The backup network, linking Sydney, Melbourne and Hobart, was reportedly finalised in a deal two months ago.
It will provide redundant capacity for Basslink's network management functions in the event of a primary network failure, according to general manager Michael Coates.
Telstra will benefit because it is the only other backhaul provider on the route under Bass Strait - and will therefore be the Hobart-Melbourne link in Internode's backup network.
Internode told iTnews earlier this week it anticipated cuts of up to 75 per cent in its use of Telstra backhaul services to and from Tasmania.
It would now appear unlikely further cuts are possible given the arrangements with Basslink and Internode's own redundant path requirements.
But just as unlikely is that Telstra's gains from being part of the Basslink back-up plan will offset its potential losses as ISPs cut back on buying as much wholesale capacity from that same Telstra backhaul pipe.
"Any telecommunications network needs a backup [source] completely off its zone," Coates told iTnews.
"Network management operates on our network first, then if our network has an issue we'd use the backup network [for our network management data]. The Hobart link is in essence Telstra but the whole solution is provided by Internode."
The backup network is for Basslink's own network management redundancy only; it will not be used to re-route customer traffic in the event of a failure, Coates said.
The latter will be largely taken care of by redundancy in the cable itself as well as by the provision of twin terrestrial paths at either end of the cable that link it into the respective capital cities.
Coates said that negotiations with one of the Victorian terrestrial link providers was proving "problematic", but he was hopeful a resolution would be found when he returns to Melbourne later this week.
The issues won't impact the cable launch date set for the first half of this year, he said.
"The worst case scenario is we launch on a slightly reduced redundancy [on the Victorian side] with one path running to Melbourne by the end of the first half [of 2009]," Coates said
"The other path might not yet by fully active but we'll still launch the cable on time. The perception that it's not going to be operational full stop is wrong."
He did not foresee similar problems with terrestrial providers on the Tasmanian side. "You'd have to be pretty surprised if Tasmania was holding things up," he said.
Coates also responded to criticism levelled at Basslink over the "slippage" of launch guidance from the end of April by what amounts to a couple of months at most.
He produced a timeline graph to delegates of the CommsDay Summit that showed the relatively recent introduction of the Basslink Telecoms business compared to the core electricity transmission business and demonstrated the short time-to-market in which the fibre cable has been deployed.
"The whole telecommunications operation of Basslink is very much in its infancy relative to the steps taken to get the power interconnector into the water," Coates said.
"The assumption that Basslink could have just flipped a switch [to turn on the fibre shows] a lack of understanding."
Coates said he believed the impending launch of the cable would result in strong residential DSL take-up in Tasmania.
"Tasmania is going to come up roaring," he predicted.
"What's going to be slower is take-up in the larger corporate market. It's really going to be SMBs and SMEs that embrace the technology in Tasmania."
Internode this week became the first ISP customer of Basslink. Other ISPs are expected to ink wholesale agreements with Basslink shortly.
Coates said Basslink had not negotiated any contra deals on access pricing with Internode in return for the provision of out-of-band network management capacity.