@classmethod
def tcp(klass, host, port, interval, timeout=None, deregister=None):
    """
        Attempt to establish a tcp connection to the specified *host* and
        *port* at a specified *interval* with optional *timeout* and optional
        *deregister* after which a failing service will be automatically
        deregistered.
        """
    ret = {'tcp': '{host:s}:{port:d}'.format(host=host, port=port),
        'interval': interval}
    if timeout:
        ret['timeout'] = timeout
    if deregister:
        ret['DeregisterCriticalServiceAfter'] = deregister
    return ret
