[SR-Users] How to disable retransmits via TCP connection? etc.

[Andrey Utkin]

Hi!
We meet such an issue with some kinds of client internet connections
(e.g. reproduces always on local wifi, but doesn't repr. on 3g inet).
We don't know what are exact network characteristics, but what happens
from perspective of traffic on SIP server is the following:

1. the SIP client registers successfully to Kamailio (which is recent
git master HEAD) with TCP transport for SIP;
2. another client calls this user;
3. Kamailio relays INVITE, it gets transmitted fully and ACK-ed on TCP level;
4. then, within 0.1-0.2 second, Kamailio fires first retransmit of
that INVITE, which doesn't get fully transmitted (it is shown
trunkated in sniffer output, no TCP ACK replies for it);
5. Kamailio tries to retransmit INVITE again, with the same result as in #5.
6. The caller gets SIP/2.0 408 Request Timeout.

A piece of traffic from "ngrep -t -e -d any -W byline port 5060":
https://gist.githubusercontent.com/krieger-od/219f9975e5efb980ff5b/raw/096a639bf459b5f7c8a2a83eba8424f0dd3d22ea/gistfile1.txt

The called side app is based on mobile Linphone app.
Switching to UDP is not an option (in some networks SIP messages get
delivered trunkated which breaks calls), we will check how it works
with TLS transport a bit later when there's technical possibility.

I have two questions:
1. How would I completely disable retransmissions to TCP connections?
2. Any ideas what can be the reason for this issue? Retransmissions by
themselves?

-- 
Andrey Utkin