NBN Co classifies an MDU as a premise where two or more homes joined by a common wall or property boundary and managed by a body corporate, with MDUs making up around one-third of premises to receive the NBN via fibre.

Steffens told the hearing this can include a block of town houses. For example, a set of 10 town houses could potentially be labelled an MDU.

The committee was also told that in situations where an apartment building's body corporate does not agree to an NBN connection and declared "frustrated", NBN Co will move on.

"If the body corporate doesn't agree, we will obviously try and convince them to accept the installation. If ultimately the body corporate says no, we declare the building frustrated and move on..." said Mike Quigley, chief executive at NBN Co.

"We anticipate not a large number of MDUs to be declared frustrated. We think most body corporates would say 'this is a good thing -- go ahead and install it'. Now we may have some -- we expect there will be some..."