diff --git a/python/core/config/__init__.py b/python/core/config/__init__.py
new file mode 100644
index 0000000..b0fb0b2
--- /dev/null
+++ b/python/core/config/__init__.py
@@ -0,0 +1,13 @@
+# 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.
diff --git a/python/core/config/config_backend.py b/python/core/config/config_backend.py
new file mode 100644
index 0000000..d906348
--- /dev/null
+++ b/python/core/config/config_backend.py
@@ -0,0 +1,289 @@
+# 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.
+#
+from consul import Consul, ConsulException
+from common.utils.asleep import asleep
+from requests import ConnectionError
+from twisted.internet.defer import inlineCallbacks, returnValue
+
+import etcd3
+import structlog
+
+
+class ConsulStore(object):
+    """ Config kv store for consul with a cache for quicker subsequent reads
+
+        TODO: This will block the reactor. Should either change
+        whole call stack to yield or put the put/delete transactions into a
+        queue to write later with twisted. Will need a transaction
+        log to ensure we don't lose anything.
+        Making the whole callstack yield is troublesome because other tasks can
+        come in on the side and start modifying things which could be bad.
+    """
+
+    CONNECT_RETRY_INTERVAL_SEC = 1
+    RETRY_BACKOFF = [0.05, 0.1, 0.2, 0.5, 1, 2, 5]
+
+    def __init__(self, host, port, path_prefix):
+
+        self.log = structlog.get_logger()
+        self._consul = Consul(host=host, port=port)
+        self.host = host
+        self.port = port
+        self._path_prefix = path_prefix
+        self._cache = {}
+        self.retries = 0
+
+    def make_path(self, key):
+        return '{}/{}'.format(self._path_prefix, key)
+
+    def __getitem__(self, key):
+        if key in self._cache:
+            return self._cache[key]
+        value = self._kv_get(self.make_path(key))
+        if value is not None:
+            # consul turns empty strings to None, so we do the reverse here
+            self._cache[key] = value['Value'] or ''
+            return value['Value'] or ''
+        else:
+            raise KeyError(key)
+
+    def __contains__(self, key):
+        if key in self._cache:
+            return True
+        value = self._kv_get(self.make_path(key))
+        if value is not None:
+            self._cache[key] = value['Value']
+            return True
+        else:
+            return False
+
+    def __setitem__(self, key, value):
+        try:
+            assert isinstance(value, basestring)
+            self._cache[key] = value
+            self._kv_put(self.make_path(key), value)
+        except Exception, e:
+            self.log.exception('cannot-set-item', e=e)
+
+    def __delitem__(self, key):
+        self._cache.pop(key, None)
+        self._kv_delete(self.make_path(key))
+
+    @inlineCallbacks
+    def _backoff(self, msg):
+        wait_time = self.RETRY_BACKOFF[min(self.retries,
+                                           len(self.RETRY_BACKOFF) - 1)]
+        self.retries += 1
+        self.log.error(msg, retry_in=wait_time)
+        yield asleep(wait_time)
+
+    def _redo_consul_connection(self):
+        self._consul = Consul(host=self.host, port=self.port)
+        self._cache.clear()
+
+    def _clear_backoff(self):
+        if self.retries:
+            self.log.info('reconnected-to-consul', after_retries=self.retries)
+            self.retries = 0
+
+    def _get_consul(self):
+        return self._consul
+
+    # Proxy methods for consul with retry support
+    def _kv_get(self, *args, **kw):
+        return self._retry('GET', *args, **kw)
+
+    def _kv_put(self, *args, **kw):
+        return self._retry('PUT', *args, **kw)
+
+    def _kv_delete(self, *args, **kw):
+        return self._retry('DELETE', *args, **kw)
+
+    def _retry(self, operation, *args, **kw):
+        while 1:
+            try:
+                consul = self._get_consul()
+                self.log.debug('consul', consul=consul, operation=operation,
+                         args=args)
+                if operation == 'GET':
+                    index, result = consul.kv.get(*args, **kw)
+                elif operation == 'PUT':
+                     result = consul.kv.put(*args, **kw)
+                elif operation == 'DELETE':
+                    result = consul.kv.delete(*args, **kw)
+                else:
+                    # Default case - consider operation as a function call
+                    result = operation(*args, **kw)
+                self._clear_backoff()
+                break
+            except ConsulException, e:
+                self.log.exception('consul-not-up', e=e)
+                self._backoff('consul-not-up')
+            except ConnectionError, e:
+                self.log.exception('cannot-connect-to-consul', e=e)
+                self._backoff('cannot-connect-to-consul')
+            except Exception, e:
+                self.log.exception(e)
+                self._backoff('unknown-error')
+            self._redo_consul_connection()
+
+        return result
+
+
+class EtcdStore(object):
+    """ Config kv store for etcd with a cache for quicker subsequent reads
+
+        TODO: This will block the reactor. Should either change
+        whole call stack to yield or put the put/delete transactions into a
+        queue to write later with twisted. Will need a transaction
+        log to ensure we don't lose anything.
+        Making the whole callstack yield is troublesome because other tasks can
+        come in on the side and start modifying things which could be bad.
+    """
+
+    CONNECT_RETRY_INTERVAL_SEC = 1
+    RETRY_BACKOFF = [0.05, 0.1, 0.2, 0.5, 1, 2, 5]
+
+    def __init__(self, host, port, path_prefix):
+
+        self.log = structlog.get_logger()
+        self._etcd = etcd3.client(host=host, port=port)
+        self.host = host
+        self.port = port
+        self._path_prefix = path_prefix
+        self._cache = {}
+        self.retries = 0
+
+    def make_path(self, key):
+        return '{}/{}'.format(self._path_prefix, key)
+
+    def __getitem__(self, key):
+        if key in self._cache:
+            return self._cache[key]
+        (value, meta) = self._kv_get(self.make_path(key))
+        if value is not None:
+            self._cache[key] = value
+            return value
+        else:
+            raise KeyError(key)
+
+    def __contains__(self, key):
+        if key in self._cache:
+            return True
+        (value, meta) = self._kv_get(self.make_path(key))
+        if value is not None:
+            self._cache[key] = value
+            return True
+        else:
+            return False
+
+    def __setitem__(self, key, value):
+        try:
+            assert isinstance(value, basestring)
+            self._cache[key] = value
+            self._kv_put(self.make_path(key), value)
+        except Exception, e:
+            self.log.exception('cannot-set-item', e=e)
+
+    def __delitem__(self, key):
+        self._cache.pop(key, None)
+        self._kv_delete(self.make_path(key))
+
+    @inlineCallbacks
+    def _backoff(self, msg):
+        wait_time = self.RETRY_BACKOFF[min(self.retries,
+                                           len(self.RETRY_BACKOFF) - 1)]
+        self.retries += 1
+        self.log.error(msg, retry_in=wait_time)
+        yield asleep(wait_time)
+
+    def _redo_etcd_connection(self):
+        self._etcd = etcd3.client(host=self.host, port=self.port)
+        self._cache.clear()
+
+    def _clear_backoff(self):
+        if self.retries:
+            self.log.info('reconnected-to-etcd', after_retries=self.retries)
+            self.retries = 0
+
+    def _get_etcd(self):
+        return self._etcd
+
+    # Proxy methods for etcd with retry support
+    def _kv_get(self, *args, **kw):
+        return self._retry('GET', *args, **kw)
+
+    def _kv_put(self, *args, **kw):
+        return self._retry('PUT', *args, **kw)
+
+    def _kv_delete(self, *args, **kw):
+        return self._retry('DELETE', *args, **kw)
+
+    def _retry(self, operation, *args, **kw):
+
+        # etcd data sometimes contains non-utf8 sequences, replace
+        self.log.debug('backend-op',
+                  operation=operation,
+                  args=map(lambda x : unicode(x,'utf8','replace'), args),
+                  kw=kw)
+
+        while 1:
+            try:
+                etcd = self._get_etcd()
+                self.log.debug('etcd', etcd=etcd, operation=operation,
+                    args=map(lambda x : unicode(x,'utf8','replace'), args))
+                if operation == 'GET':
+                    (value, meta) = etcd.get(*args, **kw)
+                    result = (value, meta)
+                elif operation == 'PUT':
+                    result = etcd.put(*args, **kw)
+                elif operation == 'DELETE':
+                    result = etcd.delete(*args, **kw)
+                else:
+                    # Default case - consider operation as a function call
+                    result = operation(*args, **kw)
+                self._clear_backoff()
+                break
+            except Exception, e:
+                self.log.exception(e)
+                self._backoff('unknown-error-with-etcd')
+            self._redo_etcd_connection()
+
+        return result
+
+
+def load_backend(store_id, store_prefix, args):
+    """ Return the kv store backend based on the command line arguments
+    """
+
+    def load_consul_store():
+        instance_core_store_prefix = '{}/{}'.format(store_prefix, store_id)
+
+        host, port = args.consul.split(':', 1)
+        return ConsulStore(host, int(port), instance_core_store_prefix)
+
+    def load_etcd_store():
+        instance_core_store_prefix = '{}/{}'.format(store_prefix, store_id)
+
+        host, port = args.etcd.split(':', 1)
+        return EtcdStore(host, int(port), instance_core_store_prefix)
+
+    loaders = {
+        'none': lambda: None,
+        'consul': load_consul_store,
+        'etcd': load_etcd_store
+    }
+
+    return loaders[args.backend]()
diff --git a/python/core/config/config_branch.py b/python/core/config/config_branch.py
new file mode 100644
index 0000000..207818b
--- /dev/null
+++ b/python/core/config/config_branch.py
@@ -0,0 +1,53 @@
+#
+# 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.
