diff --git a/apns.py b/apns.py
index fdcec08..463cbe7 100644
--- a/apns.py
+++ b/apns.py
@@ -24,7 +24,9 @@
 # SOFTWARE.
 
 from binascii import a2b_hex, b2a_hex
-from datetime import datetime
+from datetime import datetime, timedelta
+from time import mktime
+from random import getrandbits
 from socket import socket, AF_INET, SOCK_STREAM
 from struct import pack, unpack
 
@@ -142,7 +144,7 @@ def write(self, string):
 
 
 class PayloadAlert(object):
-    def __init__(self, body, action_loc_key=None, loc_key=None,
+    def __init__(self, body=None, action_loc_key=None, loc_key=None,
                  loc_args=None, launch_image=None):
         super(PayloadAlert, self).__init__()
         self.body = body
@@ -152,7 +154,9 @@ def __init__(self, body, action_loc_key=None, loc_key=None,
         self.launch_image = launch_image
 
     def dict(self):
-        d = { 'body': self.body }
+        d = {}
+        if self.body:
+            d['body'] = self.body
         if self.action_loc_key:
             d['action-loc-key'] = self.action_loc_key
         if self.loc_key:
@@ -263,6 +267,30 @@ def items(self):
                     # some more data and append to buffer
                     break
 
+class UnknownResponse(Exception):
+    def __init__(self):
+        super(UnknownResponse, self).__init__()
+
+class UnknownError(Exception):
+    def __init__(self):
+        super(UnknownError, self).__init__()
+
+class ProcessingError(Exception):
+    def __init__(self):
+        super(ProcessingError, self).__init__()
+
+class InvalidTokenSizeError(Exception):
+    def __init__(self):
+        super(InvalidTokenSizeError, self).__init__()
+
+class InvalidPayloadSizeError(Exception):
+    def __init__(self):
+        super(InvalidPayloadSizeError, self).__init__()
+
+class InvalidTokenError(Exception):
+    def __init__(self):
+        super(InvalidTokenError, self).__init__()
+
 class GatewayConnection(APNsConnection):
     """
     A class that represents a connection to the APNs gateway server
@@ -274,21 +302,44 @@ def __init__(self, use_sandbox=False, **kwargs):
             'gateway.sandbox.push.apple.com')[use_sandbox]
         self.port = 2195
 
-    def _get_notification(self, token_hex, payload):
+    def _get_notification(self, token_hex, payload, identifier, expiry):
         """
         Takes a token as a hex string and a payload as a Python dict and sends
         the notification
         """
+        identifier_bin = identifier[:4]
+        expiry_bin = APNs.packed_uint_big_endian(int(mktime(expiry.timetuple())))
         token_bin = a2b_hex(token_hex)
         token_length_bin = APNs.packed_ushort_big_endian(len(token_bin))
         payload_json = payload.json()
         payload_length_bin = APNs.packed_ushort_big_endian(len(payload_json))
 
-        notification = ('\0' + token_length_bin + token_bin
+        notification = ('\x01' + identifier_bin + expiry_bin + token_length_bin + token_bin
             + payload_length_bin + payload_json)
 
         return notification
 
-    def send_notification(self, token_hex, payload):
-        self.write(self._get_notification(token_hex, payload))
+    def send_notification(self, token_hex, payload, expiry=None):
+        if expiry is None:
+            expiry = datetime.now() + timedelta(30)
+        
+        identifier = pack('>I', getrandbits(32))
+        self.write(self._get_notification(token_hex, payload, identifier, expiry))
+        
+        error_response = self.read(6)
+        if error_response != '':
+            command = error_response[0]
+            status = ord(error_response[1])
+            response_identifier = error_response[2:6]
+            
+            if command != '\x08' or response_identifier != identifier:
+                raise UnknownResponse()
+            
+            if status == 0:
+                return
+            
+            raise {1: ProcessingError,
+                   5: InvalidTokenSizeError,
+                   7: InvalidPayloadSizeError,
+                   8: InvalidTokenError}.get(status, UnknownError)()
 
diff --git a/tests.py b/tests.py
index ff5af97..e1962f2 100644
--- a/tests.py
+++ b/tests.py
@@ -3,6 +3,7 @@
 from apns import *
 from binascii import a2b_hex
 from random import random
+from datetime import datetime
 
 import hashlib
 import os
@@ -77,10 +78,14 @@ def testGatewayServer(self):
             sound = "default",
             badge = 4
         )
-        notification = gateway_server._get_notification(token_hex, payload)
+        identifier = 'abcd'
+        expiry = datetime(2000, 01, 01, 00, 00, 00)
+        notification = gateway_server._get_notification(token_hex, payload, identifier, expiry)
 
         expected_length = (
-            1                       # leading null byte
+            1                       # leading command byte
+            + 4                     # Identifier as a 4 bytes buffer
+            + 4                     # Expiry timestamp as a packed integer
             + 2                     # length of token as a packed short
             + len(token_hex) / 2    # length of token as binary string
             + 2                     # length of payload as a packed short
@@ -88,7 +93,7 @@ def testGatewayServer(self):
         )
 
         self.assertEqual(len(notification), expected_length)
-        self.assertEqual(notification[0], '\0')
+        self.assertEqual(notification[0], '\x01') # Enhanched format command byte
 
     def testFeedbackServer(self):
         pem_file = TEST_CERTIFICATE