diff --git a/sylk/applications/webrtcgateway/janus.py b/sylk/applications/webrtcgateway/janus.py
index d7801c0..9404237 100644
--- a/sylk/applications/webrtcgateway/janus.py
+++ b/sylk/applications/webrtcgateway/janus.py
@@ -1,260 +1,263 @@
 
 import json
 import uuid
 
 from application.notification import IObserver, NotificationCenter, NotificationData
 from application.python import Null
 from application.python.types import Singleton
 from autobahn.twisted.websocket import connectWS, WebSocketClientFactory, WebSocketClientProtocol
 from twisted.internet import reactor, defer
 from twisted.internet.protocol import ReconnectingClientFactory
 from twisted.python.failure import Failure
 from zope.interface import implements
 
 from sylk import __version__ as SYLK_VERSION
 from sylk.applications.webrtcgateway.configuration import JanusConfig
 from sylk.applications.webrtcgateway.logger import log
 
 
 class Request(object):
-    def __init__(self, request_type, **kwargs):
+    def __init__(self, request_type, **kw):
         self.janus = request_type
         self.transaction = uuid.uuid4().hex
         if JanusConfig.api_secret:
             self.apisecret = JanusConfig.api_secret
-        self.__dict__.update(**kwargs)
+        conflicting_keywords = set(self.__dict__).intersection(kw)
+        if conflicting_keywords:
+            raise KeyError('request specified keyword arguments that are already in use: {}'.format(', '.join(sorted(conflicting_keywords))))
+        self.__dict__.update(**kw)
 
     @property
     def type(self):
         return self.janus
 
     @property
     def transaction_id(self):
         return self.transaction
 
     def as_dict(self):
         return self.__dict__.copy()
 
 
 class JanusError(Exception):
     def __init__(self, code, reason):
         super(JanusError, self).__init__(reason)
         self.code = code
         self.reason = reason
 
 
 class JanusClientProtocol(WebSocketClientProtocol):
     _event_handlers = None
     _pending_transactions = None
     _keepalive_timers = None
     _keepalive_interval = 45
 
     notification_center = NotificationCenter()
 
     def onOpen(self):
         self.notification_center.post_notification('JanusBackendConnected', sender=self)
         self._pending_transactions = {}
         self._keepalive_timers = {}
         self._event_handlers = {}
 
     def onMessage(self, payload, isBinary):
         if isBinary:
             log.warn('Unexpected binary payload received')
             return
         self.notification_center.post_notification('WebRTCJanusTrace', sender=self, data=NotificationData(direction='INCOMING', message=payload, peer=self.peer))
         try:
             data = json.loads(payload)
         except Exception as e:
             log.warn('Error decoding payload: %s' % e)
             return
         try:
             message_type = data.pop('janus')
         except KeyError:
             log.warn('Received payload lacks message type: %s' % payload)
             return
         transaction_id = data.pop('transaction', None)
         if message_type == 'event' or transaction_id is None:
             # This is an event. Janus is not very consistent here, some 'events'
             # do have the transaction id set. So we check for the message type as well.
             handle_id = data.pop('sender', -1)
             handler = self._event_handlers.get(handle_id, Null)
             try:
                 handler(handle_id, message_type, data)
             except Exception:
                 log.exception()
             return
         try:
             request, deferred = self._pending_transactions.pop(transaction_id)
         except KeyError:
             log.warn('Discarding unexpected response: %s' % payload)
             return
         # events were handled above, so the only message types we get here are ack, success and error
         # todo: some plugin errors are delivered with message_type == 'success' and the error code is buried somewhere in plugindata
         if message_type == 'error':
             code = data['error']['code']
             reason = data['error']['reason']
             deferred.errback(JanusError(code, reason))
         elif message_type == 'ack':
             deferred.callback(None)
         else:  # success
             # keepalive and trickle only receive an ACK, thus are handled above in message_type == 'ack', not here
             if request.type in ('create', 'attach'):
                 result = data['data']['id']
             elif request.type in ('destroy', 'detach'):
                 result = None
             else:  # info, message (for synchronous message requests only)
                 result = data
             deferred.callback(result)
 
     def connectionLost(self, reason):
         super(JanusClientProtocol, self).connectionLost(reason)
         self.notification_center.post_notification('JanusBackendDisconnected', sender=self, data=NotificationData(reason=reason.getErrorMessage()))
 
     def disconnect(self, code=1000, reason=u''):
         self.sendClose(code, reason)
 
     def _send_request(self, request):
         deferred = defer.Deferred()
         data = json.dumps(request.as_dict())
         if request.type != 'keepalive' and 'session_id' in data:  # postpone keepalive messages as long as we have non-keepalive traffic for a given session
             keepalive_timer = self._keepalive_timers.get(request.session_id, Null)
             keepalive_timer.reset(self._keepalive_interval)
         self.notification_center.post_notification('WebRTCJanusTrace', sender=self, data=NotificationData(direction='OUTGOING', message=data, peer=self.peer))
         self.sendMessage(data)
         self._pending_transactions[request.transaction_id] = (request, deferred)
         return deferred
 