+#
+
+"""
+Class to hold revisions, latest revision, etc., for a config node, used
+for the active committed revisions or revisions part of a transaction.
+"""
+
+from collections import OrderedDict
+from weakref import WeakValueDictionary
+
+
+class ConfigBranch(object):
+
+    __slots__ = (
+        '_node',  # ref to node
+        '_txid',  # txid for this branch (None for the committed branch)
+        '_origin',  # _latest at time of branching on default branch
+        '_revs',  # dict of rev-hash to ref of ConfigRevision
+        '_latest',  # ref to latest committed ConfigRevision
+        '__weakref__'
+    )
+
+    def __init__(self, node, txid=None, origin=None, auto_prune=True):
+        self._node = node
+        self._txid = txid
+        self._origin = origin
+        self._revs = WeakValueDictionary() if auto_prune else OrderedDict()
+        self._latest = origin
+
+    def __getitem__(self, hash):
+        return self._revs[hash]
+
+    @property
+    def latest(self):
+        return self._latest
+
+    @property
+    def origin(self):
+        return self._origin
diff --git a/python/core/config/config_event_bus.py b/python/core/config/config_event_bus.py
new file mode 100644
index 0000000..e56d77a
--- /dev/null
+++ b/python/core/config/config_event_bus.py
@@ -0,0 +1,66 @@
+# 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.
+import structlog
+from enum import Enum
+from google.protobuf.json_format import MessageToDict
+from google.protobuf.message import Message
+from simplejson import dumps
+
+from common.event_bus import EventBusClient
+from voltha.core.config.config_proxy import CallbackType
+from voltha.protos import third_party
+from voltha.protos.events_pb2 import ConfigEvent, ConfigEventType
+
+IGNORED_CALLBACKS = [CallbackType.PRE_ADD, CallbackType.GET,
+                     CallbackType.POST_LISTCHANGE, CallbackType.PRE_REMOVE,
+                     CallbackType.PRE_UPDATE]
+
+log = structlog.get_logger()
+
+class ConfigEventBus(object):
+
+    __slots__ = (
+        '_event_bus_client',  # The event bus client used to publish events.
+        '_topic'  # the topic to publish to
+    )
+
+    def __init__(self):
+        self._event_bus_client = EventBusClient()
+        self._topic = 'model-change-events'
+
+    def advertise(self, type, data, hash=None):
+        if type in IGNORED_CALLBACKS:
+            log.info('Ignoring event {} with data {}'.format(type, data))
+            return
+
+        if type is CallbackType.POST_ADD:
+            kind = ConfigEventType.add
+        elif type is CallbackType.POST_REMOVE:
+            kind = ConfigEventType.remove
+        else:
+            kind = ConfigEventType.update
+
+        if isinstance(data, Message):
+            msg = dumps(MessageToDict(data, True, True))
+        else:
+            msg = data
+
+        event = ConfigEvent(
+            type=kind,
+            hash=hash,
+            data=msg
+        )
+
+        self._event_bus_client.publish(self._topic, event)
+
diff --git a/python/core/config/config_node.py b/python/core/config/config_node.py
new file mode 100644
index 0000000..ab73484
--- /dev/null
+++ b/python/core/config/config_node.py
@@ -0,0 +1,617 @@
+#
+# 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.
+#
+from copy import copy
+
+from jsonpatch import JsonPatch
+from jsonpatch import make_patch
+
+from common.utils.json_format import MessageToDict
+from voltha.core.config.config_branch import ConfigBranch
+from voltha.core.config.config_event_bus import ConfigEventBus
+from voltha.core.config.config_proxy import CallbackType, ConfigProxy
+from voltha.core.config.config_rev import is_proto_message, children_fields, \
+    ConfigRevision, access_rights
+from voltha.core.config.config_rev_persisted import PersistedConfigRevision
+from voltha.core.config.merge_3way import merge_3way
+from voltha.protos import third_party
+from voltha.protos import meta_pb2
+
+import structlog
+
+log = structlog.get_logger()
+
+def message_to_dict(m):
+    return MessageToDict(m, True, True, False)
+
+
+def check_access_violation(new_msg, old_msg):
+    """Raise ValueError if attempt is made to change a read-only field"""
+    access_map = access_rights(new_msg.__class__)
+    violated_fields = []
+    for field_name, access in access_map.iteritems():
+        if access == meta_pb2.READ_ONLY:
+            if getattr(new_msg, field_name) != getattr(old_msg, field_name):
+                violated_fields.append(field_name)
+    if violated_fields:
+        raise ValueError('Cannot change read-only field(s) %s' %
+                         ', '.join('"%s"' % f for f in violated_fields))
+
+
+def find_rev_by_key(revs, keyname, value):
+    for i, rev in enumerate(revs):
+        if getattr(rev._config._data, keyname) == value:
+            return i, rev
+    raise KeyError('key {}={} not found'.format(keyname, value))
+
+
+class ConfigNode(object):
+    """
+    Represents a configuration node which can hold a number of revisions
+    of the configuration for this node.
+    When the configuration changes, the new version is appended to the
+    node.
+    Initial data must be a protobuf message and it will determine the type of
+    this node.
