12 Mar
2005
12 Mar
'05
9:55 a.m.
See inline.
Java Rockx wrote:
Hi All.
I'm a confused when handling CANCEL messages when the call is between
my SER proxy and a PSTN gateway.
I've had a few discussions with Jan regarding when lookup("location")
needs to be called and as I understand it CANCEL is sort of an odd
message that is not really mid-dialog, and therefore not
record-routed. So lookup("location") needs to be called before
t_relay()ing a CANCEL.
A CANCEL only has a meaning before the final response (OK) is sent from the
other UA. The CANCEL is matched using CSeq. However, AFAIK CANCEL can also
be record-routed. It is only REGISTER messages that exclicitly (RFC3261)
should not be record routed as it does not establish a dialog. However,
record routing does not really help you with regards to lookup("location")
as record-routing will give you the answer (ex. Call leg does not exists
etc).
One thing though, even though CANCEL should be handled as an INVITE, CANCEL
cannot have authentication information and if your routing logic for CANCEL
triggers an authentication, the CANCEL will not reach its destination.
This is fine for calls between two UAs on the same SER
proxy since
both UAs have a contact record and lookup("location") will return
TRUE.
But when calling SIP->PSTN, and you hang up from the SIP side, the
CANCEL is sent from the SIP UA to SER. Then SER tries to find the
contact record in the location table, but since this is a PSTN
destination, lookup(location) returns false, thus a 404 and the CANCEL
is not relayed to the PSTN gateway.
So what is the best way to process CANCEL messages? Just ignore
lookup("location") when it returns false for CANCEL messages?
How do you handle INVITEs when lookup("location") fails? The request-URI
should be the same as the initial INVITE and you should thus be able to do
exactly the same with CANCELs. Even if you do lcr.
g-)
My basic ser.cfg is like this:
route {
# sanity checks
if (method!="REGISTER") record_route();
if (loose_route()) {
t_relay();
break;
};
if (uri!=myself) {
t_relay();
break;
};
if (uri==myself) {
if (method=="REGISTER") {
save("location");
break;
};
if (!lookup("location")) {
sl_send_reply("404", "Not Found");
break;
};
};
t_relay();
}
Regards,
Paul
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