I installed centos 6.3, mediaproxy 2.5.2, opensips 1.8.2.

I use osipsconfig generate opensips.cfg

Opensips and mediaproxy  run at public, no NAT or firewall.
#
# $Id: opensips_residential.m4 9042 2012-05-17 13:57:10Z vladut-paiu $
#
# OpenSIPS residential configuration script
#     by OpenSIPS Solutions <team@opensips-solutions.com>
#
# This script was generated via "make menuconfig", from
#   the "Residential" scenario.
# You can enable / disable more features / functionalities by
#   re-generating the scenario with different options.#
#
# Please refer to the Core CookBook at:
#      http://www.opensips.org/Resources/DocsCookbooks
# for a explanation of possible statements, functions and parameters.
#

####### Global Parameters #########

debug=3
log_stderror=no
log_facility=LOG_LOCAL0

fork=yes
children=4

/* uncomment the following lines to enable debugging */
#debug=6
#fork=no
#log_stderror=yes

/* uncomment the next line to enable the auto temporary blacklisting of
   not available destinations (default disabled) */
#disable_dns_blacklist=no

/* uncomment the next line to enable IPv6 lookup after IPv4 dns
   lookup failures (default disabled) */
#dns_try_ipv6=yes

/* comment the next line to enable the auto discovery of local aliases
   based on revers DNS on IPs */
auto_aliases=no

listen=udp:180.168.138.213:5060   # CUSTOMIZE ME

disable_tcp=no
listen=tcp:180.168.138.213:5060   # CUSTOMIZE ME

disable_tls=yes

####### Modules Section ########

#set module path
mpath="/usr/local/opensips_1.8.2/lib64/opensips/modules/"

#### SIGNALING module
loadmodule "signaling.so"

#### StateLess module
loadmodule "sl.so"

#### Transaction Module
loadmodule "tm.so"
modparam("tm", "fr_timer", 5)
modparam("tm", "fr_inv_timer", 30)
modparam("tm", "restart_fr_on_each_reply", 0)
modparam("tm", "onreply_avp_mode", 1)

#### Record Route Module
loadmodule "rr.so"
/* do not append from tag to the RR (no need for this script) */
modparam("rr", "append_fromtag", 0)

#### MAX ForWarD module
loadmodule "maxfwd.so"

#### SIP MSG OPerationS module
loadmodule "sipmsgops.so"

#### FIFO Management Interface
loadmodule "mi_fifo.so"
modparam("mi_fifo", "fifo_name", "/tmp/opensips_fifo")
modparam("mi_fifo", "fifo_mode", 0666)

loadmodule "mi_datagram.so"
modparam("mi_datagram", "socket_name", "/var/run/opensips/socket")
modparam("mi_datagram", "children_count", 1)
modparam("mi_datagram", "unix_socket_mode", 0666)

#### URI module
loadmodule "uri.so"
modparam("uri", "use_uri_table", 0)
modparam("uri", "db_url", "mysql://opensips:opensipsrw@localhost/opensips")

#### MYSQL module
loadmodule "db_mysql.so"

#### USeR LOCation module
loadmodule "usrloc.so"
modparam("usrloc", "nat_bflag", 10)
modparam("usrloc", "db_mode",   2)
modparam("usrloc", "db_url",
"mysql://opensips:opensipsrw@localhost/opensips") # CUSTOMIZE ME

#### REGISTRAR module
loadmodule "registrar.so"
modparam("registrar", "tcp_persistent_flag", 7)
modparam("registrar", "received_avp", "$avp(received_nh)")
/* uncomment the next line not to allow more than 10 contacts per AOR */
#modparam("registrar", "max_contacts", 10)

#### ACCounting module
loadmodule "acc.so"
/* what special events should be accounted ? */
modparam("acc", "early_media", 0)
modparam("acc", "report_cancels", 0)
/* by default we do not adjust the direct of the sequential requests.
   if you enable this parameter, be sure the enable "append_fromtag"
   in "rr" module */
modparam("acc", "detect_direction", 0)
modparam("acc", "failed_transaction_flag", 3)
/* account triggers (flags) */
modparam("acc", "db_flag", 1)
modparam("acc", "db_missed_flag", 2)
modparam("acc", "db_url",
"mysql://opensips:opensipsrw@localhost/opensips") # CUSTOMIZE ME

#### AUTHentication modules
loadmodule "auth.so"
loadmodule "auth_db.so"
modparam("auth_db", "calculate_ha1", yes)
modparam("auth_db", "password_column", "password")
modparam("auth_db", "db_url",
"mysql://opensips:opensipsrw@localhost/opensips") # CUSTOMIZE ME
modparam("auth_db", "load_credentials", "")

#### DIALOG module
loadmodule "dialog.so"
modparam("dialog", "dlg_match_mode", 1)
modparam("dialog", "default_timeout", 21600)  # 6 hours timeout
modparam("dialog", "db_mode", 2)
modparam("dialog", "db_url",
"mysql://opensips:opensipsrw@localhost/opensips") # CUSTOMIZE ME

####  NAT modules
loadmodule "nathelper.so"
modparam("nathelper", "natping_interval", 10)
modparam("nathelper", "ping_nated_only", 1)
modparam("nathelper", "received_avp", "$avp(received_nh)")

