diff --git a/omci_messages.py b/omci_messages.py
new file mode 100644
index 0000000..90a0cea
--- /dev/null
+++ b/omci_messages.py
@@ -0,0 +1,300 @@
+#
+# Copyright 2017 the original author or authors.
+#
+# 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.
+#
+import structlog
+from enum import Enum
+from scapy.fields import ByteField, StrFixedLenField, ConditionalField, Field
+from scapy.fields import ShortField
+from scapy.packet import Packet
+
+from voltha.extensions.omci.omci_defs import AttributeAccess
+from voltha.extensions.omci.omci_entities import entity_id_to_class_map
+
+
+log = structlog.get_logger()
+
+
+class OmciData(Field):
+
+    __slots__ = Field.__slots__ + ['_entity_class']
+
+    def __init__(self, name, entity_class="entity_class"):
+        Field.__init__(self, name=name, default=None, fmt='s')
+        self._entity_class = entity_class
+
+    def addfield(self, pkt, s, val):
+        class_id = getattr(pkt, self._entity_class)
+        entity_class = entity_id_to_class_map.get(class_id)
+        for attribute in entity_class.attributes:
+            if AttributeAccess.SetByCreate not in attribute._access:
+                continue
+            if attribute._fld.name == 'managed_entity_id':
+                continue
+            fld = attribute._fld
+            s = fld.addfield(pkt, s, val.get(fld.name, fld.default))
+        return s
+
+    def getfield(self, pkt, s):
+        """Extract an internal value from a string"""
+        class_id = getattr(pkt, self._entity_class)
+        entity_class = entity_id_to_class_map.get(class_id)
+        data = {}
+        for attribute in entity_class.attributes:
+            if AttributeAccess.SetByCreate not in attribute._access:
+                continue
+            if attribute._fld.name == 'managed_entity_id':
+                continue
+            fld = attribute._fld
+            s, value = fld.getfield(pkt, s)
+            data[fld.name] = value
+        return s, data
+
+
+class OmciMaskedData(Field):
+
+    __slots__ = Field.__slots__ + ['_entity_class', '_attributes_mask']
+
+    def __init__(self, name, entity_class="entity_class",
+                 attributes_mask="attributes_mask"):
+        Field.__init__(self, name=name, default=None, fmt='s')
+        self._entity_class = entity_class
+        self._attributes_mask = attributes_mask
+
+    def addfield(self, pkt, s, val):
+        class_id = getattr(pkt, self._entity_class)
+        attribute_mask = getattr(pkt, self._attributes_mask)
+        entity_class = entity_id_to_class_map.get(class_id)
+        indices = entity_class.attribute_indices_from_mask(attribute_mask)
+        for index in indices:
+            fld = entity_class.attributes[index]._fld
+            s = fld.addfield(pkt, s, val[fld.name])
+        return s
+
+    def getfield(self, pkt, s):
+        """Extract an internal value from a string"""
+        class_id = getattr(pkt, self._entity_class)
+        attribute_mask = getattr(pkt, self._attributes_mask)
+        entity_class = entity_id_to_class_map[class_id]
+        indices = entity_class.attribute_indices_from_mask(attribute_mask)
+        data = {}
+        for index in indices:
+            try:
+                fld = entity_class.attributes[index]._fld
+            except IndexError, e:
+                log.error("Cannot decode attribute {} for entity class {}".format(
+                        index, entity_class))
+                continue
+            try:
+                s, value = fld.getfield(pkt, s)
+            except Exception, e:
+                raise
+            data[fld.name] = value
+        return  s, data
+
+
+class OmciMessage(Packet):
+    name = "OmciMessage"
+    message_id = None  # OMCI message_type value, filled by derived classes
+    fields_desc = []
+
+
+class OmciCreate(OmciMessage):
+    name = "OmciCreate"
+    message_id = 0x44
+    fields_desc = [
+        ShortField("entity_class", None),
+        ShortField("entity_id", 0),
+        OmciData("data")
+    ]
+
+
+class OmciCreateResponse(OmciMessage):
+    name = "OmciCreateResponse"
+    message_id = 0x24
+    fields_desc = [
+        ShortField("entity_class", None),
+        ShortField("entity_id", None),
+        ByteField("success_code", 0),
+        ShortField("parameter_error_attributes_mask", None),
+    ]
+
+
+class OmciDelete(OmciMessage):
+    name = "OmciDelete"
+    message_id = 0x46
+    fields_desc = [
+        ShortField("entity_class", None),
+        ShortField("entity_id", None),
+    ]