+    """
+    __slots__ = (
+        '_root',  # ref to root node
+        '_type',  # node type, as __class__ of protobuf message
+        '_branches',  # dict of transaction branches and a default (committed)
+                      # branch
+        '_tags',  # dict of tag-name to ref of ConfigRevision
+        '_proxy',  # ref to proxy observer or None if no proxy assigned
+        '_event_bus',  # ref to event_bus or None if no event bus is assigned
+        '_auto_prune'
+    )
+
+    def __init__(self, root, initial_data, auto_prune=True, txid=None):
+        self._root = root
+        self._branches = {}
+        self._tags = {}
+        self._proxy = None
+        self._event_bus = None
+        self._auto_prune = auto_prune
+
+        if isinstance(initial_data, type):
+            self._type = initial_data
+        elif is_proto_message(initial_data):
+            self._type = initial_data.__class__
+            copied_data = initial_data.__class__()
+            copied_data.CopyFrom(initial_data)
+            self._initialize(copied_data, txid)
+        else:
+            raise NotImplementedError()
+
+    def _mknode(self, *args, **kw):
+        return ConfigNode(self._root, *args, **kw)
+
+    def _mkrev(self, *args, **kw):
+        return self._root.mkrev(*args, **kw)
+
+    def _initialize(self, data, txid):
+        # separate external children data away from locally stored data
+        # based on child_node annotations in protobuf
+        children = {}
+        for field_name, field in children_fields(self._type).iteritems():
+            field_value = getattr(data, field_name)
+            if field.is_container:
+                if field.key:
+                    keys_seen = set()
+                    children[field_name] = lst = []
+                    for v in field_value:
+                        rev = self._mknode(v, txid=txid).latest
+                        key = getattr(v, field.key)
+                        if key in keys_seen:
+                            raise ValueError('Duplicate key "{}"'.format(key))
+                        lst.append(rev)
+                        keys_seen.add(key)
+                else:
+                    children[field_name] = [
+                        self._mknode(v, txid=txid).latest for v in field_value]
+            else:
+                children[field_name] = [
+                    self._mknode(field_value, txid=txid).latest]
+            data.ClearField(field_name)
+
+        branch = ConfigBranch(self, auto_prune=self._auto_prune)
+        rev = self._mkrev(branch, data, children)
+        self._make_latest(branch, rev)
+        self._branches[txid] = branch
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ accessors ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    # these convenience short-cuts only work for the committed branch
+
+    @property
+    def revisions(self):
+        return [r._hash for r in self._branches[None]._revs.itervalues()]
+
+    @property
+    def latest(self):
+        return self._branches[None]._latest
+
+    def __getitem__(self, hash):
+        return self._branches[None]._revs[hash]
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ get operation ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def get(self, path=None, hash=None, depth=0, deep=False, txid=None):
+
+        # depth preparation
+        if deep:
+            depth = -1
+
+        # path preparation
+        path = '' if path is None else path
+        while path.startswith('/'):
+            path = path[1:]
+
+        # determine branch; if lookup fails, it is ok to use default branch
+        branch = self._branches.get(txid, None) or self._branches[None]
+
+        # determine rev
+        if hash is not None:
+            rev = branch._revs[hash]
+        else:
+            rev = branch.latest
+
+        return self._get(rev, path, depth)
+
+    def _get(self, rev, path, depth):
+
+        if not path:
+            return self._do_get(rev, depth)
+
+        # ... otherwise
+        name, _, path = path.partition('/')
+        field = children_fields(self._type)[name]
+        if field.is_container:
+            if field.key:
+                children = rev._children[name]
+                if path:
+                    # need to escalate further
+                    key, _, path = path.partition('/')
+                    key = field.key_from_str(key)
+                    _, child_rev = find_rev_by_key(children, field.key, key)
+                    child_node = child_rev.node
+                    return child_node._get(child_rev, path, depth)
+                else:
+                    # we are the node of interest
+                    response = []
+                    for child_rev in children:
+                        child_node = child_rev.node
+                        value = child_node._do_get(child_rev, depth)
+                        response.append(value)
+                    return response
+            else:
+                if path:
+                    raise LookupError(
+                        'Cannot index into container with no key defined')
+                response = []
+                for child_rev in rev._children[name]:
+                    child_node = child_rev.node
+                    value = child_node._do_get(child_rev, depth)
+                    response.append(value)
+                return response
+        else:
+            child_rev = rev._children[name][0]
+            child_node = child_rev.node
+            return child_node._get(child_rev, path, depth)
+
+    def _do_get(self, rev, depth):
+        msg = rev.get(depth)
+        if self._proxy is not None:
+            msg = self._proxy.invoke_callbacks(CallbackType.GET, msg)
+        return msg
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~ update operation ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def update(self, path, data, strict=False, txid=None, mk_branch=None):
+
+        while path.startswith('/'):
+            path = path[1:]
+
+        try:
+            branch = self._branches[txid]
+        except KeyError:
+            branch = mk_branch(self)
+
+        if not path:
+            return self._do_update(branch, data, strict)
+
+        rev = branch._latest  # change is always made to the latest
+        name, _, path = path.partition('/')
+        field = children_fields(self._type)[name]
+        if field.is_container:
+            if not path:
+                raise ValueError('Cannot update a list')
+            if field.key:
+                key, _, path = path.partition('/')
+                key = field.key_from_str(key)
+                children = copy(rev._children[name])
+                idx, child_rev = find_rev_by_key(children, field.key, key)
+                child_node = child_rev.node
+                # chek if deep copy will work better
+                new_child_rev = child_node.update(
+                    path, data, strict, txid, mk_branch)
+                if new_child_rev.hash == child_rev.hash:
+                    # When the new_child_rev goes out of scope,
+                    # it's destructor gets invoked as it is not being
+                    # referred by any other data structures.  To prevent
+                    # this to trigger the hash it is holding from being
+                    # erased in the db, its hash is set to None.  If the
+                    # new_child_rev object is pointing at the same address
+                    # as the child_rev address then do not clear the hash
+                    if new_child_rev != child_rev:
+                        log.debug('clear-hash',
+                             hash=new_child_rev.hash, object_ref=new_child_rev)
+                        new_child_rev.clear_hash()
+                    return branch._latest
+                if getattr(new_child_rev.data, field.key) != key:
+                    raise ValueError('Cannot change key field')
+                children[idx] = new_child_rev
+                rev = rev.update_children(name, children, branch)
+                self._make_latest(branch, rev)
+                return rev
+            else:
+                raise ValueError('Cannot index into container with no keys')
+
+        else:
+            child_rev = rev._children[name][0]
+            child_node = child_rev.node
+            new_child_rev = child_node.update(
+                path, data, strict, txid, mk_branch)
+            rev = rev.update_children(name, [new_child_rev], branch)
+            self._make_latest(branch, rev)
+            return rev
+
+    def _do_update(self, branch, data, strict):
+        if not isinstance(data, self._type):
+            raise ValueError(
+                '"{}" is not a valid data type for this node'.format(
+                    data.__class__.__name__))
+        self._test_no_children(data)
+        if self._proxy is not None:
+            self._proxy.invoke_callbacks(CallbackType.PRE_UPDATE, data)
+
+        if branch._latest.data != data:
+            if strict:
+                # check if attempt is made to change read-only field
+                check_access_violation(data, branch._latest.data)
+            rev = branch._latest.update_data(data, branch)
+            self._make_latest(branch, rev,
+                              ((CallbackType.POST_UPDATE, rev.data),))
+            return rev
+        else:
+            return branch._latest
+
+    def _make_latest(self, branch, rev, change_announcements=()):
+        # Update the latest branch only when the hash between the previous
+        # data and the new rev is different, otherwise this will trigger the
+        # data already saved in the db (with that hash) to be erased
+        if rev.hash not in branch._revs:
+            branch._revs[rev.hash] = rev
+
+        if not branch._latest or rev.hash != branch._latest.hash:
+            branch._latest = rev
+
+        # announce only if this is main branch
+        if change_announcements and branch._txid is None:
+
+            if self._proxy is not None:
+                for change_type, data in change_announcements:
+                    # since the callback may operate on the config tree,
+                    # we have to defer the execution of the callbacks till
+                    # the change is propagated to the root, then root will
+                    # call the callbacks
+                    self._root.enqueue_callback(
+                        self._proxy.invoke_callbacks,
+                        change_type,
+                        data,
+                        proceed_on_errors=1,
+                    )
+
+            for change_type, data in change_announcements:
+                self._root.enqueue_notification_callback(
+                    self._mk_event_bus().advertise,
+                    change_type,
+                    data,
+                    hash=rev.hash
+                )
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ add operation ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def add(self, path, data, txid=None, mk_branch=None):
+        while path.startswith('/'):
+            path = path[1:]
+        if not path:
+            raise ValueError('Cannot add to non-container node')
+
+        try:
+            branch = self._branches[txid]
+        except KeyError:
+            branch = mk_branch(self)
+
+        rev = branch._latest  # change is always made to latest
+        name, _, path = path.partition('/')
+        field = children_fields(self._type)[name]
+        if field.is_container:
+            if not path:
+                # we do need to add a new child to the field
+                if field.key:
+                    if self._proxy is not None:
+                        self._proxy.invoke_callbacks(
+                            CallbackType.PRE_ADD, data)
+                    children = copy(rev._children[name])
+                    key = getattr(data, field.key)
+                    try:
+                        find_rev_by_key(children, field.key, key)
+                    except KeyError:
+                        pass
+                    else:
+                        raise ValueError('Duplicate key "{}"'.format(key))
+                    child_rev = self._mknode(data).latest
+                    children.append(child_rev)
+                    rev = rev.update_children(name, children, branch)
+                    self._make_latest(branch, rev,
+                                      ((CallbackType.POST_ADD, data),))
+                    return rev
+                else:
+                    # adding to non-keyed containers not implemented yet
+                    raise ValueError('Cannot add to non-keyed container')
+            else:
+                if field.key:
+                    # need to escalate
+                    key, _, path = path.partition('/')
+                    key = field.key_from_str(key)
+                    children = copy(rev._children[name])
+                    idx, child_rev = find_rev_by_key(children, field.key, key)
+                    child_node = child_rev.node
+                    new_child_rev = child_node.add(path, data, txid, mk_branch)
+                    children[idx] = new_child_rev
+                    rev = rev.update_children(name, children, branch)
+                    self._make_latest(branch, rev)
+                    return rev
+                else:
+                    raise ValueError(
+                        'Cannot index into container with no keys')
+        else:
+            raise ValueError('Cannot add to non-container field')
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~ remove operation ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def remove(self, path, txid=None, mk_branch=None):
+        while path.startswith('/'):
+            path = path[1:]
+        if not path:
+            raise ValueError('Cannot remove from non-container node')
+
+        try:
+            branch = self._branches[txid]
+        except KeyError:
+            branch = mk_branch(self)
+
+        rev = branch._latest  # change is always made to latest
+        name, _, path = path.partition('/')
+        field = children_fields(self._type)[name]
+        if field.is_container:
+            if not path:
+                raise ValueError("Cannot remove without a key")
+            if field.key:
+                key, _, path = path.partition('/')
+                key = field.key_from_str(key)
+                if path:
+                    # need to escalate
+                    children = copy(rev._children[name])
+                    idx, child_rev = find_rev_by_key(children, field.key, key)
+                    child_node = child_rev.node
+                    new_child_rev = child_node.remove(path, txid, mk_branch)
+                    children[idx] = new_child_rev
+                    rev = rev.update_children(name, children, branch)
+                    self._make_latest(branch, rev)
+                    return rev
+                else:
+                    # need to remove from this very node
+                    children = copy(rev._children[name])
+                    idx, child_rev = find_rev_by_key(children, field.key, key)
+                    if self._proxy is not None:
+                        data = child_rev.data
+                        self._proxy.invoke_callbacks(
+                            CallbackType.PRE_REMOVE, data)
+                        post_anno = ((CallbackType.POST_REMOVE, data),)
+                    else:
+                        post_anno = ((CallbackType.POST_REMOVE, child_rev.data),)
+                    del children[idx]
+                    rev = rev.update_children(name, children, branch)
+                    self._make_latest(branch, rev, post_anno)
+                    return rev
+            else:
+                raise ValueError('Cannot remove from non-keyed container')
+        else:
+            raise ValueError('Cannot remove non-conatiner field')
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Branching ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def _mk_txbranch(self, txid):
+        branch_point = self._branches[None].latest
+        branch = ConfigBranch(self, txid, branch_point)
+        self._branches[txid] = branch
+        return branch
+
+    def _del_txbranch(self, txid):
+        del self._branches[txid]
+
+    def _merge_txbranch(self, txid, dry_run=False):
+        """
+        Make latest in branch to be latest in the common branch, but only
+        if no conflict is detected. Conflict is where the txbranch branch
+        point no longer matches the latest in the default branch. This has
+        to be verified recursively.
