diff --git a/kamailio/default.cfg b/kamailio/default.cfg
index 0039932..abaff4b 100644
--- a/kamailio/default.cfg
+++ b/kamailio/default.cfg
@@ -710,7 +710,11 @@ route[INTERNAL_TO_EXTERNAL_RELAY]
 
     t_on_reply("EXTERNAL_REPLY");
 
-    t_set_fr(0, $sel(cfg_get.kazoo.to_external_no_response_initial_timer));
+    if($sel(cfg_get.kazoo.use_progressive_timers) == 1) {
+        t_set_fr(0, $sel(cfg_get.kazoo.to_external_no_response_initial_timer));
+    } else {
+        t_set_fr(0, $sel(cfg_get.kazoo.to_external_no_response_timer));
+    }
 
     t_relay();
 }
@@ -727,7 +731,11 @@ route[EXTERNAL_TO_INTERNAL_RELAY]
     t_on_reply("INTERNAL_REPLY");
     t_on_failure("INTERNAL_FAULT");
 
-    t_set_fr(0, $sel(cfg_get.kazoo.to_internal_no_response_initial_timer));
+    if($sel(cfg_get.kazoo.use_progressive_timers) == 1) {
+        t_set_fr(0, $sel(cfg_get.kazoo.to_internal_no_response_initial_timer));
+    } else {
+        t_set_fr(0, $sel(cfg_get.kazoo.to_internal_no_response_timer));
+    }
 
     #!ifdef WITH_INTERNAL_LISTENER
     xlog("L_DEBUG", "$ci|route|routing to internal thru PORT_PROTO_INTERNAL_LISTENER\n");
@@ -742,9 +750,13 @@ onreply_route[EXTERNAL_REPLY]
     xlog("L_INFO", "$ci|log|external reply $T_reply_code $T_reply_reason\n");
 
     if($rs == 100) {
-        t_set_fr(0, $sel(cfg_get.kazoo.to_external_no_response_100_timer));
+        if($sel(cfg_get.kazoo.use_progressive_timers) == 1) {
+            t_set_fr(0, $sel(cfg_get.kazoo.to_external_no_response_100_timer));
+        }
     } else if(status=~"[1][8][0-9]") {
-        t_set_fr(0, $sel(cfg_get.kazoo.to_external_no_response_18X_timer));
+        if($sel(cfg_get.kazoo.use_progressive_timers) == 1) {
+            t_set_fr(0, $sel(cfg_get.kazoo.to_external_no_response_18X_timer));
+        }
     }
 
     #!ifdef NAT_TRAVERSAL_ROLE
@@ -774,13 +786,13 @@ onreply_route[INTERNAL_REPLY]
     }
 
     if($rs == 100) {
-        t_set_fr(0, $sel(cfg_get.kazoo.to_internal_no_response_100_timer));
+        if($sel(cfg_get.kazoo.use_progressive_timers) == 1) {
+            t_set_fr(0, $sel(cfg_get.kazoo.to_internal_no_response_100_timer));
+        }
     } else if(status=~"[1][8][0-9]") {
-        t_set_fr(0, $sel(cfg_get.kazoo.to_internal_no_response_18X_timer));
-    }
-
-    if($rs == 100) {
-        t_set_fr(0, $sel(cfg_get.kazoo.to_internal_no_response_100_timer));
+        if($sel(cfg_get.kazoo.use_progressive_timers) == 1) {
+            t_set_fr(0, $sel(cfg_get.kazoo.to_internal_no_response_18X_timer));
+        }
     }
 
     #!ifdef NAT_TRAVERSAL_ROLE
diff --git a/kamailio/defs.cfg b/kamailio/defs.cfg
index 8f2f6ca..8d0fa65 100644
--- a/kamailio/defs.cfg
+++ b/kamailio/defs.cfg
@@ -7,8 +7,13 @@
 
 #!substdef "!MAJOR!$(version(num){re.subst,/^(([^\.])*\.([^\.])*)\..*/\1/})!g"
 
-#!trydef EXTERNAL_TO_INTERNAL_NO_RESPONSE_INITIAL_TIMER 2000
-#!trydef INTERNAL_TO_EXTERNAL_NO_RESPONSE_INITIAL_TIMER 2500
+#!trydef EXTERNAL_TO_INTERNAL_NO_RESPONSE_TIMER 3500
+#!trydef INTERNAL_TO_EXTERNAL_NO_RESPONSE_TIMER 3500
+
+#!trydef USE_PROGRESSIVE_TIMERS 0
+
+#!trydef EXTERNAL_TO_INTERNAL_NO_RESPONSE_INITIAL_TIMER 1500
+#!trydef INTERNAL_TO_EXTERNAL_NO_RESPONSE_INITIAL_TIMER 1500
 
 #!trydef EXTERNAL_TO_INTERNAL_NO_RESPONSE_100_TIMER 4500
 #!trydef INTERNAL_TO_EXTERNAL_NO_RESPONSE_100_TIMER 4500
@@ -16,6 +21,11 @@
 #!trydef EXTERNAL_TO_INTERNAL_NO_RESPONSE_18X_TIMER 45000
 #!trydef INTERNAL_TO_EXTERNAL_NO_RESPONSE_18X_TIMER 45000
 
+kazoo.to_internal_no_response_timer = EXTERNAL_TO_INTERNAL_NO_RESPONSE_TIMER descr "external to internal no response timer"
+kazoo.to_external_no_response_timer = INTERNAL_TO_EXTERNAL_NO_RESPONSE_TIMER descr "internal to external no response timer"
+
+kazoo.use_progressive_timers = USE_PROGRESSIVE_TIMERS descr "use progressive timers"
+
 kazoo.to_internal_no_response_initial_timer = EXTERNAL_TO_INTERNAL_NO_RESPONSE_INITIAL_TIMER descr "external to internal initial no response timer"
 kazoo.to_external_no_response_initial_timer = INTERNAL_TO_EXTERNAL_NO_RESPONSE_INITIAL_TIMER descr "internal to external initial no response timer"
 kazoo.to_internal_no_response_100_timer = EXTERNAL_TO_INTERNAL_NO_RESPONSE_100_TIMER descr "external to internal no response timer after 100"