Thanks Alain and Hari. >> > PRACK is different from ACK. It can do work of offer/answer in addition to acknowledging the provisional responses. ACK can also provide answer if 200 ok contains initial offer. Nevertheless they are similar but not same. -Thankyou -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.pjsip.org/pipermail/pjsip_lists.pjsip.org/attachments/20120117/e42405da/attachment.html>