+        """
+
+        def merge_child(child_rev):
+            child_branch = child_rev._branch
+            if child_branch._txid == txid:
+                child_rev = child_branch._node._merge_txbranch(txid, dry_run)
+            return child_rev
+
+        src_branch = self._branches[txid]
+        dst_branch = self._branches[None]
+
+        fork_rev = src_branch.origin  # rev from which src branch was made
+        src_rev = src_branch.latest  # head rev of source branch
+        dst_rev = dst_branch.latest  # head rev of target branch
+
+        rev, changes = merge_3way(
+            fork_rev, src_rev, dst_rev, merge_child, dry_run)
+
+        if not dry_run:
+            self._make_latest(dst_branch, rev, change_announcements=changes)
+            del self._branches[txid]
+
+        return rev
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Diff utility ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def diff(self, hash1, hash2=None, txid=None):
+        branch = self._branches[txid]
+        rev1 = branch[hash1]
+        rev2 = branch[hash2] if hash2 else branch._latest
+        if rev1.hash == rev2.hash:
+            return JsonPatch([])
+        else:
+            dict1 = message_to_dict(rev1.data)
+            dict2 = message_to_dict(rev2.data)
+            return make_patch(dict1, dict2)
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Tagging utility ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def tag(self, tag, hash=None):
+        branch = self._branches[None]  # tag only what has been committed
+        rev = branch._latest if hash is None else branch._revs[hash]
+        self._tags[tag] = rev
+        self.persist_tags()
+        return self
+
+    @property
+    def tags(self):
+        return sorted(self._tags.iterkeys())
+
+    def by_tag(self, tag):
+        """
+        Return revision based on tag
+        :param tag: previously registered tag value
+        :return: revision object
+        """
+        return self._tags[tag]
+
+    def diff_by_tag(self, tag1, tag2):
+        return self.diff(self._tags[tag1].hash, self._tags[tag2].hash)
+
+    def delete_tag(self, tag):
+        del self._tags[tag]
+        self.persist_tags()
+
+    def delete_tags(self, *tags):
+        for tag in tags:
+            del self._tags[tag]
+        self.persist_tags()
+
+    def prune_untagged(self):
+        branch = self._branches[None]
+        keep = set(rev.hash for rev in self._tags.itervalues())
+        keep.add(branch._latest.hash)
+        for hash in branch._revs.keys():
+            if hash not in keep:
+                del branch._revs[hash]
+        return self
+
+    def persist_tags(self):
+        """
+        Persist tag information to the backend
+        """
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Internals ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def _test_no_children(self, data):
+        for field_name, field in children_fields(self._type).items():
+            field_value = getattr(data, field_name)
+            if field.is_container:
+                if len(field_value):
+                    raise NotImplementedError(
+                        'Cannot update external children')
+            else:
+                if data.HasField(field_name):
+                    raise NotImplementedError(
+                        'Cannot update externel children')
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Node proxy ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def get_proxy(self, path, exclusive=False):
+        return self._get_proxy(path, self, path, exclusive)
+
+    def _get_proxy(self, path, root, full_path, exclusive):
+        while path.startswith('/'):
+            path = path[1:]
+        if not path:
+            return self._mk_proxy(root, full_path, exclusive)
+
+        # need to escalate
+        rev = self._branches[None]._latest
+        name, _, path = path.partition('/')
+        field = children_fields(self._type)[name]
+        if field.is_container:
+            if not path:
+                raise ValueError('Cannot proxy a container field')
+            if field.key:
+                key, _, path = path.partition('/')
+                key = field.key_from_str(key)
+                children = rev._children[name]
+                _, child_rev = find_rev_by_key(children, field.key, key)
+                child_node = child_rev.node
+                return child_node._get_proxy(path, root, full_path, exclusive)
+
+            raise ValueError('Cannot index into container with no keys')
+
+        else:
+            child_rev = rev._children[name][0]
+            child_node = child_rev.node
+            return child_node._get_proxy(path, root, full_path, exclusive)
+
+    def _mk_proxy(self, root, full_path, exclusive):
+        if self._proxy is None:
+            self._proxy = ConfigProxy(root, self, full_path, exclusive)
+        else:
+            if self._proxy.exclusive:
+                raise ValueError('Node is already owned exclusively')
+        return self._proxy
+
+    def _mk_event_bus(self):
+        if self._event_bus is None:
+            self._event_bus = ConfigEventBus()
+        return self._event_bus
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~ Persistence loading ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def load_latest(self, latest_hash):
+
+        root = self._root
+        kv_store = root._kv_store
+
+        branch = ConfigBranch(node=self, auto_prune=self._auto_prune)
+        rev = PersistedConfigRevision.load(
+            branch, kv_store, self._type, latest_hash)
+        self._make_latest(branch, rev)
+        self._branches[None] = branch
diff --git a/python/core/config/config_proxy.py b/python/core/config/config_proxy.py
new file mode 100644
index 0000000..57d8150
--- /dev/null
+++ b/python/core/config/config_proxy.py
@@ -0,0 +1,155 @@
+#
+# 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 voltha.core.config.config_txn import ConfigTransaction
+
+log = structlog.get_logger()
+
+
+class OperationContext(object):
+    def __init__(self, path=None, data=None, field_name=None, child_key=None):
+        self.path = path
+        self._data = data
+        self.field_name = field_name
+        self.child_key = child_key
+    @property
+    def data(self):
+        return self._data
+    def update(self, data):
+        self._data = data
+        return self
+    def __repr__(self):
+        return 'OperationContext({})'.format(self.__dict__)
+
+
+class CallbackType(Enum):
+
+    # GET hooks are called after the data is retrieved and can be used to
+    # augment the data (they should only augment fields marked as REAL_TIME
+    GET = 1
+
+    # PRE_UPDATE hooks are called before the change is made and are supposed
+    # to be used to reject the data by raising an exception. If they don't,
+    # the change will be applied.
+    PRE_UPDATE = 2
+
+    # POST_UPDATE hooks are called after the update has occurred and can
+    # be used to deal with the change. For instance, an adapter can use the
+    # callback to trigger the south-bound configuration
+    POST_UPDATE = 3
+
+    # These behave similarly to the update callbacks as described above.
