NBN Co boss Mike Quigley says the rollout of the National Broadband Network (NBN) remains on schedule as it gathers speed in new housing estates.

Mr Quigley says the builder of the $37.4 billion high-speed network is on track to pass 286,000 homes and businesses by June 2013 as stated in its corporate plan released in August.

"The committee can be assured that we're on track to hit the corporate plan number, I'm prepared to back that," Mr Quigley told a joint parliamentary hearing in Canberra on Tuesday.

NBN Co chief operating officer Ralph Steffens said the NBN's designs had been slowed down as it had to update inaccurate data on pits and ducts in the Telstra network.

"Telstra is well under way in remediating the infrastructure to make it usable for us," Mr Steffens said.