we have discuss this issue in thread:
"SIP not working in Ubuntu 12.04.1 64b"
the conclusion was
1. JITSI should prefer usage of TCP (e.g. while UDP big packet fragmentation problem)
2. but NAPTR must allow this by priority setting
3. JITSI should use SIPS if available
Thanks great support of my SIP provider we had set it on server.
(before there was (100,50) for UDP and (200,50) for TCP -> ad.2 -> UDP was used)
$ host -t NAPTR sip.odorik.cz
sip.odorik.cz has NAPTR record 100 50 "s" "SIP+D2T" "" _sip._tcp.sip.odorik.cz.
sip.odorik.cz has NAPTR record 100 50 "s" "SIP+D2U" "" _sip._udp.sip.odorik.cz.
sip.odorik.cz has NAPTR record 100 51 "s" "SIPS+D2T" "" _sips._tcp.sip.odorik.cz.
But JITSI still uses UDP, not TCP - even if the choice is only and only on JITSI.
And the SIPS is not used too.
SIP client must respect first priority in NAPTR (100 < 200 in our cases in previous) but the second one is only recommendation and client can use it how he want.
Thats mean in current case:
UDP = 100.50
TCP = 100,50 or 100,51 or 100,whatever
JITSI should use TCP !
And if there is SIPS 100,51 then JITSI should use SIPS too (if configured to prefer encrypted connection).
But JITSI do not do that