NBN Co chief Ziggy Switkowski has admitted it will be ‘‘tough’’ to meet the federal government’s 2016 delivery deadline for the national broadband network, confirming the advice the company issued in preparation for the incoming government.

The coalition has promised to deliver 25 megabits per second (Mbps) broadband services to all homes by 2016 in its "affordable, cheaper, sooner " fibre-to-the-node NBN model.

Black screen: Senator Stephen Conroy and the monitor for the failed video link for Senator Scott Ludlam. Senator Lundlam continued to ask questions of NBN Co chief Dr Ziggy Switkowski via phone. Credit:Alex Ellinghausen

However, Dr Switkowski played down the deadline during a Senate committee hearing on the NBN in Canberra on Friday, saying the next calendar year would be one of stabilisation and transition.