diff --git a/stack/mtp_base.py b/mtp_device/mtp_base.py
similarity index 98%
rename from stack/mtp_base.py
rename to mtp_device/mtp_base.py
index 2f323f9..810dded 100644
--- a/stack/mtp_base.py
+++ b/mtp_device/mtp_base.py
@@ -21,7 +21,7 @@ def __init__(self, info):
         self.info = info
 
     def get_handles(self):
-        return [self]
+        return [self.get_uid()]
 
     def get_uid(self):
         return self.uid
diff --git a/mtp_device/mtp_device.py b/mtp_device/mtp_device.py
new file mode 100644
index 0000000..ebaa822
--- /dev/null
+++ b/mtp_device/mtp_device.py
@@ -0,0 +1,282 @@
+from mtp_base import MtpObjectContainer, MtpEntityInfoInterface
+from mtp_proto import MU16, MU32, MStr, MArray, OperationDataCodes, ResponseCodes, mtp_data
+from struct import unpack
+
+
+class MtpProtocolException(Exception):
+
+    def __init__(self, response, msg=None):
+        super(MtpProtocolException, self).__init__(msg)
+        self.response = response
+
+
+operations = {}
+
+
+def operation(opcode, num_params=None, session_required=True):
+    '''
+    Decorator for an API operation function
+
+    :param opcode: operation code
+    :param num_params: number of parameter the operation expects (default: None)
+    :param session_required: is the operation requires a session (default: True)
+    '''
+
+    def decorator(func):
+
+        def wrapper(self, request, response):
+            try:
+                if num_params is not None:
+                    if request.num_params() < num_params:
+                        raise MtpProtocolException(ResponseCodes.PARAMETER_NOT_SUPPORTED)
+                if session_required and (self.session_id is None):
+                    raise MtpProtocolException(ResponseCodes.SESSION_NOT_OPEN)
+                res = func(self, request)
+            except MtpProtocolException as ex:
+                response.status = ex.response
+                res = None
+            return res
+
+        if opcode in operations:
+            raise Exception('operation %#x already defined', opcode)
+        operations[opcode] = wrapper
+        return wrapper
+
+    return decorator
+
+
+class MtpRequest(object):
+
+    def __init__(self, tid, code, params):
+        self.tid = tid
+        self.code = code
+        self.params = params
+
+    def num_params(self):
+        return len(self.params)
+
+    def get_param(self, idx):
+        if idx < len(self.params):
+            return self.params[idx]
+        return None
+
+    @classmethod
+    def from_buff(cls, data):
+        if len(data) % 4 != 0:
+            raise Exception('request length (%#x) is not a multiple of four' % (len(data)))
+        if len(data) < 0xc:
+            raise Exception('request too short')
+        length, ctype, opcode, tid = unpack('<IBBI', data[:0xc])
+        if len(data) != length:
+            raise Exception('request length (%#x) != actual length (%#x)' % (length, len(data)))
+        params_buff = data[0xc:]
+        params = []
+        for i in range(0, len(params_buff), 4):
+            params.append(unpack('<I', params_buff[i:i + 4])[0])
+        return MtpRequest(tid, opcode, params)
+
+
+class MtpResponse(object):
+
+    def __init__(self, request):
+        self.request = request
+        self.status = ResponseCodes.OK
+        self.data = None
+
+
+class MtpDevice(MtpObjectContainer):
+
+    def __init__(self, info):
+        super(MtpDevice, self).__init__(info)
+        self.stores = {}
+        self.operations = operations
+        self.info.operations_supported = operations.keys()
+        self.session_id = None
+
+    def add_storage(self, storage):
+        '''
+        :type storage: MtpStorage
+        :param storage: storage to add
+        '''
+        self.stores[storage.get_uid()] = storage
+        storage.set_device(self)
+
+    @operation(OperationDataCodes.GetDeviceInfo, num_params=0, session_required=False)
+    def GetDeviceInfo(self, request):
+        return mtp_data(request, self.get_info())
+
+    # @operation(OperationDataCodes., num_params=None, session_required=True)
+    @operation(OperationDataCodes.OpenSession, num_params=1, session_required=False)
+    def OpenSession(self, request):
+        if self.session_id:
+            raise MtpProtocolException(ResponseCodes.SESSION_ALREADY_OPEN)
+        self.session_id = request.params[0]
+
+    @operation(OperationDataCodes.CloseSession, num_params=0)
+    def CloseSession(self, request):
+        self.session_id = None
+
+    @operation(OperationDataCodes.GetStorageIDs, num_params=0)
+    def GetStorageIDs(self, request):
+        ids = self.stores.keys()
+        data = MArray(MU32, ids)
+        return mtp_data(request, data)
+
+    @operation(OperationDataCodes.GetStorageInfo, num_params=1)
+    def GetStorageInfo(self, request):
+        storage_id = request.get_param(0)
+        storage = self.get_storage(storage_id)
+        return mtp_data(request, storage.get_info())
+
+    @operation(OperationDataCodes.GetNumObjects, num_params=1)
+    def GetNumObjects(self, request):
+        storage_id = request.get_param(0)
+        if storage_id == 0xffffffff:
+            relevant_store = self.stores.values()
+        else:
+            relevant_store = [self.get_storage(storage_id)]
+        obj_fmt_code = request.get_param(1)
+        handles = self.get_handles_from_stores(relevant_store, obj_fmt_code)
+        # .. todo:: assoc_handle filtering
+        # assoc_handle = request.get_param(2)
+        return mtp_data(request, MU32(len(handles)))
+
+    @operation(OperationDataCodes.GetObjectHandles, num_params=1)
+    def GetObjectHandles(self, request):
+        storage_id = request.get_param(0)
+        if storage_id == 0xffffffff:
+            relevant_store = self.stores.values()
+        else:
