diff --git a/src/src/main/java/com/my/graphiteDigesterBg/diframe/connection/DiConWebsocket.java b/src/src/main/java/com/my/graphiteDigesterBg/diframe/connection/DiConWebsocket.java
index 250b865..2f4bbc7 100644
--- a/src/src/main/java/com/my/graphiteDigesterBg/diframe/connection/DiConWebsocket.java
+++ b/src/src/main/java/com/my/graphiteDigesterBg/diframe/connection/DiConWebsocket.java
@@ -12,10 +12,8 @@ import java.nio.ByteOrder;
 import java.nio.CharBuffer;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Timer;
-import java.util.TimerTask;
+import java.util.*;
+
 public class DiConWebsocket implements DiDeviceConnection {
     // logger
     public static final Logger LOG = LoggerFactory.getLogger(DiConWebsocket.class);
@@ -28,7 +26,7 @@ public class DiConWebsocket implements DiDeviceConnection {
 
     // constructor
     public DiConWebsocket() {
-        this.requests = new ArrayList<>();
+        this.requests = new Vector<>();
     }
 
     @Override
@@ -54,7 +52,7 @@ public class DiConWebsocket implements DiDeviceConnection {
     }
 
     @Override
-    public void call(DiCommandRequest request) {
+    synchronized public void call(DiCommandRequest request) {
         this.requests.add(request);
 
         // build cmd from request.parameter
@@ -72,6 +70,7 @@ public class DiConWebsocket implements DiDeviceConnection {
             } catch (InterruptedException e) {
                 throw new RuntimeException(e);
             }
+            this.requests.remove(request);
         }
         LOG.info("Command <= {}", DiByteBuffer.toHex(request.response));
     }