Australia's largest cities may receive no broadband upgrade until 2017 under the Coalition's current NBN policy, because households already have access to cable networks installed in the 1990s.
Cabled suburbs have a "pretty good service now", according to the opposition's communications spokesman, Malcolm Turnbull, and would be a lower priority than suburbs without any cable access.
The cables were installed to carry pay TV services but have since also provided broadband connections.
Hybrid fibre-coaxial [HFC] cable networks installed by Telstra to deliver Foxtel, Optus and some smaller operators cover most of Melbourne, Sydney and Brisbane, parts of inner Darwin, Perth, Adelaide and the Gold Coast, and regional towns of Geelong, Mildura and Ballarat in Victoria.
"Our current plan is to roll out fibre-to-the-node in all the fixed-line footprint. You can assume that we are going to build over the HFC [network] – it is just not a matter of priority," Mr Turnbull told Fairfax Media.
"As to what happens to the HFC areas longer term, that is going to depend on the negotiations with Telstra and Optus, so there are a few options there."
The Coalition would delay fibre-to-the-node upgrades in cable areas until the 2017-18 financial year, according to its policy paper. This contrasts with Labor's current NBN policy, which has already started building fibre-to-the-home connections in areas served by cable, with a view to replacing all fixed connections at 93 per cent of premises by 2021.
With cable networks already capable of delivering broadband speeds in the Coalition's target of 50 megabits per second [Mbps], it is unknown if these suburbs would ever receive an upgrade under a Coalition government.
Mr Turnbull said he had not yet achieved a "meeting of the minds" with Telstra about its cable network and future upgrades would depend on "relative costs". European research has found it possible to upgrade cable beyond 1 gigabit per second, but at high costs, according to a report by Dutch consulting firm TNO.
"I am satisfied that we can acquire the d-side copper [sites between households and exchanges], but there are a number of options [for HFC]. We could simply take it over and integrate it into the NBN, that is probably the cleanest option."
On Wednesday Mr Turnbull said: “On the one hand, you have 30 per cent of Australia that has access to 100 Mbps speeds. On the other hand, there are 2 million households that can’t even access a YouTube video because their connectivity is so poor. We make no bones that alleviating this digital divide is the most urgent priority of the Coalition’s broadband policy.”
Asked earlier whether he had already started negotiating with Telstra for the Coalition's NBN rollout, Mr Turnbull replied: "I could not possibly comment".
Both Telstra and Optus' cable networks cover about 2.5 million premises with cable, but have significant overlap. Carriers do not publish detailed maps of their cable networks, making it difficult for voters to know what kind of broadband connection they would get under a Coalition government.
Many cables have received upgrades since 2010 to support peak speeds of 100 Mbps. A recent study in the Netherlands found cable could be upgraded further to deliver download speeds of 1.6 gigabits per second, with uploads of 250 Mbps, but only for a maximum of 20 premises per section of cable.
Both Optus and Telstra have signed commercial agreements with NBN Co to decommission their cable for a fee, but Telstra's deal allows it to keep the cable active for Foxtel transmission. These contracts must be renegotiated if a Coalition government wants to keep the networks alive.
"The fact that both operators are keen to close down their networks indicates that they most certainly don't see these networks as ideal infrastructure for the future," telecommunications analyst Paul Budde said.
Upgrading the cable and changing regulations so all carriers could sell services would "require long [financial] negotiations and lengthy regulatory processes", he added.
"If it was all that easy that would have been done 10 years ago."
Known HFC coverage:
Telstra: Urban areas in Melbourne, Sydney, Brisbane, Gold Coast, Adelaide and Perth
Optus: Sydney, Melbourne and Brisbane
Other: Mildura, Ballarat, Bendigo, Albury-Wodonga, Canberra, Darwin and Perth (Ellenbrook)