He said the Coalition's policy was a miserable failure and will mean millions of Australians will not have high speed internet connections.

"I can't find a dumber piece of public policy than buying the copper off Telstra," he said after inspecting optic fibre being laid for the NBN at Gungahlin in northern Canberra.

"I mean, come on down, Alan Bond. Kerry Packer would be laughing all the way to the bank if he found a mug willing to buy Telstra's copper network."

Under Telstra's current agreement with NBN Co, the copper network will progressively be retired as NBN Co's fibre optic cable is rolled out.

Senator Conroy accused Coalition communications spokesman Malcolm Turnbull of displaying ignorance about how the needs of broadband would evolve.

"Customers using the NBN are also connecting more devices to the NBN and this is where Malcolm Turnbull and their version of a broadband network fails miserably," he said.

"If you understand broadband, if you understand that it is being used for more applications that require more bandwidth every single day, then you know that Malcolm Turnbull's network is a fail.

"Malcolm Turnbull is going to build a one-lane Sydney Harbour Bridge because he says he can do it cheaper and faster."

Senator Conroy said the Telstra copper network was old and decaying and would not be able to deliver the internet speeds proposed by Mr Turnbull.

"The speeds he is going to claim today are defying the laws of physics and the quality of the copper in the ground," Senator Conroy said.