+    PRE_ADD = 4
+    POST_ADD = 5
+    PRE_REMOVE = 6
+    POST_REMOVE = 7
+
+    # Bulk list change due to transaction commit that changed items in
+    # non-keyed container fields
+    POST_LISTCHANGE = 8
+
+
+class ConfigProxy(object):
+    """
+    Allows an entity to look at a sub-tree and see it as it was the whole tree
+    """
+    __slots__ = (
+        '_root',
+        '_node',
+        '_path',
+        '_exclusive',
+        '_callbacks'
+    )
+
+    def __init__(self, root, node, path, exclusive):
+        self._root = root
+        self._node = node
+        self._exclusive = exclusive
+        self._path = path  # full path to proxied node
+        self._callbacks = {}  # call back type -> list of callbacks
+
+    @property
+    def exclusive(self):
+        return self._exclusive
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~ CRUD handlers ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def get(self, path='/', depth=None, deep=None, txid=None):
+        return self._node.get(path, depth=depth, deep=deep, txid=txid)
+
+    def update(self, path, data, strict=False, txid=None):
+        assert path.startswith('/')
+        full_path = self._path if path == '/' else self._path + path
+        return self._root.update(full_path, data, strict, txid=txid)
+
+    def add(self, path, data, txid=None):
+        assert path.startswith('/')
+        full_path = self._path if path == '/' else self._path + path
+        return self._root.add(full_path, data, txid=txid)
+
+    def remove(self, path, txid=None):
+        assert path.startswith('/')
+        full_path = self._path if path == '/' else self._path + path
+        return self._root.remove(full_path, txid=txid)
+
+    # ~~~~~~~~~~~~~~~~~~~~~~~~~~ Transaction support ~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def open_transaction(self):
+        """Open a new transaction"""
+        txid = self._root.mk_txbranch()
+        return ConfigTransaction(self, txid)
+
+    def commit_transaction(self, txid):
+        """
+        If having an open transaction, commit it now. Will raise exception
+        if conflict is detected. Either way, transaction will be deleted.
+        """
+        self._root.fold_txbranch(txid)
+
+    def cancel_transaction(self, txid):
+        """
+        Cancel current transaction if we are in a transaction. Always succeeds.
+        """
+        self._root.del_txbranch(txid)
+
+    # ~~~~~~~~~~~~~~~~~~~~~~ Callbacks registrations ~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def register_callback(self, callback_type, callback, *args, **kw):
+        lst = self._callbacks.setdefault(callback_type, [])
+        lst.append((callback, args, kw))
+
+    def unregister_callback(self, callback_type, callback, *args, **kw):
+        lst = self._callbacks.setdefault(callback_type, [])
+        if (callback, args, kw) in lst:
+            lst.remove((callback, args, kw))
+
+    # ~~~~~~~~~~~~~~~~~~~~~ Callback dispatch ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def invoke_callbacks(self, callback_type, context, proceed_on_errors=False):
+        lst = self._callbacks.get(callback_type, [])
+        for callback, args, kw in lst:
+            try:
+                context = callback(context, *args, **kw)
+            except Exception, e:
+                if proceed_on_errors:
+                    log.exception(
+                        'call-back-error', callback_type=callback_type,
+                        context=context, e=e)
+                else:
+                    raise
+        return context
diff --git a/python/core/config/config_rev.py b/python/core/config/config_rev.py
new file mode 100644
index 0000000..8bfac18
--- /dev/null
+++ b/python/core/config/config_rev.py
@@ -0,0 +1,342 @@
+#
+# 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.
+#
+
+"""
+Immutable classes to store config revision information arranged in a tree.
+
+Immutability cannot be enforced in Python, so anyoen working with these
+classes directly must obey the rules.
+"""
+
+import weakref
+from copy import copy
+from hashlib import md5
+
+from google.protobuf.descriptor import Descriptor
+from simplejson import dumps
+
+from common.utils.json_format import MessageToJson
+from voltha.protos import third_party
+from voltha.protos import meta_pb2
+
+import structlog
+
+log = structlog.get_logger()
+
+def is_proto_message(o):
+    """
+    Return True if object o appears to be a protobuf message; False otherwise.
+    """
+    # use a somewhat empirical approach to decide if something looks like
+    # a protobuf message
+    return isinstance(getattr(o, 'DESCRIPTOR', None), Descriptor)
+
+
+def message_to_json_concise(m):
+    """
+    Return the most concise string representation of a protobuf. Good for
+    things where size matters (e.g., generating hash).
+    """
+    return MessageToJson(m, False, True, False)
+
+
+_rev_cache = weakref.WeakValueDictionary()  # cache of config revs
+
+
+_children_fields_cache = {}  # to memoize externally stored field name info
+
+
+class _ChildType(object):
+    """Used to store key metadata about child_node fields in protobuf messages.
+    """
+    __slots__ = (
+        '_module',
+        '_type',
+        '_is_container',
+        '_key',
+        '_key_from_str'
+    )
+
+    def __init__(self, module, type, is_container,
+                 key=None, key_from_str=None):
+        self._module = module
+        self._type = type
+        self._is_container = is_container
+        self._key = key
+        self._key_from_str = key_from_str
+
+    @property
+    def is_container(self):
+        return self._is_container
+
+    @property
+    def key(self):
+        return self._key
+
+    @property
+    def key_from_str(self):
+        return self._key_from_str
+
+    @property
+    def module(self):
+        return self._module
+
+    @property
+    def type(self):
+        return self._type
+
+
+def children_fields(cls):
+    """
+    Return a map of externally stored fields for this protobuf message type.
+    What is stored as branch node is determined by the "child_node"
+    annotation in the protobuf definitions.
+    With each external field, we store if the field is a container, if a
+    container is keyed (indexed), and what is the function that converts
+    path substring back to the key.
+    """
+    names = _children_fields_cache.get(cls)
+
+    if names is None:
+        names = {}
+
+        for field in cls.DESCRIPTOR.fields:
+
+            if field.has_options:
+                options = field.GetOptions()
+
+                if options.HasExtension(meta_pb2.child_node):
+                    is_container = field.label == 3
+                    meta = options.Extensions[meta_pb2.child_node]
+                    key_from_str = None
+
+                    if meta.key:
+                        key_field = field.message_type.fields_by_name[meta.key]
+                        key_type = key_field.type
+
+                        if key_type == key_field.TYPE_STRING:
+                            key_from_str = lambda s: s
+
+                        elif key_type in (
+                                key_field.TYPE_FIXED32,
+                                key_field.TYPE_FIXED64,
+                                key_field.TYPE_INT32,
+                                key_field.TYPE_INT64,
+                                key_field.TYPE_SFIXED32,
+                                key_field.TYPE_SFIXED64,
+                                key_field.TYPE_SINT32,
+                                key_field.TYPE_SINT64,
+                                key_field.TYPE_UINT32,
+                                key_field.TYPE_UINT64):
+                            key_from_str = lambda s: int(s)
+
+                        else:
+                            raise NotImplementedError()
+
+                    field_class = field.message_type._concrete_class
+                    names[field.name] = _ChildType(
+                        module=field_class.__module__,
+                        type=field_class.__name__,
+                        is_container=is_container,
+                        key=meta.key,
+                        key_from_str=key_from_str
+                    )
+
+        _children_fields_cache[cls] = names
+
+    return names
+
+
+_access_right_cache = {}  # to memoize field access right restrictions
+
+
+def access_rights(cls):
+    """
+    Determine the access rights for each field and cache these maps for
+    fast retrieval.
+    """
+    access_map = _access_right_cache.get(cls)
+    if access_map is None:
+        access_map = {}
+        for field in cls.DESCRIPTOR.fields:
+            if field.has_options:
+                options = field.GetOptions()
+                if options.HasExtension(meta_pb2.access):
+                    access = options.Extensions[meta_pb2.access]
+                    access_map[field.name] = access
+        _access_right_cache[cls] = access_map
+    return access_map
+
+
+class ConfigDataRevision(object):
+    """
+    Holds a specific snapshot of the local configuration for config node.
+    It shall be treated as an immutable object, although in Python this is
+    very difficult to enforce!
+    As such, we can compute a unique hash based on the config data which
+    can be used to establish equivalence. It also has a time-stamp to track
+    changes.
+
+    This object must be treated as immutable, including its nested config data.
+    This is very important. The entire config module depends on hashes
+    we create over the data, so altering the data can lead to unpredictable
+    detriments.
+    """
+
+    __slots__ = (
+        '_data',
+        '_hash',
+        '__weakref__'
+    )
+
+    def __init__(self, data):
+        self._data = data
+        self._hash = self._hash_data(data)
+
+    @property
+    def data(self):
+        return self._data
+
+    @property
+    def hash(self):
+        return self._hash
+
+    @staticmethod
+    def _hash_data(data):
+        """Hash function to be used to track version changes of config nodes"""
+        if isinstance(data, (dict, list)):
+            to_hash = dumps(data, sort_keys=True)
+        elif is_proto_message(data):
+            to_hash = ':'.join((
+                data.__class__.__module__,
+                data.__class__.__name__,
+                data.SerializeToString()))
+        else:
+            to_hash = str(hash(data))
+        return md5(to_hash).hexdigest()[:12]
+
+
+class ConfigRevision(object):
+    """
+    Holds not only the local config data, but also the external children
+    reference lists, per field name.
