecting to see some kind of 
code which would cause an event to appear on a file descriptor and wake up 
an application blocked in a select waiting for events.

Can someone explain to me how the Dial application works with PRI?

I am obviously missing something.

Thanks for any assistance,

Chris Ziomkowski
cziom at jsg.co.th