+            relevant_store = [self.get_storage(storage_id)]
+        obj_fmt_code = request.get_param(1)
+        handles = self.get_handles_from_stores(relevant_store, obj_fmt_code)
+        # .. todo:: assoc_handle filtering
+        # assoc_handle = request.get_param(2)
+        return mtp_data(request, MArray(MU32, handles))
+
+    @operation(OperationDataCodes.GetObjectInfo, num_params=1)
+    def GetObjectInfo(self, request):
+        handle = request.get_param(0)
+        obj = self.get_object(handle)
+        return mtp_data(request, obj.get_info())
+
+    @operation(OperationDataCodes.GetObject, num_params=1)
+    def GetObject(self, request):
+        handle = request.get_param(0)
+        obj = self.get_object(handle)
+        return mtp_data(request, obj.data)
+
+    # @operation(OperationDataCodes.GetThumb, num_params=1)
+    # def GetThumb(self, request):
+
+    def get_handles_from_stores(self, stores, obj_fmt_code):
+        '''
+        :param stores: stores to search in
+        :param obj_fmt_code: format to filter objects by
+        :return: list of handles
+        '''
+        res = []
+        for store in stores:
+            handles = store.get_handles()
+            if obj_fmt_code:
+                handles = [h for h in handles if store.get_object(h).get_fmt() == obj_fmt_code]
+            res.extend(handles)
+        return res
+
+    def get_object(self, handle):
+        '''
+        :param handle: handle of the object
+        :raises: MtpProtocolException if there is no object with given handle
+        :return: MtpObject
+        '''
+        obj = None
+        for store in self.stores.values():
+            obj = store.get_object(handle)
+            if obj:
+                break
+        if not obj:
+            raise MtpProtocolException(ResponseCodes.INVALID_OBJECT_HANDLE)
+        return obj
+
+    def get_storage(self, storage_id):
+        '''
+        :param storage_id: the storage id to get
+        :raises: MtpProtocolException if storage with this id does not exist
+        :return: MtpStorage
+        '''
+        if storage_id not in self.stores:
+            raise MtpProtocolException(ResponseCodes.INVALID_STORAGE_ID)
+        return self.stores[storage_id]
+
+
+class MtpDeviceInfo(MtpEntityInfoInterface):
+
+    def __init__(
+        self,
+        std_version, mtp_vendor_ext_id, mtp_version, mtp_extensions,
+        functional_mode, operations_supported, events_supported,
+        device_properties_supported, capture_formats, playback_formats,
+        manufacturer, model, device_version, serial_number
+    ):
+        '''
+        :type std_version: 16bit uint
+        :param std_version: Standard Version
+        :type mtp_vendor_ext_id: 32bit uint
+        :param mtp_vendor_ext_id: MTP Vendor Extension ID
+        :type mtp_version: 16bit uint
+        :param mtp_version: MTP Version
+        :type mtp_extensions: str
+        :param mtp_extensions: MTP Extensions
+        :type functional_mode: 16bit uint
+        :param functional_mode: Functional Mode
+        :type operations_supported: list of 16bit uint
+        :param operations_supported: Operations Supported
+        :type events_supported: list of 16bit uint
+        :param events_supported: Events Supported
+        :type device_properties_supported: list of 16bit uint
+        :param device_properties_supported: Device Properties Supported
+        :type capture_formats: list of 16bit uint
+        :param capture_formats: Capture Formats
+        :type playback_formats: list of 16bit uint
+        :param playback_formats: Playback Formats
+        :type manufacturer: str
+        :param manufacturer: Manufacturer
+        :type model: str
+        :param model: Model
+        :type device_version: str
+        :param device_version: Device Version
+        :type serial_number: str
+        :param serial_number: Serial Number
+        '''
+        self.std_version = std_version
+        self.mtp_vendor_ext_id = mtp_vendor_ext_id
+        self.mtp_version = mtp_version
+        self.mtp_extensions = mtp_extensions
+        self.functional_mode = functional_mode
+        self.operations_supported = operations_supported
+        self.events_supported = events_supported
+        self.device_properties_supported = device_properties_supported
+        self.capture_formats = capture_formats
+        self.playback_formats = playback_formats
+        self.manufacturer = manufacturer
+        self.model = model
+        self.device_version = device_version
+        self.serial_number = serial_number
+
+    def pack(self):
+        return (
+            MU16(self.std_version) +
+            MU32(self.mtp_vendor_ext_id) +
+            MU16(self.mtp_version) +
+            MStr(self.mtp_extensions) +
+            MU16(self.functional_mode) +
+            MArray(MU16, self.operations_supported) +
+            MArray(MU16, self.events_supported) +
+            MArray(MU16, self.device_properties_supported) +
+            MArray(MU16, self.capture_formats) +
+            MArray(MU16, self.playback_formats) +
+            MStr(self.manufacturer) +
+            MStr(self.model) +
+            MStr(self.device_version) +
+            MStr(self.serial_number)
+        )
diff --git a/stack/mtp_object.py b/mtp_device/mtp_object.py
similarity index 96%
rename from stack/mtp_object.py
rename to mtp_device/mtp_object.py
index 3cb16dc..a597cdd 100644
--- a/stack/mtp_object.py
+++ b/mtp_device/mtp_object.py
@@ -2,12 +2,12 @@
 The object's binary data, the ObjectInfo dataset,
 Object Properties and Object References
 '''
-from mtp_base import MtpEntity, MtpEntityInfoInterface
+from mtp_base import MtpObjectContainer, MtpEntityInfoInterface
 from mtp_proto import MU32, MU16, MStr, MDateTime
 import os
 