     def _start_keepalive(self, session_id):
         self._keepalive_timers[session_id] = reactor.callLater(self._keepalive_interval, self._send_keepalive, session_id)
 
     def _stop_keepalive(self, session_id):
         timer = self._keepalive_timers.pop(session_id, Null)
         timer.cancel()
 
     def _send_keepalive(self, session_id):
         deferred = self._send_request(Request('keepalive', session_id=session_id))
         deferred.addBoth(self._keepalive_callback, session_id)
 
     def _keepalive_callback(self, result, session_id):
         if isinstance(result, Failure):
             self._keepalive_timers.pop(session_id)
         else:
             self._keepalive_timers[session_id] = reactor.callLater(self._keepalive_interval, self._send_keepalive, session_id)
 
     # Public API
 
     def set_event_handler(self, handle_id, event_handler):
         if event_handler is None:
             self._event_handlers.pop(handle_id, None)
         else:
             assert callable(event_handler)
             self._event_handlers[handle_id] = event_handler
 
     def info(self):
         return self._send_request(Request('info'))
 
     def create_session(self):
         return self._send_request(Request('create')).addCallback(self._start_keepalive)
 
     def destroy_session(self, session_id):
         self._stop_keepalive(session_id)
         return self._send_request(Request('destroy', session_id=session_id))
 
     def attach(self, session_id, plugin):
         return self._send_request(Request('attach', session_id=session_id, plugin=plugin))
 
     def detach(self, session_id, handle_id):
         return self._send_request(Request('detach', session_id=session_id, handle_id=handle_id))
 
     def message(self, session_id, handle_id, body, jsep=None):
         extra_kw = {} if jsep is None else {'jsep': jsep}
         return self._send_request(Request('message', session_id=session_id, handle_id=handle_id, body=body, **extra_kw))
 
     def trickle(self, session_id, handle_id, candidates):
         if candidates:
             candidates_kw = {'candidate': candidates[0]} if len(candidates) == 1 else {'candidates': candidates}  # todo: why handle single candidate differently?
         else:
             candidates_kw = {'candidate': {'completed': True}}
         return self._send_request(Request('trickle', session_id=session_id, handle_id=handle_id, **candidates_kw))
 
 
 class JanusClientFactory(ReconnectingClientFactory, WebSocketClientFactory):
     noisy = False
     protocol = JanusClientProtocol
 
 
 class JanusBackend(object):
     __metaclass__ = Singleton
 
     implements(IObserver)
 
     def __init__(self):
         self.factory = JanusClientFactory(url=JanusConfig.api_url, protocols=['janus-protocol'], useragent='SylkServer/%s' % SYLK_VERSION)
         self.connector = None
         self.protocol = Null
         self._stopped = False
 
     @property
     def ready(self):
         return self.protocol is not Null
 
     def start(self):
         notification_center = NotificationCenter()
         notification_center.add_observer(self, name='JanusBackendConnected')
         notification_center.add_observer(self, name='JanusBackendDisconnected')
         self.connector = connectWS(self.factory)
 
     def stop(self):
         if self._stopped:
             return
         self._stopped = True
         self.factory.stopTrying()
         notification_center = NotificationCenter()
         notification_center.discard_observer(self, name='JanusBackendConnected')
         notification_center.discard_observer(self, name='JanusBackendDisconnected')
         if self.connector is not None:
             self.connector.disconnect()
             self.connector = None
         if self.protocol is not None:
             self.protocol.disconnect()
             self.protocol = Null
 
     def set_event_handler(self, handle_id, event_handler):
         self.protocol.set_event_handler(handle_id, event_handler)
 
     def info(self):
         return self.protocol.info()
 
     def create_session(self):
         return self.protocol.create_session()
 
     def destroy_session(self, session_id):
         return self.protocol.destroy_session(session_id)
 
     def attach(self, session_id, plugin):
         return self.protocol.attach(session_id, plugin)
 
     def detach(self, session_id, handle_id):
         return self.protocol.detach(session_id, handle_id)
 
     def message(self, session_id, handle_id, body, jsep=None):
         return self.protocol.message(session_id, handle_id, body, jsep)
 
     def trickle(self, session_id, handle_id, candidates):
         return self.protocol.trickle(session_id, handle_id, candidates)
 
     # Notification handling
 
     def handle_notification(self, notification):
         handler = getattr(self, '_NH_%s' % notification.name, Null)
         handler(notification)
 
     def _NH_JanusBackendConnected(self, notification):
         assert self.protocol is Null
         self.protocol = notification.sender
         log.info('Janus backend connection up')
         self.factory.resetDelay()
 
     def _NH_JanusBackendDisconnected(self, notification):
         log.info('Janus backend connection down: %s' % notification.data.reason)
         self.protocol = Null