Enlarge / A Frontier Communications van. (credit: Getty Images | jetcityimage)

As Frontier Communications moves closer to an expected bankruptcy filing, the ISP told investors that its troubles stem largely from its failure to invest properly in upgrading DSL to fiber broadband.

The presentation for investors, which is included in a Securities and Exchange Commission filing, said that “significant under-investment in fiber deployment and limited enterprise product offerings have created headwinds that the company is repositioning itself to reverse.” Much of Frontier’s fiber deployment was actually installed by Verizon before Verizon sold some of its operations to Frontier.

About 51 percent of Frontier revenue comes directly from residential consumers, with the rest mostly from wholesale and business customers. Frontier said the residential segment that provides most of its revenue “has the highest monthly churn,” meaning that customers are leaving the company in large numbers. DSL-customer losses are expected to increase, Frontier said.