 
-class MtpObject(MtpEntity):
+class MtpObject(MtpObjectContainer):
 
     def __init__(self, data, info, properties, references):
         super(MtpObject, self).__init__(info)
@@ -41,7 +41,8 @@ def from_fs_recursive(cls, path):
     def from_file(cls, path):
         # TODO: handle cases othe than regular file here ...
         if os.path.isfile(path):
-            data = open(path, 'rb').read()
+            with open(path, 'rb') as f:
+                data = f.read()
         else:
             data = b''
         filename = os.path.split(path)[-1]
diff --git a/stack/mtp_proto.py b/mtp_device/mtp_proto.py
similarity index 91%
rename from stack/mtp_proto.py
rename to mtp_device/mtp_proto.py
index 973d822..ff818f5 100644
--- a/stack/mtp_proto.py
+++ b/mtp_device/mtp_proto.py
@@ -1,4 +1,3 @@
-from enum import IntEnum
 from struct import pack, unpack
 import datetime
 
@@ -201,4 +200,17 @@ def MS64(i):
 
 
 def MU64(i):
-    return pack('<Q', i)
\ No newline at end of file
+    return pack('<Q', i)
+
+
+def mtp_response(container, status):
+    tid = 0 if not container else container.tid
+    return MU32(0xC) + MU16(ContainerTypes.Response) + MU16(status) + MU32(tid)
+
+
+def mtp_error(container, status):
+    return (None, mtp_response(container, status))
+
+
+def mtp_data(container, data):
+    return MU32(len(data) + 0xC) + MU16(ContainerTypes.Data) + MU16(container.code) + MU32(container.tid) + data
diff --git a/stack/mtp_storage.py b/mtp_device/mtp_storage.py
similarity index 89%
rename from stack/mtp_storage.py
rename to mtp_device/mtp_storage.py
index b26b5c3..b266ab5 100644
--- a/stack/mtp_storage.py
+++ b/mtp_device/mtp_storage.py
@@ -15,6 +15,12 @@ def add_object(self, obj):
     def set_device(self, dev):
         self.dev = dev
 
