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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def parse_transmission_id(header, reference_id=None):
 """\ Returns the transmission ID of the cable. If no transmission identifier was found, ``None`` is returned. `header` The cable's header `reference_id` The cable's reference ID. """

    m = _TID_PATTERN.search(header)
    if not m:
        return None
    return m.group(1)