http://www.oecd.org/dataoecd/26/6/27767944.pdf page 8.
The Economics of Regulation Principles and Institutions Vol 1 (1970) page 20.

Section 5 “Telecommunication Cost Calculations And Second Best Pricing” by Steve G. Parsons, “Laffont  and Tirole’s Competition In Telecommunications: A View From the US”, Int. J. of Economics of Business, Vol. 9, No.3 (2002) pp. 419-436

Petition no. 286/2007, by a judgement dated 31.03.09; Set Discovery Pvt. Ltd v. TRAI [Appeal10/07, by judgement dated 15.01.09]