>by using following command, pjsip should use tcp but is using udp >? ? ? ? ? ? ? ./pjsua-x86_64-unknown-linux-gnu --id sip:pjsip at 192.168.0.45--registrar sip:192.168.0.45:5061;transport=tcp --no-udp Your shell is eating everything after the semicolon, and you're ending up setting a shell variable transport to "tcp --no-udp". Put the registrar in quotes in your command line. -m@ -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.pjsip.org/pipermail/pjsip_lists.pjsip.org/attachments/20111029/53c889b3/attachment.html>