#loadmodule "rtpproxy.so"
#modparam("rtpproxy", "rtpproxy_sock", "udp:localhost:12221") # CUSTOMIZE ME

loadmodule "mediaproxy.so"
modparam("mediaproxy", "mediaproxy_socket", "/var/run/mediaproxy/dispatcher.sock")
#modparam("mediaproxy", "mediaproxy_timeout", 500)
modparam("mediaproxy", "media_relay_avp", "$avp(media_relay)")
modparam("mediaproxy", "signaling_ip_avp", "$avp(nat_ip)")
#modparam("mediaproxy", "ice_candidate", "low-priority")
#modparam("mediaproxy", "ice_candidate_avp", "$avp(ice_candidate)")

####### Routing Logic ########

# main request routing logic

route{
force_rport();
if (nat_uac_test("23")) {
if (is_method("REGISTER")) {
fix_nated_register();
setbflag(10);
} else {
fix_nated_contact();
setflag(10);
}
}

if (!mf_process_maxfwd_header("10")) {
sl_send_reply("483","Too Many Hops");
exit;
}

if (has_totag()) {
# sequential request withing a dialog should
# take the path determined by record-routing
if (loose_route()) {

# validate the sequential request against dialog
if ( $DLG_status!=NULL && !validate_dialog() ) {
xlog("In-Dialog $rm from $si (callid=$ci) is not valid according to dialog\n");
## exit;
}

if (is_method("BYE")) {
setflag(1); # do accounting …
setflag(3); # … even if the transaction fails
} else if (is_method("INVITE")) {
# even if in most of the cases is useless, do RR for
# re-INVITEs alos, as some buggy clients do change route set
# during the dialog.
record_route();
}

if (check_route_param("nat=yes"))
setflag(10);

# route it out to whatever destination was set by loose_route()
# in $du (destination URI).
route(1);
} else {

if ( is_method("ACK") ) {
if ( t_check_trans() ) {
# non loose-route, but stateful ACK; must be an ACK after
# a 487 or e.g. 404 from upstream server
t_relay();
exit;
} else {
# ACK without matching transaction ->
# ignore and discard
exit;
}
}
sl_send_reply("404","Not here");
}
exit;
}

# CANCEL processing
if (is_method("CANCEL"))
{
if (t_check_trans())
t_relay();
exit;
}

t_check_trans();

if ( !(is_method("REGISTER")  ) ) {

if (from_uri==myself)

{

# authenticate if from local subscriber
# authenticate all initial non-REGISTER request that pretend to be
# generated by local subscriber (domain from FROM URI is local)
if (!proxy_authorize("", "subscriber")) {
proxy_challenge("", "0");
exit;
}
if (!db_check_from()) {
sl_send_reply("403","Forbidden auth ID");
exit;
}

consume_credentials();
# caller authenticated

} else {
# if caller is not local, then called number must be local

if (!uri==myself) {
send_reply("403","Rely forbidden");
exit;
}
}

}

# preloaded route checking
if (loose_route()) {
xlog("L_ERR",
"Attempt to route with preloaded Route's ");
if (!is_method("ACK"))
sl_send_reply("403","Preload Route denied");
exit;
}

# record routing
if (!is_method("REGISTER|MESSAGE"))
record_route();

# account only INVITEs
if (is_method("INVITE")) {

# create dialog with timeout
if ( !create_dialog("B") ) {
send_reply("500","Internal Server Error");
exit;
}

setflag(1); # do accounting
}

if (!uri==myself) {
append_hf("P-hint: outbound\r\n");

route(1);
}

# requests for my domain

if (is_method("PUBLISH|SUBSCRIBE"))
{
sl_send_reply("503", "Service Unavailable");
exit;
}

if (is_method("REGISTER"))
{

# authenticate the REGISTER requests
if (!www_authorize("", "subscriber"))
{
www_challenge("", "0");
exit;
}

if (!db_check_to())
{
sl_send_reply("403","Forbidden auth ID");
exit;
}

if ( proto==TCP ||  0 ) setflag(7);

if (!save("location"))
sl_reply_error();

exit;
}

if ($rU==NULL) {
# request with no Username in RURI
sl_send_reply("484","Address Incomplete");
exit;
}

# do lookup with method filtering
if (!lookup("location","m")) {
if (!db_does_uri_exist()) {
send_reply("420","Bad Extension");
exit;
}

t_newtran();
t_reply("404", "Not Found");
exit;
}

if (isbflagset(10)) setflag(10);

# when routing via usrloc, log the missed calls also
setflag(2);
route(1);
}

route {
# for INVITEs enable some additional helper routes
if (is_method("INVITE")) {

#engage_media_proxy();

if (isflagset(10)) {
use_media_proxy();
}

t_on_branch("2");
t_on_reply("2");
t_on_failure("1");
}

if (isflagset(10)) {
add_rr_param(";nat=yes");
}

if (!t_relay()) {
send_reply("500","Internal Error");
};
exit;
}

branch_route {
xlog("new branch at $ru\n");
}

onreply_route {
if (nat_uac_test("1"))
fix_nated_contact();
if ( isflagset(10) )
end_media_session();
xlog("incoming reply\n");
}

failure_route {
if (t_was_cancelled()) {
exit;
}

# uncomment the following lines if you want to block client
# redirect based on 3xx replies.
##if (t_check_status("3")) {
##t_reply("404","Not found");
## exit;
##}

}

local_route {
if (is_method("BYE") && $DLG_dir=="UPSTREAM") {

acc_db_request("200 Dialog Timeout", "acc");

}
}

sip client  is doubango, and run behind nat.

sip client can't communicate to other.

what's the problem with the config file?

How to config?