23 Jul
2020
23 Jul
'20
5:07 p.m.
Indeed, at this stage there is no dialog established and there can be
many To-tags in 1xx provisional responses (eg, a parallel forking
scenario) -- the to-tag of the dialog has to be taken from 200ok.
This parameter is probably to have a shortcut of doing:
failure_route[REMAP503] {
if(t_check_status("503")) {
t_reply("500", "Server error");
exit;
}
Being like the server application is generating the 500 (so using own
tag), instead of forwarding the 503. Not a bug, but if anyone is willing
to add an option to allow re-using the to-tag from received reply, I am
fine with it.
Anyhow, even if this would be fixed, I am wondering how yate is going to
work in parallel/serial forking scenarios where different to-tags flow
for a while and the final failure response can have any to-tag,
including a new one (e.g., from a device not sending any 1xx or again
from kamailio (e.g., when last target doesn't reply at all)).
Cheers,
Daniel
On 23.07.20 06:08, M S wrote:
The SIP code 503 is tricky in the sense that i can
indicate either
server maintenance or server overload. In both cases it can send
Retry-After header and any subsequent requests from same source are
ignored for the duration of Retry-After interval. [1].
Additionally RFC3261 and RFC3263 define that transport failures
(generally due to fatal ICMP errors in UDP and connection failures in
TCP) should be treated as 503 response. [2].
So in all above cases, it is most likely that dialog does not
establishes at all and 503 response is treated similar to stateless
response. Therefore, a to-tag can be added/replaced before sending it
to UAC.
Theoretically, kamailio should check and use to-tag from 503 response
when converting it to 500 response and only create new to-tag if it is
absent.
References:
[1] https://tools.ietf.org/html/rfc3261#section-21.5.4
[2] https://tools.ietf.org/html/draft-hilt-sip-correction-503-01#section-4
Hope this helps.
On Wed, 22 Jul 2020 at 21:08, Henning Westerholt <hw(a)skalatan.de
<mailto:hw@skalatan.de>> wrote:
Hello,
Apparently, this is the way the code works:
t_reply.c:
if (relayed_code==503 && tm_remap_503_500){
/* replace a final 503 with a 500:
* generate a "FAKE" reply and a
new to_tag (for easier
* debugging)*/
Lets see if maybe others can comment as well. Otherwise you could
just open an issue on our tracker, it is probably not that hard to
change this.
Cheers,
Henning
--
Henning Westerholt – https://skalatan.de/blog/
Kamailio services – https://gilawa.com <https://gilawa.com/>
*From:* sr-users <sr-users-bounces(a)lists.kamailio.org
<mailto:sr-users-bounces@lists.kamailio.org>> *On Behalf Of *Gerry
| Rigatta
*Sent:* Wednesday, July 22, 2020 8:58 PM
*To:* Kamailio (SER) - Users Mailing List
<sr-users(a)lists.kamailio.org <mailto:sr-users@lists.kamailio.org>>
*Subject:* [SR-Users] bug ? remap_503_500 breaks dialogs
Hi,
I am using Kamailio 5.2.
Apparently the remapping of 503 to 500 codes in the tm module does
also change the to-tag. This behaviour breaks dialogs with yate
and therefore calls hang and the 503 remains unacknowledged. After
disabling the 503 to 500 remapping with modparam("tm",
"remap_503_500", 0) all works fine again.
Changing the to-tag in a dialog seems to contradict RFC3261, or do
I see this wrongly?
12<https://tools.ietf.org/html/rfc3261#section-12>Dialogs
A dialog is identified at each UA with a dialog ID, which
consists of a Call-ID value, a local tag and a remote tag…"
Thanks for looking into this.
Gerry
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