diff --git a/xos/synchronizer/__init__.py b/xos/synchronizer/__init__.py
index 8bbb6fa..42722a8 100644
--- a/xos/synchronizer/__init__.py
+++ b/xos/synchronizer/__init__.py
@@ -11,4 +11,4 @@
 # distributed under the License is distributed on an "AS IS" BASIS,
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
-# limitations under the License.
\ No newline at end of file
+# limitations under the License.
diff --git a/xos/synchronizer/event_steps/dhcp_event.py b/xos/synchronizer/event_steps/dhcp_event.py
index 8b3ea8d..92828f6 100644
--- a/xos/synchronizer/event_steps/dhcp_event.py
+++ b/xos/synchronizer/event_steps/dhcp_event.py
@@ -14,12 +14,9 @@
 # limitations under the License.
 
 import json
-import time
-import os
-import sys
 from xossynchronizer.event_steps.eventstep import EventStep
+from helpers import TtHelpers
 
-from ..helpers import TtHelpers
 
 class SubscriberDhcpEventStep(EventStep):
     topics = ["dhcp.events"]
@@ -30,18 +27,11 @@
 
     def process_event(self, event):
         value = json.loads(event.value)
+        self.log.info("dhcp.events: Got event for subscriber", event_value=value)
 
-        onu_sn = TtHelpers.get_onu_sn(self.model_accessor, self.log, value)
-        si = TtHelpers.get_si_by_sn(self.model_accessor, self.log, onu_sn)
-
-        if not si:
-            self.log.exception("dhcp.events: Cannot find tt-workflow-driver service instance for this event", kafka_event=value)
-            raise Exception("dhcp.events: Cannot find tt-workflow-driver service instance for this event")
-
-        self.log.info("dhcp.events: Got event for subscriber", event_value=value, onu_sn=onu_sn, si=si)
-
+        si = TtHelpers.find_or_create_tt_si(self.model_accessor, self.log, value)
+        self.log.debug("dhcp.events: Updating service instance", si=si)
         si.dhcp_state = value["messageType"]
         si.ip_address = value["ipAddress"]
         si.mac_address = value["macAddress"]
-
         si.save_changed_fields(always_update_timestamp=True)
diff --git a/xos/synchronizer/event_steps/onu_event.py b/xos/synchronizer/event_steps/onu_event.py
index 3a18c26..8d64254 100644
--- a/xos/synchronizer/event_steps/onu_event.py
+++ b/xos/synchronizer/event_steps/onu_event.py
@@ -16,6 +16,8 @@
 
 import json
 from xossynchronizer.event_steps.eventstep import EventStep
+from helpers import TtHelpers
+
 
 class ONUEventStep(EventStep):
     topics = ["onu.events"]
@@ -26,31 +28,16 @@
     def __init__(self, *args, **kwargs):
         super(ONUEventStep, self).__init__(*args, **kwargs)
 
-    def get_tt_si(self, event):
-        try:
-            tt_si = self.model_accessor.TtWorkflowDriverServiceInstance.objects.get(serial_number=event["serialNumber"])
-            tt_si.no_sync = False;
-            tt_si.uni_port_id = long(event["portNumber"])
-            tt_si.of_dpid = event["deviceId"]
-            self.log.debug("onu.events: Found existing TtWorkflowDriverServiceInstance", si=tt_si)
-        except IndexError:
-            # create an TtWorkflowDriverServiceInstance, the validation will be triggered in the corresponding sync step
-            tt_si = self.model_accessor.TtWorkflowDriverServiceInstance(
-                serial_number=event["serialNumber"],
-                of_dpid=event["deviceId"],
-                uni_port_id=long(event["portNumber"]),
-                owner=self.model_accessor.TtWorkflowDriverService.objects.first() # we assume there is only one TtWorkflowDriverService
-            )
-            self.log.debug("onu.events: Created new TtWorkflowDriverServiceInstance", si=tt_si)
-        return tt_si
-
     def process_event(self, event):
         value = json.loads(event.value)
         self.log.info("onu.events: received event", value=value)
 
         if value["status"] == "activated":
             self.log.info("onu.events: activated onu", value=value)
-            tt_si = self.get_tt_si(value)
+            tt_si = TtHelpers.find_or_create_tt_si(self.model_accessor, self.log, value)
+            tt_si.no_sync = False
+            tt_si.uni_port_id = long(value["portNumber"])
+            tt_si.of_dpid = value["deviceId"]
             tt_si.onu_state = "ENABLED"
             tt_si.save_changed_fields(always_update_timestamp=True)
         elif value["status"] == "disabled":
diff --git a/xos/synchronizer/event_steps/test_dhcp_event.py b/xos/synchronizer/event_steps/test_dhcp_event.py
index d7934da..d51ee7a 100644
--- a/xos/synchronizer/event_steps/test_dhcp_event.py
+++ b/xos/synchronizer/event_steps/test_dhcp_event.py
@@ -13,12 +13,14 @@
 # limitations under the License.
 
 import unittest
-from mock import patch, call, Mock, PropertyMock
+from mock import patch, Mock
 import json
 
-import os, sys
+import os
+import sys
 
-test_path=os.path.abspath(os.path.dirname(os.path.realpath(__file__)))
+test_path = os.path.abspath(os.path.dirname(os.path.realpath(__file__)))
+
 
 class TestSubscriberAuthEvent(unittest.TestCase):
 