+    Recall that externally stored fields are those marked "child_node" in
+    the protobuf definition.
+    This object must be treated as immutable, including its config data.
+    """
+
+    __slots__ = (
+        '_config',
+        '_children',
+        '_hash',
+        '_branch',
+        '__weakref__'
+    )
+
+    def __init__(self, branch, data, children=None):
+        self._branch = branch
+        self._config = ConfigDataRevision(data)
+        self._children = children
+        self._finalize()
+
+    def _finalize(self):
+        self._hash = self._hash_content()
+        if self._hash not in _rev_cache:
+            _rev_cache[self._hash] = self
+        if self._config._hash not in _rev_cache:
+            _rev_cache[self._config._hash] = self._config
+        else:
+            self._config = _rev_cache[self._config._hash]  # re-use!
+
+    def _hash_content(self):
+        # hash is derived from config hash and hashes of all children
+        m = md5('' if self._config is None else self._config._hash)
+        if self._children is not None:
+            for child_field in sorted(self._children.keys()):
+                children = self._children[child_field]
+                assert isinstance(children, list)
+                m.update(''.join(c._hash for c in children))
+        return m.hexdigest()[:12]
+
+    @property
+    def hash(self):
+        return self._hash
+
+    @property
+    def data(self):
+        return None if self._config is None else self._config.data
+
+    @property
+    def node(self):
+        return self._branch._node
+
+    @property
+    def type(self):
+        return self._config.data.__class__
+
+    def clear_hash(self):
+        self._hash = None
+
+    def get(self, depth):
+        """
+        Get config data of node. If depth > 0, recursively assemble the
+        branch nodes. If depth is < 0, this results in a fully exhaustive
+        "complete config".
+        """
+        orig_data = self._config.data
+        data = orig_data.__class__()
+        data.CopyFrom(orig_data)
+        if depth:
+            # collect children
+            cfields = children_fields(self.type).iteritems()
+            for field_name, field in cfields:
+                if field.is_container:
+                    for rev in self._children[field_name]:
+                        child_data = rev.get(depth=depth - 1)
+                        child_data_holder = getattr(data, field_name).add()
+                        child_data_holder.MergeFrom(child_data)
+                else:
+                    rev = self._children[field_name][0]
+                    child_data = rev.get(depth=depth - 1)
+                    child_data_holder = getattr(data, field_name)
+                    child_data_holder.MergeFrom(child_data)
+        return data
+
+    def update_data(self, data, branch):
+        """Return a NEW revision which is updated for the modified data"""
+        new_rev = copy(self)
+        new_rev._branch = branch
+        new_rev._config = self._config.__class__(data)
+        new_rev._finalize()
+        return new_rev
+
+    def update_children(self, name, children, branch):
+        """Return a NEW revision which is updated for the modified children"""
+        new_children = self._children.copy()
+        new_children[name] = children
+        new_rev = copy(self)
+        new_rev._branch = branch
+        new_rev._children = new_children
+        new_rev._finalize()
+        return new_rev
+
+    def update_all_children(self, children, branch):
+        """Return a NEW revision which is updated for all children entries"""
+        new_rev = copy(self)
+        new_rev._branch = branch
+        new_rev._children = children
+        new_rev._finalize()
+        return new_rev
diff --git a/python/core/config/config_rev_persisted.py b/python/core/config/config_rev_persisted.py
new file mode 100644
index 0000000..8b25b82
--- /dev/null
+++ b/python/core/config/config_rev_persisted.py
@@ -0,0 +1,143 @@
+#
+# 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.
+#
+
+"""
+A config rev object that persists itself
+"""
+from bz2 import compress, decompress
+
+import structlog
+from simplejson import dumps, loads
+
+from voltha.core.config.config_rev import ConfigRevision, children_fields
+
+log = structlog.get_logger()
+
+
+class PersistedConfigRevision(ConfigRevision):
+
+    compress = False
+
+    __slots__ = ('_kv_store',)
+
+    def __init__(self, branch, data, children=None):
+        self._kv_store = branch._node._root._kv_store
+        super(PersistedConfigRevision, self).__init__(branch, data, children)
+
+    def _finalize(self):
+        super(PersistedConfigRevision, self)._finalize()
+        self.store()
+
+    def __del__(self):
+        try:
+            if self._hash:
+                if self._config.__weakref__ is None:
+                    if self._config._hash in self._kv_store:
+                        del self._kv_store[self._config._hash]
+                assert self.__weakref__ is None
+                if self._hash in self._kv_store:
+                    del self._kv_store[self._hash]
+        except Exception, e:
+            # this should never happen
+            log.exception('del-error', hash=self.hash, e=e)
+
+    def store(self):
+
+        try:
+            # crude serialization of children hash and config data hash
+            if self._hash in self._kv_store:
+                return
+
+            self.store_config()
+
+            children_lists = {}
+            for field_name, children in self._children.iteritems():
+                hashes = [rev.hash for rev in children]
+                children_lists[field_name] = hashes
+
+            data = dict(
+                children=children_lists,
+                config=self._config._hash
+            )
+            blob = dumps(data)
+            if self.compress:
+                blob = compress(blob)
+
+            self._kv_store[self._hash] = blob
+
+        except Exception, e:
+            log.exception('store-error', e=e)
+
+    @classmethod
+    def load(cls, branch, kv_store, msg_cls, hash):
+        #  Update the branch's config store
+        blob = kv_store[hash]
+        if cls.compress:
+            blob = decompress(blob)
+        data = loads(blob)
+
+        config_hash = data['config']
+        config_data = cls.load_config(kv_store, msg_cls, config_hash)
+
+        children_list = data['children']
+        assembled_children = {}
+        node = branch._node
+        for field_name, meta in children_fields(msg_cls).iteritems():
+            child_msg_cls = tmp_cls_loader(meta.module, meta.type)
+            children = []
+            for child_hash in children_list[field_name]:
+                child_node = node._mknode(child_msg_cls)
+                child_node.load_latest(child_hash)
+                child_rev = child_node.latest
+                children.append(child_rev)
+            assembled_children[field_name] = children
+        rev = cls(branch, config_data, assembled_children)
+        return rev
+
+    def store_config(self):
+        if self._config._hash in self._kv_store:
+            return
+
+        # crude serialization of config data
+        blob = self._config._data.SerializeToString()
+        if self.compress:
+            blob = compress(blob)
+
+        self._kv_store[self._config._hash] = blob
+
+    @classmethod
+    def load_config(cls, kv_store, msg_cls, config_hash):
+        blob = kv_store[config_hash]
+        if cls.compress:
+            blob = decompress(blob)
+
+        # TODO use a loader later on
+        data = msg_cls()
+        data.ParseFromString(blob)
+        return data
+
+
+def tmp_cls_loader(module_name, cls_name):
+    # TODO this shall be generalized
+    from voltha.protos import voltha_pb2, health_pb2, adapter_pb2, \
+        logical_device_pb2, device_pb2, openflow_13_pb2, bbf_fiber_base_pb2, \
+        bbf_fiber_traffic_descriptor_profile_body_pb2, \
+        bbf_fiber_tcont_body_pb2, bbf_fiber_gemport_body_pb2, \
+        bbf_fiber_multicast_gemport_body_pb2, \
+        bbf_fiber_multicast_distribution_set_body_pb2, \
+        omci_mib_db_pb2, \
+        omci_alarm_db_pb2
+    return getattr(locals()[module_name], cls_name)
diff --git a/python/core/config/config_root.py b/python/core/config/config_root.py
new file mode 100644
index 0000000..4b1006d
--- /dev/null
+++ b/python/core/config/config_root.py
@@ -0,0 +1,229 @@
+#
+# 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.
