Optus' Krishnapillai added that despite the telco's desire for volume discounts from NBN Co, it was difficult to gauge what volumes of carriage would be needed to justify such a discount.

"That is the real difficulty as I don't know that volume per se should be criterion or effectively some kind of discount," he said. "The key [criterion in the bill] is how you define 'aiding efficiency'.

There is no definition around that so I don't know that there is a number [for a volume discount]."

Optus interconnect and economic regulation general manager, Andrew Sheridan, said for volume discounts to apply, NBN Co would need to demonstrate that at a certain volume of carriage the economics of supply changed.

"It is not reasonable to say that if we had several times the volume of company X we should get a discount of X per cent," he said.