diff --git a/xos/synchronizer/helpers.py b/xos/synchronizer/helpers.py
new file mode 100644
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+++ b/xos/synchronizer/helpers.py
@@ -0,0 +1,59 @@
+# Copyright 2017-present Open Networking Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# 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.
+
+from synchronizers.new_base.syncstep import DeferredException
+from synchronizers.new_base.modelaccessor import AttWorkflowDriverWhiteListEntry, ONUDevice, model_accessor
+
+from xosconfig import Config
+from multistructlog import create_logger
+
+log = create_logger(Config().get('logging'))
+
+class AttHelpers():
+
+    @staticmethod
+    def validate_onu(att_si):
+        """
+        This method validate an ONU against the whitelist and set the appropriate state.
+        It's expected that the deferred exception is managed in the caller method,
+        for example a model_policy or a sync_step.
+
+        :param att_si: AttWorkflowDriverServiceInstance
+        :return: [boolean, string]
+        """
+
+        oss_service = att_si.owner.leaf_model
+
+        # See if there is a matching entry in the whitelist.
+        matching_entries = AttWorkflowDriverWhiteListEntry.objects.filter(
+            owner_id=oss_service.id,
+        )
+        matching_entries = [e for e in matching_entries if e.serial_number.lower() == att_si.serial_number.lower()]
+
+        if len(matching_entries) == 0:
+            log.warn("ONU not found in whitelist", object=str(att_si), serial_number=att_si.serial_number, **att_si.tologdict())
+            return [False, "ONU not found in whitelist"]
+
+        whitelisted = matching_entries[0]
+        try:
+            pon_port = ONUDevice.objects.get(serial_number=att_si.serial_number).pon_port
+        except IndexError:
+            raise DeferredException("ONU device %s is not know to XOS yet" % att_si.serial_number)
+
+        if pon_port.port_no != whitelisted.pon_port_id or att_si.of_dpid != whitelisted.device_id:
+            log.warn("ONU disable as location don't match", object=str(att_si), serial_number=att_si.serial_number,
+                     **att_si.tologdict())
+            return [False, "ONU activated in wrong location"]
+
+        return [True, "ONU has been validated"]
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