from datetime import datetime


def time_duration(time_start, time_end):
    """
    This function is used to calculate the time difference in seconds.
    :param time_start: The start time represented by a string.
    :param time_end: The end time represented by a string.
    :return: The time difference in seconds, integer representation.
    """
    datetime_object1 = datetime.strptime(time_start, '%H:%M:%S')
    datetime_object2 = datetime.strptime(time_end, '%H:%M:%S')
    return (datetime_object2 - datetime_object1).total_seconds()