Ip address problem in asterisk


i am having problem with my incoming calls, because my trunk providers recently changed IP address.

It worked fine before. now, i have to set my asterisk box to receive calls from anonymous IP. If I set the IP from the designated IP only, I could Not receive incoming calls.

according to my trunk provider, while the SIP message IP should be fixed, the RTP IP could one of many IP, and should not be fixed.

could anybody tell me how to configure my asterisk? My engineer does not speak good english, it is difficult to communicate with the trunk provider directly.