I don't have a tremendous amount of time so this is going to be a short one.
There is a CANCEL related bug in Asterisk 1.4.23 versions. To be honest I'm not sure when it was introduced but I know when it was fixed:
http://bugs.digium.com/view.php?id=14431
This caused trouble for me because I often use Asterisk in tandem with OpenSIPS and FreeSWITCH. Both platforms were unable to match the CANCEL sent by Asterisk to the original INVITE. As the bug note says, this is because the CANCEL sent by Asterisk had a different branch parameter than the original INVITE. OpenSER/OpenSIPS would fail when checking t_check_trans()as long as method==CANCEL.
FreeSWITCH was a *little* easier to diagnose because it would send a 481. I suppose I could have made (and should make) my OpenSIPS configurations do this when using t_check_trans for CANCEL:
if (is_method("CANCEL")) {
if (!t_check_trans()) {
# No matching transaction, error and exit
sl_send_reply("481","Call leg/transaction does not exist");
exit;
}
# Hand it to tm
t_relay();
exit;
Anyways this has certainly been fixed in Asterisk 1.4.24. I'm looking forward to not dealing with any of this for some time...
