def is_valid(line):
    """
    Check whether given line has valid format
    :param line: checked line(string)
    :return: True if valid, false otherwise
    """
    return ('tcpwinsize' not in line
            or (line['tcpwinsize'].isdigit() and line['tcpttl'].isdigit() and line['tcpsynsize'].isdigit())
            or (line['tcpwinsize'] == 'N/A' and line['tcpttl'] == 'N/A' and line['tcpsynsize'] == 'N/A'))