Sorry Klaus, I pressed reply instead of reply to all so the mailist was not CCed, :-) I used the example configs v5 from Onsip.org and it didnt include an ACK handler. I added the extra code and no more warnings now. Also another thing i had to do when i was setting up the example config file for NAT and Media proxy was to add a check for NATed caller before the part of the below code in Invite handler: if (!proxy_authorize("","subscriber")) { proxy_challenge("","1"); break; } else if (!check_from()) { log (1,"route[3]: 403 error \n"); sl_send_reply("403", "Use From=ID"); break; }; Without the check and the fixed contact , no UA behind NAT could make a call except from the UA that took port 5060 on NAT. I also found that in my config file when a caller was behind nat and was trying to make a pstn call , i called use_media_proxy twice. When i fixed that , the calls would go through ok and not get a 503 response. Can someone explain what exactly happened when i called the use_media_proxy twice and the calls were getting rejected? Many thanks, Kyriakos ----- Original Message ----- From: "Klaus Darilion" <klaus.mailinglists(a)pernau.at> To: "Kyriakos" <tank30(a)hotmail.com>om>; "ser users" <serusers(a)lists.iptel.org> Sent: Wednesday, November 09, 2005 4:48 PM Subject: Re: [Serusers] Calls from UAs behind NAT getting a 503 error... _______________________________________________ Serusers mailing list serusers(a)lists.iptel.org http://lists.iptel.org/mailman/listinfo/serusers