def startStopDeviceGroup(self, deviceGroupObjList='all', action='start'):
        """
        Description
            Start one or more Device Groups and all its protocols.

        Parameters
            deviceGroupObj: <str>|<list>: 'all' or a list of Device Group objects.
                             Ex: ['/api/v1/sessions/1/ixnetwork/topology/1/deviceGroup/1']

            action: <str>: 'start'|'stop'
        """
        if deviceGroupObjList == 'all':
            queryData = {'from': '/',
                         'nodes': [{'node': 'topology', 'properties': [], 'where': []},
                                   {'node': 'deviceGroup', 'properties': ['href'], 'where': []}]
                        }

            queryResponse = self.ixnObj.query(data=queryData)
            try:
                topologyGroupList = queryResponse.json()['result'][0]['topology']
            except IndexError:
                raise IxNetRestApiException('\nNo Device  Group objects  found')

            deviceGroupObjList = []
            for dg in topologyGroupList:
                for dgHref in  dg['deviceGroup']:
                    deviceGroupObjList.append(dgHref['href'])

        url = self.ixnObj.sessionUrl+'/topology/deviceGroup/operations/%s' % action
        response = self.ixnObj.post(url, data={'arg1': deviceGroupObjList})
        self.ixnObj.waitForComplete(response, url+'/'+response.json()['id'])
        time.sleep(3)