<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def join(self, master):
 """Join this speaker to another "master" speaker."""

        self.avTransport.SetAVTransportURI([
            ('InstanceID', 0),
            ('CurrentURI', 'x-rincon:{0}'.format(master.uid)),
            ('CurrentURIMetaData', '')
        ])
        self._zgs_cache.clear()
        self._parse_zone_group_state()