Both setups ensure competition for the backhaul but leave "last mile" infrastructure the responsibility of the incumbent carrier.
In the United States, the Telecommunications Act of 1996 added a number of provisions designed to increase competition.
Unbundled access is defined as "The duty to provide, to any requesting telecommunications carrier for the provision of a telecommunications service, nondiscriminatory access to network elements on an unbundled basis at any technically feasible point on rates, terms, and conditions that are just, reasonable, and nondiscriminatory in accordance with the terms and conditions of the agreement and the requirements of this section and section 252.
[1] In 2005, after much litigation concerning its original unbundling rules, the Federal Communications Commission (FCC) made the decision to limit the number and types of unbundled elements that telecommunications carriers were required to offer competitors under the common carrier laws outlined in 47 U.S.C §§ 251.
A just and reasonable rate is determined on a nondiscriminatory basis and is based on cost of providing the interconnection or unbundled network element.