I have Trixbox PBX and Cisco 3725 Router. Both of them are in same lan. My router has E1 interface that is connected to LG-PBX. My LG-PBX agent can call Trixbox agent directly over PRI. But when trixbox user try to call LG-PBX agent i take "SIP/2.0 488 Not Acceptable Media error" on cisco router. I am sending "debug ccsip messages" command output and trixbox "debug channels" output. Which option could cause this problem on Trixbox. I changed some option like preffered codec,nat.. for Trixbox agent(500) and trunk(to PBX). But nothing change. Thanks for all replly.