kamailio.cfg: updated cfg with sample PSTN gw routing

- defined within WITH_PSTN
- calls to numbers starting with + or 00 are sent to PSTN GW
- use of custome cfg parameter to define GW IP
- remove preloaded Route headers for initial requests

etc/kamailio.cfg

@@ -38,6 +38,11 @@
 #     - start RTPProxy:
 #        rtpproxy -l _your_public_ip_ -s udp:localhost:7722
 #
+# *** To enable PSTN gateway routing execute:
+#     - define WITH_PSTN
+#     - set the value of pstn.gw_ip
+#     - check route[PSTN] for regexp routing condition
+#
 # *** To enhance accounting execute:
 #     - enable mysql
 #     - define WITH_ACCDB
@@ -88,6 +93,26 @@ port=5060
 #listen=udp:10.0.0.10:5060
 
 
+####### Custom Parameters #########
+
+# These parameters can be modified runtime via RPC interface
+# - see the documentation of 'cfg_rpc' module.
+#
+# Format: group.id = value 'desc' description
+# Access: $sel(cfg_get.group.id) or @cfg_get.group.id
+#
+
+#!ifdef WITH_PSTN
+# PSTN GW Routing
+#
+# - pstn.gw_ip: valid IP or hostname as string value, example:
+# pstn.gw_ip = "10.0.0.101" desc "My PSTN GW Address"
+#
+# - by default is empty to avoid misrouting
+pstn.gw_ip = "" desc "PSTN GW Address"
+#!endif
+
+
 ####### Modules Section ########
 
 #set module path
@@ -316,6 +341,8 @@ route{
 	route(AUTH);
 
 	# record routing for dialog forming requests (in case they are routed)
+	# - remove preloaded route headers
+	remove_hf("Route");
 	if (is_method("INVITE|SUBSCRIBE"))
 		record_route();
 
@@ -356,6 +383,8 @@ route{
 		exit;
 	}
 
+	route(PSTN);
+
 	# apply DB based aliases (uncomment to enable)
 	##alias_db_lookup("dbaliases");
 
@@ -511,6 +540,36 @@ route[RTPPROXY] {
 	return;
 }
 
+# PSTN GW routing
+route[PSTN] {
+#!ifdef WITH_PSTN
+	# check if PSTN GW IP is defined
+	if (strempty($sel(cfg_get.pstn.gw_ip))) {
+		xlog("SCRIPT: PSTN rotuing enabled but pstn.gw_ip not defined\n");
+		return;
+	}
+
+	# route to PSTN dialed numbers starting with '+' or '00'
+	#     (international format)
+	# - update the condition to match your dialing rules for PSTN routing
+	if(!($rU=~"^(\+|00)[1-9][0-9]{3,20}$"))
+		return;
+
+	# only local users allowed to call
+	if(from_uri!=myself) {
+		sl_send_reply("403", "Not Allowed");
+		exit;
+	}
+
+	$ru = "sip:" + $rU + "@" + $sel(cfg_get.pstn.gw_ip);
+
+	route(RELAY);
+	exit;
+#!endif
+
+	return;
+}
+
 # Sample branch router
 branch_route[BRANCH_ONE] {
 	xdbg("new branch at $ru\n");