dispatcher extensions

- distribute also Register and Subscribes to groups 20 and 30
  respectively
- for Invites introduce a backup group 2 to be used in case in group 1
  there are less than 3 available gateways

kamailio/dispatcher-role.cfg

@@ -40,12 +40,49 @@ route[DISPATCHER_FIND_ROUTES]
         return;
     }
 
-    if (!ds_select_dst("1", "0")) {
-        xlog("L_ERR", "$ci|end|no servers avaliable");
+    if (is_method("SUBSCRIBE")) {
+        $var(ds_group) = 20;
+    } else
+    if (is_method("REGISTER")) {
+        $var(ds_group) = 30;
+    } else {
+        $var(ds_group) = 1;
+    }
+
+    if (!ds_select_dst("$var(ds_group)", "0")) {
+        xlog("L_ERR", "$ci|end|no servers avaliable in group $var(ds_group)");
+
+        # if we selected from group 1, try again in group 2
+        if ($var(ds_group) == 1 ) {
+
+                if (!ds_select_dst("2", "0")) {
+                    xlog("L_ERR", "$ci|end|no servers avaliable in group 2");
+                    sl_send_reply("480", "All servers busy");
+                    exit;
+                }
+
+        } else {
+
+            sl_send_reply("480", "All servers busy");
+            exit;
 
-        sl_send_reply("480", "All servers busy");
+        }
+    } else {
+
+        # if we selected from group 1 and there are less than 3 available servers, choose from group 2
+        if ($var(ds_group) == 1 && $var(ds_cnt)< 3) {
+
+            # clear $avp(ds_dst) and search in group 2
+            $(avp(ds_dst)[*]) = $null;
+
+            if (!ds_select_dst("2", "0")) {
+                xlog("L_ERR", "$ci|end|no servers avaliable in group 2");
+                sl_send_reply("480", "All servers busy");
+                exit;
+            }
+
+        }
 
-        exit;
     }
 
     $var(contact_uri) = $(ct{tobody.user}) + "@" + $(ct{tobody.host});