diff --git a/server/abstractport.cpp b/server/abstractport.cpp
index b43a312..1764d52 100644
--- a/server/abstractport.cpp
+++ b/server/abstractport.cpp
@@ -65,6 +65,28 @@ void AbstractPort::init()
 {
 }    
 
+/*! Can we modify Port with these params? Should modify cause port dirty? */
+bool AbstractPort::canModify(const OstProto::Port &port, bool *dirty)
+{
+    bool allow = true;
+
+    *dirty = false;
+
+    if (port.has_transmit_mode()
+            && (port.transmit_mode() != data_.transmit_mode())) {
+        *dirty = true;
+        allow = !isTransmitOn();
+    }
+
+    if (port.has_streams_type()
+            && (port.streams_type() != data_.streams_type())) {
+        *dirty = true;
+        allow = !isTransmitOn();
+    }
+
+    return allow;
+}
+
 bool AbstractPort::modify(const OstProto::Port &port)
 {
     bool ret = true;
diff --git a/server/abstractport.h b/server/abstractport.h
index 426c475..da5c70e 100644
--- a/server/abstractport.h
+++ b/server/abstractport.h
@@ -87,6 +87,7 @@ public:
     const char* name() { return data_.name().c_str(); }
     void protoDataCopyInto(OstProto::Port *port) { port->CopyFrom(data_); }
 
+    bool canModify(const OstProto::Port &port, bool *dirty);
     bool modify(const OstProto::Port &port);
 
     virtual OstProto::LinkState linkState() { return linkState_; }
diff --git a/server/myservice.cpp b/server/myservice.cpp
index 88c627b..334853f 100644
--- a/server/myservice.cpp
+++ b/server/myservice.cpp
@@ -133,13 +133,20 @@ void MyService::modifyPort(::google::protobuf::RpcController* /*controller*/,
         id = port.port_id().id();
         if (id < portInfo.size())
         {
-            // FIXME: return error for any change in transmitMode/streamsType
-            // while transmit is on
+            bool dirty;
+
+            if (!portInfo[id]->canModify(port, &dirty)) {
+                qDebug("Port %d cannot be modified - stop tx and retry", id);
+                continue;        //! \todo(LOW): Partial status of RPC
+            }
 
             portLock[id]->lockForWrite();
             portInfo[id]->modify(port);
+            if (dirty)
+                portInfo[id]->updatePacketList();
             portLock[id]->unlock();
 
+
             notif->mutable_port_id_list()->add_port_id()->set_id(id);
         }
     }