+#
+from uuid import uuid4
+
+import structlog
+from simplejson import dumps, loads
+
+from voltha.core.config.config_node import ConfigNode
+from voltha.core.config.config_rev import ConfigRevision
+from voltha.core.config.config_rev_persisted import PersistedConfigRevision
+from voltha.core.config.merge_3way import MergeConflictException
+
+log = structlog.get_logger()
+
+
+class ConfigRoot(ConfigNode):
+
+    __slots__ = (
+        '_dirty_nodes',  # holds set of modified nodes per transaction branch
+        '_kv_store',
+        '_loading',
+        '_rev_cls',
+        '_deferred_callback_queue',
+        '_notification_deferred_callback_queue'
+    )
+
+    def __init__(self, initial_data, kv_store=None, rev_cls=ConfigRevision):
+        self._kv_store = kv_store
+        self._dirty_nodes = {}
+        self._loading = False
+        if kv_store is not None and \
+                not issubclass(rev_cls, PersistedConfigRevision):
+            rev_cls = PersistedConfigRevision
+        self._rev_cls = rev_cls
+        self._deferred_callback_queue = []
+        self._notification_deferred_callback_queue = []
+        super(ConfigRoot, self).__init__(self, initial_data, False)
+
+    @property
+    def kv_store(self):
+        if self._loading:
+            # provide fake store for storing things
+            # TODO this shall be a fake_dict providing noop for all relevant
+            # operations
+            return dict()
+        else:
+            return self._kv_store
+
+    def mkrev(self, *args, **kw):
+        return self._rev_cls(*args, **kw)
+
+    def mk_txbranch(self):
+        txid = uuid4().hex[:12]
+        self._dirty_nodes[txid] = {self}
+        self._mk_txbranch(txid)
+        return txid
+
+    def del_txbranch(self, txid):
+        for dirty_node in self._dirty_nodes[txid]:
+            dirty_node._del_txbranch(txid)
+        del self._dirty_nodes[txid]
+
+    def fold_txbranch(self, txid):
+        try:
+            self._merge_txbranch(txid, dry_run=1)
+        except MergeConflictException:
+            self.del_txbranch(txid)
+            raise
+
+        try:
+            self._merge_txbranch(txid)
+        finally:
+            self.execute_deferred_callbacks()
+
+    # ~~~~~~ Overridden, root-level CRUD methods to handle transactions ~~~~~~~
+
+    def update(self, path, data, strict=None, txid=None, mk_branch=None):
+        assert mk_branch is None
+        self.check_callback_queue()
+        try:
+            if txid is not None:
+                dirtied = self._dirty_nodes[txid]
+
+                def track_dirty(node):
+                    dirtied.add(node)
+                    return node._mk_txbranch(txid)
+
+                res = super(ConfigRoot, self).update(path, data, strict,
+                                                          txid, track_dirty)
+            else:
+                res = super(ConfigRoot, self).update(path, data, strict)
+        finally:
+            self.execute_deferred_callbacks()
+        return res
+
+    def add(self, path, data, txid=None, mk_branch=None):
+        assert mk_branch is None
+        self.check_callback_queue()
+        try:
+            if txid is not None:
+                dirtied = self._dirty_nodes[txid]
+
+                def track_dirty(node):
+                    dirtied.add(node)
+                    return node._mk_txbranch(txid)
+
+                res = super(ConfigRoot, self).add(path, data, txid, track_dirty)
+            else:
+                res = super(ConfigRoot, self).add(path, data)
+        finally:
+            self.execute_deferred_callbacks()
+        return res
+
+    def remove(self, path, txid=None, mk_branch=None):
+        assert mk_branch is None
+        self.check_callback_queue()
+        try:
+            if txid is not None:
+                dirtied = self._dirty_nodes[txid]
+
+                def track_dirty(node):
+                    dirtied.add(node)
+                    return node._mk_txbranch(txid)
+
+                res = super(ConfigRoot, self).remove(path, txid, track_dirty)
+            else:
+                res = super(ConfigRoot, self).remove(path)
+        finally:
+            self.execute_deferred_callbacks()
+        return res
+
+    def check_callback_queue(self):
+        assert len(self._deferred_callback_queue) == 0
+
+    def enqueue_callback(self, func, *args, **kw):
+        self._deferred_callback_queue.append((func, args, kw))
+
+    def enqueue_notification_callback(self, func, *args, **kw):
+        """
+        A separate queue is required for notification.  Previously, when the
+        notifications were added to the self._deferred_callback_queue there
+        was a deadlock condition where two callbacks were added (one
+        related to the model change and one for the notification related to
+        that model change).  Since the model change requires the
+        self._deferred_callback_queue to be empty then there was a deadlock
+        in that scenario.   The simple approach to avoid this problem is to
+        have separate queues for model and notification.
+        TODO: Investigate whether there is a need for the
+        self._deferred_callback_queue to handle multiple model events at the same time
+        :param func: callback function
+        :param args: args
+        :param kw: key-value args
+        :return: None
+        """
+        self._notification_deferred_callback_queue.append((func, args, kw))
+
+    def execute_deferred_callbacks(self):
+        # First process the model-triggered related callbacks
+        while self._deferred_callback_queue:
+            func, args, kw = self._deferred_callback_queue.pop(0)
+            func(*args, **kw)
+
+        # Execute the notification callbacks
+        while self._notification_deferred_callback_queue:
+            func, args, kw = self._notification_deferred_callback_queue.pop(0)
+            func(*args, **kw)
+
+
+    # ~~~~~~~~~~~~~~~~ Persistence related ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    @classmethod
+    def load(cls, root_msg_cls, kv_store):
+        # need to use fake kv store during initial load for not to override
+        # our real k vstore
+        fake_kv_store = dict()  # shall use more efficient mock dict
+        root = cls(root_msg_cls(), kv_store=fake_kv_store,
+                   rev_cls=PersistedConfigRevision)
+        # we can install the real store now
+        root._kv_store = kv_store
+        root.load_from_persistence(root_msg_cls)
+        return root
+
+    def _make_latest(self, branch, *args, **kw):
+        super(ConfigRoot, self)._make_latest(branch, *args, **kw)
+        # only persist the committed branch
+        if self._kv_store is not None and branch._txid is None:
+            root_data = dict(
+                latest=branch._latest._hash,
+                tags=dict((k, v._hash) for k, v in self._tags.iteritems())
+            )
+            blob = dumps(root_data)
+            self._kv_store['root'] = blob
+
+    def persist_tags(self):
+        if self._kv_store is not None:
+            root_data = loads(self.kv_store['root'])
+            root_data = dict(
+                latest=root_data['latest'],
+                tags=dict((k, v._hash) for k, v in self._tags.iteritems())
+            )
+            blob = dumps(root_data)
+            self._kv_store['root'] = blob
+
+    def load_from_persistence(self, root_msg_cls):
+        self._loading = True
+        blob = self._kv_store['root']
+        root_data = loads(blob)
+
+        for tag, hash in root_data['tags'].iteritems():
+            self.load_latest(hash)
+            self._tags[tag] = self.latest
+
+        self.load_latest(root_data['latest'])
+
+        self._loading = False
+
diff --git a/python/core/config/config_txn.py b/python/core/config/config_txn.py
new file mode 100644
index 0000000..87dfc59
--- /dev/null
+++ b/python/core/config/config_txn.py
@@ -0,0 +1,73 @@
+#
+# 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.
+#
+
+class ClosedTransactionError(Exception):
+    pass
+
+
+class ConfigTransaction(object):
+
+    __slots__ = (
+        '_proxy',
+        '_txid'
+    )
+
+    def __init__(self, proxy, txid):
+        self._proxy = proxy
+        self._txid = txid
+
+    def __del__(self):
+        if self._txid:
+            try:
+                self.cancel()
+            except:
+                raise
+
+    # ~~~~~~~~~~~~~~~~~~~~ CRUD ops within the transaction ~~~~~~~~~~~~~~~~~~~~
+
+    def get(self, path='/', depth=None, deep=None):
+        if self._txid is None:
+            raise ClosedTransactionError()
+        return self._proxy.get(path, depth=depth, deep=deep, txid=self._txid)
+
+    def update(self, path, data, strict=False):
+        if self._txid is None:
+            raise ClosedTransactionError()
+        return self._proxy.update(path, data, strict, self._txid)
+
+    def add(self, path, data):
+        if self._txid is None:
+            raise ClosedTransactionError()
+        return self._proxy.add(path, data, self._txid)
+
+    def remove(self, path):
+        if self._txid is None:
+            raise ClosedTransactionError()
+        return self._proxy.remove(path, self._txid)
+
+    # ~~~~~~~~~~~~~~~~~~~~ transaction finalization ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    def cancel(self):
+        """Explicitly cancel the transaction"""
+        self._proxy.cancel_transaction(self._txid)
+        self._txid = None
+
+    def commit(self):
+        """Commit all transaction changes"""
+        try:
+            self._proxy.commit_transaction(self._txid)
+        finally:
+            self._txid = None
diff --git a/python/core/config/merge_3way.py b/python/core/config/merge_3way.py
new file mode 100644
index 0000000..5444a6c
--- /dev/null
+++ b/python/core/config/merge_3way.py
@@ -0,0 +1,267 @@
+#
+# 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.
+#
+
+"""
+3-way merge function for config rev objects.
