For your reference i am attaching the few more links which might help you.
http://www.thefoa.org/tech/lossbudg.htm
http://www.broadbandproperties.com/2007issues/jun07issues/corning_june.pdf
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0ahUKEwi14oa-86fLAhVBbY4KHWrmAWYQFgg1MAU&url=http%3A%2F%2Fresearch.ijcaonline.org%2Fvolume92%2Fnumber6%2Fpxc3895050.pdf&usg=AFQjCNH8rt