+
+
+class OmciDeleteResponse(OmciMessage):
+    name = "OmciDeleteResponse"
+    message_id = 0x26
+    fields_desc = [
+        ShortField("entity_class", None),
+        ShortField("entity_id", None),
+        ByteField("success_code", 0),
+    ]
+
+
+class OmciSet(OmciMessage):
+    name = "OmciSet"
+    message_id = 0x48
+    fields_desc = [
+        ShortField("entity_class", None),
+        ShortField("entity_id", 0),
+        ShortField("attributes_mask", None),
+        OmciMaskedData("data")
+    ]
+
+
+class OmciSetResponse(OmciMessage):
+    name = "OmciSetResponse"
+    message_id = 0x28
+    fields_desc = [
+        ShortField("entity_class", None),
+        ShortField("entity_id", None),
+        ByteField("success_code", 0),
+        ShortField("unsupported_attributes_mask", None),
+        ShortField("failed_attributes_mask", None),
+    ]
+
+
+class OmciGet(OmciMessage):
+    name = "OmciGet"
+    message_id = 0x49
+    fields_desc = [
+        ShortField("entity_class", None),
+        ShortField("entity_id", 0),
+        ShortField("attributes_mask", None)
+    ]
+
+
+class OmciGetResponse(OmciMessage):
+    name = "OmciGetResponse"
+    message_id = 0x29
+    fields_desc = [
+        ShortField("entity_class", None),
+        ShortField("entity_id", 0),
+        ByteField("success_code", 0),
+        ShortField("attributes_mask", None),
+        ConditionalField(
+            OmciMaskedData("data"), lambda pkt: pkt.success_code == 0)
+    ]
+
+
+class OmciGetAllAlarms(OmciMessage):
+    name = "OmciGetAllAlarms"
+    message_id = 0x4b
+    fields_desc = [
+        ShortField("entity_class", 2),  # Always 2 (ONT data)
+        ShortField("entity_id", 0),  # Always 0 (ONT instance)
+        ByteField("alarm_retrieval_mode", 0)  # 0 or 1
+    ]
+
+
+class OmciGetAllAlarmsResponse(OmciMessage):
+    name = "OmciGetAllAlarmsResponse"
+    message_id = 0x2b
+    fields_desc = [
+        ShortField("entity_class", 2),  # Always 2 (ONT data)
+        ShortField("entity_id", 0),
+        ShortField("number_of_commands", None)
+    ]
+
+
+class OmciGetAllAlarmsNext(OmciMessage):
+    name = "OmciGetAllAlarmsNext"
+    message_id = 0x4c
+    fields_desc = [
+        ShortField("entity_class", 2),  # Always 2 (ONT data)
+        ShortField("entity_id", 0),
+        ShortField("command_sequence_number", None)
+    ]
+
+
+class OmciGetAllAlarmsNextResponse(OmciMessage):
+    name = "OmciGetAllAlarmsNextResponse"
+    message_id = 0x2c
+    fields_desc = [
+        ShortField("entity_class", 2),  # Always 2 (ONT data)
+        ShortField("entity_id", 0),
+        ShortField("alarmed_entity_class", None),
+        ShortField("alarmed_entity_id", 0),
+        StrFixedLenField("alarm_bit_map", None, 27)  # TODO better type?
+    ]
+
+
+class OmciMibUpload(OmciMessage):
+    name = "OmciMibUpload"
+    message_id = 0x4d
+    fields_desc = [
+        ShortField("entity_class", 2),  # Always 2 (ONT data)
+        ShortField("entity_id", 0),
+    ]
+
+
+class OmciMibUploadResponse(OmciMessage):
+    name = "OmciMibUploadResponse"
+    message_id = 0x2d
+    fields_desc = [
+        ShortField("entity_class", 2),  # Always 2 (ONT data)
+        ShortField("entity_id", 0),
+        ShortField("number_of_commands", None)
+    ]
+
+
+class OmciMibUploadNext(OmciMessage):
+    name = "OmciMibUploadNext"
+    message_id = 0x4e
+    fields_desc = [
+        ShortField("entity_class", 2),  # Always 2 (ONT data)
+        ShortField("entity_id", 0),
+        ShortField("command_sequence_number", None)
+    ]
+
+
+class OmciMibUploadNextResponse(OmciMessage):
+    name = "OmciMibUploadNextResponse"
+    message_id = 0x2e
+    fields_desc = [
+        ShortField("entity_class", 2),  # Always 2 (ONT data)
+        ShortField("entity_id", 0),
+        ShortField("object_entity_class", None),
+        ShortField("object_entity_id", 0),
+        ShortField("object_attributes_mask", None),
+        OmciMaskedData("object_data", entity_class='object_entity_class',
+                       attributes_mask='object_attributes_mask')
+    ]
+
+
+class OmciMibReset(OmciMessage):
+    name = "OmciMibReset"
+    message_id = 0x4f
+    fields_desc = [
+        ShortField("entity_class", None),
+        ShortField("entity_id", 0)
+    ]
+
+
+class OmciMibResetResponse(OmciMessage):
+    name = "OmciMibResetResponse"
+    message_id = 0x2f
+    fields_desc = [
+        ShortField("entity_class", None),
+        ShortField("entity_id", 0),
+        ByteField("success_code", 0)
+    ]