+"""
+from collections import OrderedDict
+from copy import copy
+
+from voltha.core.config.config_proxy import CallbackType, OperationContext
+from voltha.core.config.config_rev import children_fields
+
+
+class MergeConflictException(Exception):
+    pass
+
+
+def merge_3way(fork_rev, src_rev, dst_rev, merge_child_func, dry_run=False):
+    """
+    Attempt to merge src_rev into dst_rev but taking into account what have
+    changed in both revs since the last known common point, the fork_rev.
+    In case of conflict, raise a MergeConflictException(). If dry run is True,
+    don't actually perform the merge, but detect potential conflicts.
+
+    This function recurses into all children nodes stored under the rev and
+    performs the merge if the children is also part of a transaction branch.
+
+    :param fork_rev: Point of forking (last known common state between branches
+    :param src_rev: Latest rev from which we merge to dst_rev
+    :param dst_rev: Target (destination) rev
+    :param merge_child_fun: To run a potential merge in all children that
+    may need merge (determined from the local changes)
+    :param dry_run: If True, do not perform the merge, but detect merge
+    conflicts.
+    :return: The new dst_rev (a new rev instance) the list of changes that
+    occurred in this node or any of its children as part of this merge.
+    """
+
+    # to collect change tuples of (<callback-type>, <op-context>)
+    changes = []
+
+    class AnalyzeChanges(object):
+        def __init__(self, lst1, lst2, keyname):
+            self.keymap1 = OrderedDict((getattr(rev._config._data, keyname), i)
+                                       for i, rev in enumerate(lst1))
+            self.keymap2 = OrderedDict((getattr(rev._config._data, keyname), i)
+                                       for i, rev in enumerate(lst2))
+            self.added_keys = [
+                k for k in self.keymap2.iterkeys() if k not in self.keymap1]
+            self.removed_keys = [
+                k for k in self.keymap1.iterkeys() if k not in self.keymap2]
+            self.changed_keys = [
+                k for k in self.keymap1.iterkeys()
+                if k in self.keymap2 and
+                    lst1[self.keymap1[k]]._hash != lst2[self.keymap2[k]]._hash
+            ]
+
+    # Note: there are a couple of special cases that can be optimized
+    # for larer on. But since premature optimization is a bad idea, we
+    # defer them.
+
+    # deal with config data first
+    if dst_rev._config is fork_rev._config:
+        # no change in master, accept src if different
+        config_changed = dst_rev._config != src_rev._config
+    else:
+        if dst_rev._config.hash != src_rev._config.hash:
+            raise MergeConflictException('Config collision')
+        config_changed = True
+
+    # now to the external children fields
+    new_children = dst_rev._children.copy()
+    _children_fields = children_fields(fork_rev.data.__class__)
+
+    for field_name, field in _children_fields.iteritems():
+
+        fork_list = fork_rev._children[field_name]
+        src_list = src_rev._children[field_name]
+        dst_list = dst_rev._children[field_name]
+
+        if dst_list == src_list:
+            # we do not need to change the dst, however we still need
+            # to complete the branch purging in child nodes so not
+            # to leave dangling branches around
+            [merge_child_func(rev) for rev in src_list]
+            continue
+
+        if not field.key:
+            # If the list is not keyed, we really should not merge. We merely
+            # check for collision, i.e., if both changed (and not same)
+            if dst_list == fork_list:
+                # dst branch did not change since fork
+
+                assert src_list != fork_list, 'We should not be here otherwise'
+
+                # the incoming (src) rev changed, and we have to apply it
+                new_children[field_name] = [
+                    merge_child_func(rev) for rev in src_list]
+
+                if field.is_container:
+                    changes.append((CallbackType.POST_LISTCHANGE,
+                                    OperationContext(field_name=field_name)))
+
+            else:
+                if src_list != fork_list:
+                    raise MergeConflictException(
+                        'Cannot merge because single child node or un-keyed'
+                        'children list has changed')
+
+        else:
+
+            if dst_list == fork_list:
+                # Destination did not change
+
+                # We need to analyze only the changes on the incoming rev
+                # since fork
+                src = AnalyzeChanges(fork_list, src_list, field.key)
+
+                new_list = copy(src_list)  # we start from the source list
+
+                for key in src.added_keys:
+                    idx = src.keymap2[key]
+                    new_rev = merge_child_func(new_list[idx])
+                    new_list[idx] = new_rev
+                    changes.append(
+                        (CallbackType.POST_ADD,
+                         new_rev.data))
+                         # OperationContext(
+                         #     field_name=field_name,
+                         #     child_key=key,
+                         #     data=new_rev.data)))
+
+                for key in src.removed_keys:
+                    old_rev = fork_list[src.keymap1[key]]
+                    changes.append((
+                        CallbackType.POST_REMOVE,
+                        old_rev.data))
+                        # OperationContext(
+                        #     field_name=field_name,
+                        #     child_key=key,
+                        #     data=old_rev.data)))
+
+                for key in src.changed_keys:
+                    idx = src.keymap2[key]
+                    new_rev = merge_child_func(new_list[idx])
+                    new_list[idx] = new_rev
+                    # updated child gets its own change event
+
+                new_children[field_name] = new_list
+
+            else:
+
+                # For keyed fields we can really investigate what has been
+                # added, removed, or changed in both branches and do a
+                # fine-grained collision detection and merge
+
+                src = AnalyzeChanges(fork_list, src_list, field.key)
+                dst = AnalyzeChanges(fork_list, dst_list, field.key)
+
+                new_list = copy(dst_list)  # this time we start with the dst
+
+                for key in src.added_keys:
+                    # we cannot add if it has been added and is different
+                    if key in dst.added_keys:
+                        # it has been added to both, we need to check if
+                        # they are the same
+                        child_dst_rev = dst_list[dst.keymap2[key]]
+                        child_src_rev = src_list[src.keymap2[key]]
+                        if child_dst_rev.hash == child_src_rev.hash:
+                            # they match, so we do not need to change the
+                            # dst list, but we still need to purge the src
+                            # branch
+                            merge_child_func(child_dst_rev)
+                        else:
+                            raise MergeConflictException(
+                                'Cannot add because it has been added and '
+                                'different'
+                            )
+                    else:
+                        # this is a brand new key, need to add it
+                        new_rev = merge_child_func(src_list[src.keymap2[key]])
+                        new_list.append(new_rev)
+                        changes.append((
+                            CallbackType.POST_ADD,
+                            new_rev.data))
+                            # OperationContext(
+                            #     field_name=field_name,
+                            #     child_key=key,
+                            #     data=new_rev.data)))
+
+                for key in src.changed_keys:
+                    # we cannot change if it was removed in dst
+                    if key in dst.removed_keys:
+                        raise MergeConflictException(
+                            'Cannot change because it has been removed')
+
+                    # if it changed in dst as well, we need to check if they
+                    # match (same change
+                    elif key in dst.changed_keys:
+                        child_dst_rev = dst_list[dst.keymap2[key]]
+                        child_src_rev = src_list[src.keymap2[key]]
+                        if child_dst_rev.hash == child_src_rev.hash:
+                            # they match, so we do not need to change the
+                            # dst list, but we still need to purge the src
+                            # branch
+                            merge_child_func(child_src_rev)
+                        elif child_dst_rev._config.hash != child_src_rev._config.hash:
+                            raise MergeConflictException(
+                                'Cannot update because it has been changed and '
+                                'different'
+                            )
+                        else:
+                            new_rev = merge_child_func(
+                                src_list[src.keymap2[key]])
+                            new_list[dst.keymap2[key]] = new_rev
+                            # no announcement for child update
+
+                    else:
+                        # it only changed in src branch
+                        new_rev = merge_child_func(src_list[src.keymap2[key]])
+                        new_list[dst.keymap2[key]] = new_rev
+                        # no announcement for child update
+
+                for key in reversed(src.removed_keys):  # we go from highest
+                                                        # index to lowest
+
+                    # we cannot remove if it has changed in dst
+                    if key in dst.changed_keys:
+                        raise MergeConflictException(
+                            'Cannot remove because it has changed')
+
+                    # if it has not been removed yet from dst, then remove it
+                    if key not in dst.removed_keys:
+                        dst_idx = dst.keymap2[key]
+                        old_rev = new_list.pop(dst_idx)
+                        changes.append((
+                            CallbackType.POST_REMOVE,
+                            old_rev.data))
+                            # OperationContext(
+                            #     field_name=field_name,
+                            #     child_key=key,
+                            #     data=old_rev.data)))
+
+                new_children[field_name] = new_list
+
+    if not dry_run:
+        rev = src_rev if config_changed else dst_rev
+        rev = rev.update_all_children(new_children, dst_rev._branch)
+        if config_changed:
+            changes.append((CallbackType.POST_UPDATE, rev.data))
+        return rev, changes
+
+    else:
+        return None, None