diff --git a/coapthon/client/coap.py b/coapthon/client/coap.py
index f199b2c..5a3747c 100644
--- a/coapthon/client/coap.py
+++ b/coapthon/client/coap.py
@@ -65,6 +65,13 @@ class CoAP(object):
 
         self._receiver_thread = None
 
+    def purge_transactions(self, timeout_time=defines.EXCHANGE_LIFETIME):
+        """
+        Clean old transactions
+
+        """
+        self._messageLayer.purge(timeout_time)
+
     def close(self):
         """
         Stop the client.
@@ -96,16 +103,21 @@ class CoAP(object):
         assert isinstance(c, int)
         self._currentMID = c
 
-    def send_message(self, message):
+    def send_message(self, message, no_response=False):
         """
         Prepare a message to send on the UDP socket. Eventually set retransmissions.
 
         :param message: the message to send
+        :param no_response: whether to await a response from the request
         """
         if isinstance(message, Request):
             request = self._requestLayer.send_request(message)
             request = self._observeLayer.send_request(request)
             request = self._blockLayer.send_request(request)
+            if no_response:
+                # don't add the send message to the message layer transactions
+                self.send_datagram(request)
+                return
             transaction = self._messageLayer.send_request(request)
             self.send_datagram(transaction.request)
             if transaction.request.type == defines.Types["CON"]:
@@ -238,7 +250,7 @@ class CoAP(object):
         while not self.stopped.isSet():
             self._socket.settimeout(0.1)
             try:
-                datagram, addr = self._socket.recvfrom(1152)
+                datagram, addr = self._socket.recvfrom(1500)
             except socket.timeout:  # pragma: no cover
                 continue
             except Exception as e:  # pragma: no cover
diff --git a/coapthon/client/helperclient.py b/coapthon/client/helperclient.py
index d204b68..eb79191 100644
--- a/coapthon/client/helperclient.py
+++ b/coapthon/client/helperclient.py
@@ -223,17 +223,26 @@ class HelperClient(object):
         :param request: the request to send
         :param callback: the callback function to invoke upon response
         :param timeout: the timeout of the request
+        :param no_response: whether to await a response from the request
         :return: the response
         """
         if callback is not None:
             thread = threading.Thread(target=self._thread_body, args=(request, callback))
             thread.start()
         else:
-            self.protocol.send_message(request)
+            self.protocol.send_message(request, no_response=no_response)
             if no_response:
                 return
             try:
-                response = self.queue.get(block=True, timeout=timeout)
+                while True:
+                    response = self.queue.get(block=True, timeout=timeout)
+                    if response is not None:
+                        if response.mid == request.mid:
+                            return response
+                        if response.type == defines.Types["NON"]:
+                            return response
+                    else:
+                        return response
             except Empty:
                 #if timeout is set
                 response = None
diff --git a/coapthon/defines.py b/coapthon/defines.py
index 09fff43..172d058 100644
--- a/coapthon/defines.py
+++ b/coapthon/defines.py
@@ -125,7 +125,7 @@ class OptionRegistry(object):
     LOCATION_QUERY = OptionItem(20,"Location-Query",STRING,  True, None)
     BLOCK2 =        OptionItem(23, "Block2",        INTEGER, False, None)
     BLOCK1 =        OptionItem(27, "Block1",        INTEGER, False, None)
-    SIZE2 =         OptionItem(28, "Size2",         INTEGER, False, None)
+    SIZE2 =         OptionItem(28, "Size2",         INTEGER, False, 0)
     PROXY_URI =     OptionItem(35, "Proxy-Uri",     STRING,  False, None)
     PROXY_SCHEME =  OptionItem(39, "Proxy-Schema",  STRING,  False, None)
     SIZE1 =         OptionItem(60, "Size1",         INTEGER, False, None)
diff --git a/coapthon/layers/blocklayer.py b/coapthon/layers/blocklayer.py
index dd96142..cc7bec1 100644
--- a/coapthon/layers/blocklayer.py
+++ b/coapthon/layers/blocklayer.py
@@ -60,7 +60,7 @@ class BlockLayer(object):
                 del transaction.request.block2
             else:
                 # early negotiation
-                byte = 0
+                byte = num * size
                 self._block2_receive[key_token] = BlockItem(byte, num, m, size)
                 del transaction.request.block2
 
@@ -233,6 +233,7 @@ class BlockLayer(object):
 
                 self._block2_receive[key_token] = BlockItem(byte, num, m, size)
 
+                
             # correct m
             m = 0 if ((num * size) + size) > len(transaction.response.payload) else 1
             # add size2 if requested or if payload is bigger than one datagram
@@ -240,6 +241,7 @@ class BlockLayer(object):
             if (transaction.request.size2 is not None and transaction.request.size2 == 0) or \
                (transaction.response.payload is not None and len(transaction.response.payload) > defines.MAX_PAYLOAD):
                 transaction.response.size2 = len(transaction.response.payload)
+
             transaction.response.payload = transaction.response.payload[byte:byte + size]
             del transaction.response.block2
             transaction.response.block2 = (num, m, size)
diff --git a/coapthon/layers/forwardLayer.py b/coapthon/layers/forwardLayer.py
index 22f521a..b7363f2 100644
--- a/coapthon/layers/forwardLayer.py
+++ b/coapthon/layers/forwardLayer.py
@@ -53,11 +53,12 @@ class ForwardLayer(object):
         :rtype : Transaction
         :return: the edited transaction
         """
+        wkc_resource_is_defined = defines.DISCOVERY_URL in self._server.root
         path = str("/" + transaction.request.uri_path)
         transaction.response = Response()
         transaction.response.destination = transaction.request.source
         transaction.response.token = transaction.request.token
-        if path == defines.DISCOVERY_URL:
+        if path == defines.DISCOVERY_URL and not wkc_resource_is_defined:
             transaction = self._server.resourceLayer.discover(transaction)
         else:
             new = False
diff --git a/coapthon/layers/messagelayer.py b/coapthon/layers/messagelayer.py
index c46ea96..966a5f7 100644
--- a/coapthon/layers/messagelayer.py
+++ b/coapthon/layers/messagelayer.py
@@ -42,17 +42,17 @@ class MessageLayer(object):
         self._current_mid %= 65535
         return current_mid
 
