Hello Alex,
Thank you for your reply. Well, I'm interfacing with several PSTN
operators, and some of their networks' SIP endpoints (or other obscure IMS
entity there) are very picky in that if they don't like the capabilities
you serve for telephone-event (which is if they don't match theirs), then
the transaction is rejected with "488 SDP Parameter Error In SIP Request"
(or if it's a reply I'm sending, they will send a BYE immediately).
Trying to reason with them (the operators) has failed, my SIP UA provides
no way to choose these values when the SDP is created (and since it
apparently has to match the other side some static configuration wouldn't
do much here), so all I'm left with is the option of growing my config file
by yet another 50 lines... :-\
BR,
George
On Mon, 1 Jun 2020 at 14:41, Alex Balashov <abalashov(a)evaristesys.com>
wrote:
George,
It may be orthogonal to the answer that you seek, but I’m going to ask
anyway: what is the overall motive underlying your SDP manipulation?
It seems to me that one should reason backward from that root cause. The
kind of SDP manipulation you are doing is seldom necessary in ordinarily
imaginable contexts...
— Alex
—
Sent from mobile, with due apologies for brevity and errors.
On Jun 1, 2020, at 7:35 AM, George Diamantopoulos <georgediam(a)gmail.com>
wrote:
Hello all,
I'm facing one of those cases where I need to edit the body of a SIP
message, which is then to be fed to rtpengine for processing. Although I've
taken every precaution I've read about on this list and elsewhere, I can't
prevent the edited line from appearing twice in the outgoing message.
The configuration file used is huge, so I'm going to try to provide a
high-level overview here. But first, the things (I think) I know to be
requirements, and which I have striven to meet:
- If SDP is to be edited, then all such processing is to be carried
out in such a way in the script, so that msg_apply_changes() is run as many
times as needed before rtpengine offer/answer/manage is called.
- rtpengine offer/answer/manage is to be called only once per script
iteration
- msg_apply_changes can only be called in a request route, or in the
core reply_route (i.e. *not* in tm-managed on_reply_route[XXX] blocks)
In my case, additionally the following are true:
- SDP processing (other than the one performed by rtpengine) takes
place in one common route for all cases where it needs to happen. These are
two at the moment in my scenario:
- Early in the WITHINDLG route (of the example config file)
- After the sanity checks in the reply_route (of the example config
file)
- msg_apply changes() is called once, for each script iteration:
- right before rtpengine_manage() is called, provided that
t_is_request_route() returns true (so that I don't accidentally call it
from a branch route or anything)
- rtpengine_manage() is called in its own route, which is very
similar to the example config file's "NATMANAGE" route. Since
NATMANAGE is
called in all branch and on_reply_routes, I employ t_is_request_route()
here to make sure it won't execute in those cases.
- at the end of the "core" reply_route
Now regarding the actual config-file-controlled SDP manipulation, it only
consists of a single call to replace_body_str(). The purpose is to edit a
line in the message body from something like:
- a=fmtp:101 0-16
to something along the lines of:
- a=fmtp:101 0-15
For replies, this works as expected.
For in-dialog requests, however, I end up with both the original and the
edited lines:
a=fmtp:101 0-16 (the original line)
... other SDP stuff ...
a=fmtp:101 0-15 (the edited line)
If anyone could point out any misconceptions I have about
msg_apply_changes, SDP rewriting from the script and rtp_engine_X()
interoperability, I would be more than grateful.
Thank you in advance and I apologize for the long read.
Best regards,
George Diamantopoulos
_______________________________________________
Kamailio (SER) - Users Mailing List
sr-users(a)lists.kamailio.org
https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users
_______________________________________________
Kamailio (SER) - Users Mailing List
sr-users(a)lists.kamailio.org
https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users