NBN Co's trials for fibre to the basement (FttB), or fibre to the building, have already been deemed a blistering success by Communications Minister Malcolm Turnbull , but documents released by NBN Co show the full plans for three-month FttB trials in a number of locations.

The trial, first announced by NBN Co late last year, is one option that the government is considering to potentially reduce the cost of the construction for the network, and speed up the rollout. The fibre-to-the-basement model would see multi-dwelling units such as apartments have the National Broadband Network (NBN) fibre pulled into the basement of their building, but VDSL services would be delivered over the existing copper line to each premises.

Such a technology would see NBN Co potentially quickly reduce the number of premises that have been passed by the network, but cannot currently order a service.

Turnbull's initial trial saw only one premises connected, but the company is now seeking to connect up to 10 office blocks or apartment buildings in order to connect up to 1,000 premises.

The document (PDF) released yesterday, first spotted by NBN blogger jxeeno, states that NBN Co will be performing tests in a limited number of locations around Australia for three months, unless the company decides to extend the test or it is terminated earlier than expected.

NBN Co said in the document that once the test is completed, the company may continue to offer services through the FttB product until a commercial service is available. The pilot is open to retailers who have signed a wholesale broadband agreement.

NBN Co and the retailer must both agree on the test customers taking part in the trial, and NBN Co is responsible for installing a splitter in the premises that will be inserted into a wall socket with a data line and a voice line. NBN Co will also connect an approved ADSL or VDSL2 modem in the premises for the test of the service.

The conditions of the agreement state that NBN Co "will have no liability for crosstalk at a pilot site caused by, or contributed to by, the FttB pilot". The participant in the trial is also not allowed to make any claim on crosstalk in relation to the pilot, NBN Co said.

Crosstalk over the copper line degrades the quality of the service on VDSL, but the government has said it would eventually explore the use of vectoring to reduce the crosstalk and improve broadband speeds on VDSL. Telstra and Alcatel-Lucent have already begun testing vectored VDSL .

The trial will not be used to connect up services such as medical or security alarms, NBN Co also stated.

It comes as the latest statistics for the NBN released yesterday show that as of January 19, the fibre network has passed 283,527 brownfields premises and 79,477 greenfields premises. A total of 84,731 of the brownfields premises still cannot order a service. There are currently 85,192 active customers on the fibre network.

Concern has been raised on the company's continued construction of the NBN now under the Coalition, however. Although Turnbull has committed to honouring NBN construction contracts through this year, the latest updates on where construction has commenced reveal that NBN Co is currently only constructing the network in four brownfields locations.

ZDNet has sought clarification from NBN Co on whether construction is expected to ramp up after the Australia Day long weekend.