Cellular Network Infrastructure » Core Network (CN) » osmo-sip-connector

During analysis of a pcap of a short call, I noticed that the final SIP ACK as well as BYE goes back to its own address.
This is using osmo-sip-connector and Kamailio

This is a text representation of the entire SIP negotiation,
the point being the last three 'SIP->(self)' in the end.

(MO -> sipcon -> kamailio -> sipcon -> MT)

        SIP2    sip.***New:SIP2=192.168.178.74:5069 452
SIP             sip.***New:SIP=192.168.178.74:5060 452
SIP--->SIP2     sip.INVITE udp{'src'='192.168.178.74:5060', 'dst'='192.168.178.74:5069'} 452
SIP<---SIP2     sip.INVITE-trying udp{'src'='192.168.178.74:5069', 'dst'='192.168.178.74:5060'} 460
SIP<---SIP2     sip.INVITE udp{'src'='192.168.178.74:5069', 'dst'='192.168.178.74:5060'} 462
SIP--->SIP2     sip.INVITE-Trying udp{'src'='192.168.178.74:5060', 'dst'='192.168.178.74:5069'} 469
SIP--->SIP2     sip.INVITE-Ringing udp{'src'='192.168.178.74:5060', 'dst'='192.168.178.74:5069'} 1200
SIP<---SIP2     sip.INVITE-Ringing udp{'src'='192.168.178.74:5069', 'dst'='192.168.178.74:5060'} 1202
SIP--->SIP2     sip.INVITE-OK udp{'src'='192.168.178.74:5060', 'dst'='192.168.178.74:5069'} 1324
SIP<---SIP2     sip.INVITE-OK udp{'src'='192.168.178.74:5069', 'dst'='192.168.178.74:5060'} 1328
SIP->(self)     sip.ACK udp{'src'='192.168.178.74:5060', 'dst'='192.168.178.74:5060'} 1353
SIP->(self)     sip.BYE udp{'src'='192.168.178.74:5060', 'dst'='192.168.178.74:5060'} 1702
SIP->(self)     sip.BYE-OK udp{'src'='192.168.178.74:5060', 'dst'='192.168.178.74:5060'} 1706

(the final numbers are the packet index in the attached pcap;
output generated by 'osmo-gsm-shark -f short_call_flt.pcapng --filter-msg sip --show-traits udp')

I'm not entirely sure whether that is intended, i.e. that Kamailio connects both peers and takes itself out of the loop (like it does with RTP),
and I can in fact find a 'Contact URI' in the SIP package that might intend to do that, but it has no port number?
Or is it the 'Via' header ... ?

Figure this out to see whether osmo-sip-connector has a bug.