-    def purge(self):
+    def purge(self, timeout_time=defines.EXCHANGE_LIFETIME):
         for k in list(self._transactions.keys()):
             now = time.time()
             transaction = self._transactions[k]
-            if transaction.timestamp + defines.EXCHANGE_LIFETIME < now:
+            if transaction.timestamp + timeout_time < now:
                 logger.debug("Delete transaction")
                 del self._transactions[k]
         for k in list(self._transactions_token.keys()):
             now = time.time()
             transaction = self._transactions_token[k]
-            if transaction.timestamp + defines.EXCHANGE_LIFETIME < now:
+            if transaction.timestamp + timeout_time < now:
                 logger.debug("Delete transaction")
                 del self._transactions_token[k]
 
diff --git a/coapthon/layers/requestlayer.py b/coapthon/layers/requestlayer.py
index 0286b4c..e864436 100644
--- a/coapthon/layers/requestlayer.py
+++ b/coapthon/layers/requestlayer.py
@@ -52,11 +52,12 @@ class RequestLayer(object):
         :rtype : Transaction
         :return: the edited transaction with the response to the request
         """
+        wkc_resource_is_defined = defines.DISCOVERY_URL in self._server.root
         path = str("/" + transaction.request.uri_path)
         transaction.response = Response()
         transaction.response.destination = transaction.request.source
         transaction.response.token = transaction.request.token
-        if path == defines.DISCOVERY_URL:
+        if path == defines.DISCOVERY_URL and not wkc_resource_is_defined:
             transaction = self._server.resourceLayer.discover(transaction)
         else:
             try:
diff --git a/coapthon/messages/message.py b/coapthon/messages/message.py
index 6364bf8..98e4a76 100644
--- a/coapthon/messages/message.py
+++ b/coapthon/messages/message.py
@@ -119,17 +119,16 @@ class Message(object):
         """
         Set the Token of the message.
 
-        :type value: String
+        :type value: Bytes
         :param value: the Token
         :raise AttributeError: if value is longer than 256
         """
         if value is None:
             self._token = value
             return
-        if isinstance(value, int):
-            value = bytes([value])
         if not isinstance(value, bytes):
-            value = bytes(value, "utf-8")
+            value = bytes(value)
+
         if len(value) > 256:
             raise AttributeError
         self._token = value
@@ -646,8 +645,7 @@ class Message(object):
         Delete the Block2 option.
         """
         self.del_option_by_number(defines.OptionRegistry.BLOCK2.number)
-
-    @property
+        
     def size1(self):
         value = None
         for option in self.options:
@@ -668,14 +666,24 @@ class Message(object):
 
     @property
     def size2(self):
+        """
+        Get the Size2 option.
+
+        :return: the Size2 value
+        """
         value = None
         for option in self.options:
             if option.number == defines.OptionRegistry.SIZE2.number:
-                value = option.value if option.value is not None else 0
+                value = option.value 
         return value
 
     @size2.setter
     def size2(self, value):
+        """
+        Set the Size2 option.
+
+        :param value: the Block2 value
+        """
         option = Option()
         option.number = defines.OptionRegistry.SIZE2.number
         option.value = value
@@ -683,6 +691,9 @@ class Message(object):
 
     @size2.deleter
     def size2(self):
+        """
+        Delete the Size2 option.
+        """
         self.del_option_by_number(defines.OptionRegistry.SIZE2.number)
 
     @property
diff --git a/coapthon/serializer.py b/coapthon/serializer.py
index a92726f..2f4683f 100644
--- a/coapthon/serializer.py
+++ b/coapthon/serializer.py
@@ -129,6 +129,9 @@ class Serializer(object):
             return defines.Codes.BAD_REQUEST.number
         except struct.error:
             return defines.Codes.BAD_REQUEST.number
+        except UnicodeDecodeError as e:
+            logger.debug(e)
+            return defines.Codes.BAD_REQUEST.number
 
     @staticmethod
     def serialize(message):
@@ -154,10 +157,8 @@ class Serializer(object):
         values = [tmp, message.code, message.mid]
 
         if message.token is not None and tkl > 0:
-
-            for b in message.token:
-                fmt += "B"
-                values.append(b)
+            fmt += "%ss" % tkl
+            values.append(message.token)
 
         options = Serializer.as_sorted_list(message.options)  # already sorted
         lastoptionnumber = 0
diff --git a/coapthon/utils.py b/coapthon/utils.py
index dd99122..20948e4 100644
--- a/coapthon/utils.py
+++ b/coapthon/utils.py
@@ -201,3 +201,6 @@ class Tree(object):
 
     def __delitem__(self, key):
         del self.tree[key]
+
+    def __contains__(self, item):
+        return item in self.tree
diff --git a/exampleresources.py b/exampleresources.py
index 0330829..d98a89b 100644
--- a/exampleresources.py
+++ b/exampleresources.py
@@ -1,3 +1,5 @@
+#!/usr/bin/env python
+
 import time
 from coapthon import defines