Thanks all - yes, my query was about audio/video/screensharing.. and I understood that for those SIP is prone to problems on the router-level, NAT - RIP - BGP etc - on which I am not expert (anymore )
If this is the case, how to set up such videoconferences from NATs with jitsi?
If instead a SIP is good, maybe I just got accounts on a bogus server (onsip.com) that does not deal properly with it… (?)
I realize the question should to be rather common ( I.e. how to replace skype) so I would expect the answer to be simple …
thanks for the discussion..