Eric,
I think you should just try out the example RTP config in the nathelper directory. It is this one:
# main routing logic
route{
# compulsory processing of Route header fields and adding RR loose_route();
# ATA's are symmetric but don't advertise it -- force use of rport if (search("User-Agent: Cisco ATA.*")) { setflag(1); # remember this is ATA force_rport(); fix_nated_contact(); };
/* registration (uses rewritten contacts) */ if (method=="REGISTER") { save("location"); break; };
if (method=="INVITE") { record_route(); if (isflagset(1)) { # ATA ? force_rtp_proxy(); }; /* set up reply processing */ t_on_reply("1"); };
if (method == "INVITE" || method == "CANCEL") { if (!lookup("location")) { sl_send_reply("404", "Not Found"); break; }; };
/* set up reply processing and forward statefuly */ t_relay(); }
# all incoming replies for t_onrepli-ed transactions enter here onreply_route[1] { if (status=~"2[0-9][0-9]" && search("Server: Cisco ATA.*")) fix_nated_contact(); force_rtp_proxy(); }