@@ -42,7 +44,7 @@
 
         import xossynchronizer.modelaccessor
         import mock_modelaccessor
-        reload(mock_modelaccessor) # in case nose2 loaded it in a previous test
+        reload(mock_modelaccessor)  # in case nose2 loaded it in a previous test
         reload(xossynchronizer.modelaccessor)      # in case nose2 loaded it in a previous test
 
         from xossynchronizer.modelaccessor import model_accessor
@@ -74,28 +76,22 @@
         self.si.serial_number = "BRCM1234"
         self.si.save = Mock()
 
-
     def tearDown(self):
         sys.path = self.sys_path_save
 
     def test_dhcp_subscriber(self):
 
         self.event.value = json.dumps({
-            "deviceId" : "of:0000000000000001",
-            "portNumber" : "1",
-            "macAddress" : self.mac_address,
-            "ipAddress" : self.ip_address,
-            "messageType": "DHCPREQUEST"
+            "deviceId": "of:0000000000000001",
+            "portNumber": "1",
+            "macAddress": self.mac_address,
+            "ipAddress": self.ip_address,
+            "messageType": "DHCPREQUEST",
+            'serialNumber': "BRCM1234",
         })
 
-        with patch.object(VOLTService.objects, "get_items") as volt_service_mock, \
-            patch.object(TtWorkflowDriverServiceInstance.objects, "get_items") as si_mock, \
-            patch.object(self.volt, "get_onu_sn_from_openflow") as get_onu_sn:
+        with patch.object(TtWorkflowDriverServiceInstance.objects, "get_items") as si_mock:
 
-            self.assertTrue(VOLTService.objects.first() is not None)
-
-            volt_service_mock.return_value = [self.volt]
-            get_onu_sn.return_value = "BRCM1234"
             si_mock.return_value = [self.si]
 
             self.event_step.process_event(self.event)
@@ -105,6 +101,7 @@
             self.assertEqual(self.si.mac_address, self.mac_address)
             self.assertEqual(self.si.ip_address, self.ip_address)
 
+
 if __name__ == '__main__':
-    sys.path.append("..") # for import of helpers.py
-    unittest.main()
\ No newline at end of file
+    sys.path.append(os.path.join(os.path.dirname(os.path.realpath(__file__)), ".."))  # for import of helpers.py
+    unittest.main()
diff --git a/xos/synchronizer/event_steps/test_onu_events.py b/xos/synchronizer/event_steps/test_onu_events.py
index 0bd1c31..c11812f 100644
--- a/xos/synchronizer/event_steps/test_onu_events.py
+++ b/xos/synchronizer/event_steps/test_onu_events.py
@@ -131,5 +131,5 @@
             
 
 if __name__ == '__main__':
-    sys.path.append("..")  # for import of helpers.py
+    sys.path.append(os.path.join(os.path.dirname(os.path.realpath(__file__)), ".."))  # for import of helpers.py
     unittest.main()
diff --git a/xos/synchronizer/helpers.py b/xos/synchronizer/helpers.py
index e67890a..a300892 100644
--- a/xos/synchronizer/helpers.py
+++ b/xos/synchronizer/helpers.py
@@ -58,19 +58,21 @@
         return [True, "ONU has been validated"]
 
     @staticmethod
-    def get_onu_sn(model_accessor, log, event):
-        olt_service = model_accessor.VOLTService.objects.first()
-        onu_sn = olt_service.get_onu_sn_from_openflow(event["deviceId"], event["portNumber"])
-        if not onu_sn or onu_sn is None:
-            log.exception("Cannot find onu serial number for this event", kafka_event=event)
-            raise Exception("Cannot find onu serial number for this event")
-
-        return onu_sn
-
-    @staticmethod
-    def get_si_by_sn(model_accessor, log, serial_number):
+    def find_or_create_tt_si(model_accessor, log, event):
         try:
-            return model_accessor.TtWorkflowDriverServiceInstance.objects.get(serial_number=serial_number)
+            tt_si = model_accessor.TtWorkflowDriverServiceInstance.objects.get(
+                serial_number=event["serialNumber"]
+            )
+            log.debug("TtHelpers: Found existing TtWorkflowDriverServiceInstance", si=tt_si)
         except IndexError:
-            log.exception("Cannot find tt-workflow-driver service instance for this serial number", serial_number=serial_number)
-            raise Exception("Cannot find tt-workflow-driver service instance for this serial number %s", serial_number)
\ No newline at end of file
+            # create a TtWorkflowDriverServiceInstance, the validation will be
+            # triggered in the corresponding sync step
+            tt_si = model_accessor.TtWorkflowDriverServiceInstance(
+                serial_number=event["serialNumber"],
+                of_dpid=event["deviceId"],
+                uni_port_id=long(event["portNumber"]),
+                # we assume there is only one TtWorkflowDriverService
+                owner=model_accessor.TtWorkflowDriverService.objects.first()
+            )
+            log.debug("TtHelpers: Created new TtWorkflowDriverServiceInstance", si=tt_si)
+        return tt_si
diff --git a/xos/synchronizer/tt-workflow-driver-synchronizer.py b/xos/synchronizer/tt-workflow-driver-synchronizer.py
index 9b420e7..eb378ad 100644
--- a/xos/synchronizer/tt-workflow-driver-synchronizer.py
+++ b/xos/synchronizer/tt-workflow-driver-synchronizer.py
@@ -31,4 +31,4 @@
 else:
     Config.init(base_config_file, 'synchronizer-config-schema.yaml')
 
-Synchronizer().run()
\ No newline at end of file
+Synchronizer().run()