+    def get_handles(self):
+        handles = super(MtpObjectContainer, self).get_handles()
+        for obj in self.objects:
+            handles.extend(obj.get_handles())
+        return handles
+
 
 class MtpStorageInfo(MtpEntityInfoInterface):
 
diff --git a/stack/mtp_device.py b/stack/mtp_device.py
deleted file mode 100644
index 887fe57..0000000
--- a/stack/mtp_device.py
+++ /dev/null
@@ -1,137 +0,0 @@
-from mtp_base import MtpObjectContainer, MtpEntityInfoInterface
-from mtp_proto import MU16, MU32, MStr, MArray, OperationDataCodes
-
-operations = {}
-
-
-def operation(opcode):
-    def decorator(func):
-        def wrapper(*args, **kwargs):
-            res = func(*args, **kwargs)
-            return res
-        if opcode in operations:
-            raise Exception('operation %#x already defined', opcode)
-        operations[opcode] = wrapper
-        return wrapper
-    return decorator
-
-
-class MtpDevice(MtpObjectContainer):
-
-    def __init__(self, info):
-        super(MtpDevice, self).__init__(info)
-        self.storages = {}
-        self.operations = operations
-
-    def add_storage(self, storage):
-        '''
-        :type storage: MtpStorage
-        :param storage: storage to add
-        '''
-        self.storages[storage.get_uid()] = storage
-        storage.set_device(self)
-
-    @operation(OperationDataCodes.GetDeviceInfo)
-    def GetDeviceInfo(self):
-        return self.get_info()
-
-
-class MtpDeviceInfo(MtpEntityInfoInterface):
-
-    def __init__(
-        self,
-        std_version, mtp_vendor_ext_id, mtp_version, mtp_extensions,
-        functional_mode, operations_supported, events_supported,
-        device_properties_supported, capture_formats, playback_formats,
-        manufacturer, model, device_version, serial_number
-    ):
-        '''
-        :type std_version: 16bit uint
-        :param std_version: Standard Version
-        :type mtp_vendor_ext_id: 32bit uint
-        :param mtp_vendor_ext_id: MTP Vendor Extension ID
-        :type mtp_version: 16bit uint
-        :param mtp_version: MTP Version
-        :type mtp_extensions: str
-        :param mtp_extensions: MTP Extensions
-        :type functional_mode: 16bit uint
-        :param functional_mode: Functional Mode
-        :type operations_supported: list of 16bit uint
-        :param operations_supported: Operations Supported
-        :type events_supported: list of 16bit uint
-        :param events_supported: Events Supported
-        :type device_properties_supported: list of 16bit uint
-        :param device_properties_supported: Device Properties Supported
-        :type capture_formats: list of 16bit uint
-        :param capture_formats: Capture Formats
-        :type playback_formats: list of 16bit uint
-        :param playback_formats: Playback Formats
-        :type manufacturer: str
-        :param manufacturer: Manufacturer
-        :type model: str
-        :param model: Model
-        :type device_version: str
-        :param device_version: Device Version
-        :type serial_number: str
-        :param serial_number: Serial Number
-        '''
-        self.std_version = std_version
-        self.mtp_vendor_ext_id = mtp_vendor_ext_id
-        self.mtp_version = mtp_version
-        self.mtp_extensions = mtp_extensions
-        self.functional_mode = functional_mode
-        self.operations_supported = operations_supported
-        self.events_supported = events_supported
-        self.device_properties_supported = device_properties_supported
-        self.capture_formats = capture_formats
-        self.playback_formats = playback_formats
-        self.manufacturer = manufacturer
-        self.model = model
-        self.device_version = device_version
-        self.serial_number = serial_number
-
-    def pack(self):
-        return (
-            MU16(self.std_version) +
-            MU32(self.mtp_vendor_ext_id) +
-            MU16(self.mtp_version) +
-            MStr(self.mtp_extensions) +
-            MU16(self.functional_mode) +
-            MArray(MU16, self.operations_supported) +
-            MArray(MU16, self.events_supported) +
-            MArray(MU16, self.device_properties_supported) +
-            MArray(MU16, self.capture_formats) +
-            MArray(MU16, self.playback_formats) +
-            MStr(self.manufacturer) +
-            MStr(self.model) +
-            MStr(self.device_version) +
-            MStr(self.serial_number)
-        )
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-