def fiber_type(val):
    """ 
    decode fiber type 
    REF: http://www.ciscopress.com/articles/article.asp?p=170740&seqNum=7
    """
    if val == 651:
        fstr = 'G.651 (50um core multimode)'
    elif val == 652:
        fstr = 'G.652 (standard SMF)'
    elif val == 653:
        fstr = 'G.653 (dispersion-shifted fiber)'
    elif val == 654:
        fstr = 'G.654 (1550nm loss-minimzed fiber)'
    elif val == 655:
        fstr = 'G.655 (nonzero dispersion-shifted fiber)'
    else:
        fstr = '%d (unknown)' % val
    return fstr
