diff --git a/config.js b/config.js
index 00696a7..c1e78bc 100644
--- a/config.js
+++ b/config.js
@@ -27,8 +27,8 @@ module.exports = {
             "-PixelStreamingWebRTCDisableAudioSync",
             "-PixelStreamingHideCursor=true",
             "-PixelStreamingKeyFilter=ESC, CTRL",
-            //"-SimulcastParameters=1.0,5000000,100000000,2.0,1000000,5000000,3.0,500000,2500000",
-            //"-PixelStreamingHudStats=true" // usefull for debug
+            "-SimulcastParameters=1.0,5000000,100000000,2.0,1000000,5000000,3.0,500000,2500000",
+            "-PixelStreamingHudStats=true" // usefull for debug
         ]
     }
 }
\ No newline at end of file
diff --git a/src/controller/session.js b/src/controller/session.js
index a50565f..14a0974 100644
--- a/src/controller/session.js
+++ b/src/controller/session.js
@@ -19,7 +19,7 @@ const run_session = async (req, res, next) => {
 
     let webrtc_port = await get_webrtc_port()
     let app_port = await get_app_port()
-    let sfu_port = 8889//await get_sfu_port()
+    let sfu_port = await get_sfu_port()
 
     if (!app_port) {
         next(new server_error('all app ports busy'))
@@ -27,11 +27,10 @@ const run_session = async (req, res, next) => {
     } else if (!webrtc_port) {
         next(new server_error('all webrtc ports busy'))
         return
-    } 
-    // else if (!sfu_port) {
-    //     next(new server_error('all sfu ports busy'))
-    //     return
-    // }
+    } else if (!sfu_port) {
+        next(new server_error('all sfu ports busy'))
+        return
+    }
 
     let app_pid = await run_app(app_path, app_port)
     if (!app_pid) {
@@ -48,13 +47,13 @@ const run_session = async (req, res, next) => {
         return
     }
 
-    let sfu_pid = null //await run_sfu(sfu_port)
-    // if (!sfu_pid) {
-    //     kill_proc(app_pid)
-    //     kill_proc(webrtc_pid)
-    //     next(new server_error('can not run sfu'))
-    //     return
-    // }
+    let sfu_pid = await run_sfu(sfu_port)
+    if (!sfu_pid) {
+        kill_proc(app_pid)
+        kill_proc(webrtc_pid)
+        next(new server_error('can not run sfu'))
+        return
+    }
 
 
     let add_runnning_session_result = await database.add_running_session(session_id, title, app_pid, webrtc_pid, sfu_pid, app_port, webrtc_port, sfu_port)
diff --git a/src/modules/session_observer.js b/src/modules/session_observer.js
index 023489c..0e2d2c7 100644
--- a/src/modules/session_observer.js
+++ b/src/modules/session_observer.js
@@ -8,11 +8,23 @@ const {free_app_port, free_webrtc_port, free_sfu_port} = require('./port_alloc')
 const observer_timeout = 100
 let pending_list = new wait_list([])
 
-const start_observer = () => {
-    check()
+let can_check = true
+const block_time = 30000
+
+const start_observer = async () => {
+    if (can_check) {
+        check()
+    }
     setTimeout(() => start_observer(), observer_timeout)
 }
 
+const block_for = (time) => {
+    can_check = false
+    setTimeout(() => {
+        can_check = true
+    }, time)
+}
+
 // check sessions in parallel
 const check_sessions = async (sessions) => {
 
@@ -47,6 +59,7 @@ const check_sessions = async (sessions) => {
                 await database.remove_running_session(session.session_id)
             } else {
                 console.error('can not connect to coordinator')
+                block_for(block_time)
             }
             pending_list.remove(session.session_id)
         }
@@ -57,10 +70,11 @@ const check = async () => {
     let sessions = await database.get_running_sessions()
 
     if (!sessions) {
+        block_for(block_time)
         return
     }
 
-    check_sessions(sessions)
+    await check_sessions(sessions)
 }
 
 module.exports = {