Digital Subscriber Line service was built on the same lines that carried your traditional telephone service. Telephone and Internet were long treated as inseparable, but enterprising companies found that the copper wires could carry Internet signals without being connected to the phone network. Though contentious, this "dry loop" or "naked" DSL eliminates the need for a corresponding telephone service.
"Wet" versus "Dry"
Telephones originally needed a light electrical charge to detect when you picked up the phone and dialed a number. To provide this charge, batteries were placed on phone lines that generated dialtone. These are the "wet" loops. Dry loops are copper wire pairs that are not connected to these batteries, but may still be connected to switch panels at a central office.
How "Dry" Copper Sends Data
Telephone companies have long been using digital signals, even for phone calls. As a result, much of the infrastructure of public-switch telephone network is already set up to connect copper wires for virtually any communication service, including the Internet. In a dry loop, the telephone pairs are configured to connect directly to the appropriate networking equipment, bypassing the phone-switching equipment.
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Copmetition and Dry Loop Benefits
There are two main benefits to dry loop. For many customers, dry loop enables costs savings. Instead of paying the DSL fee and a telephone subscription, many can use their mobile phone as a home phone and order solely DSL service from their telephone company.
The second advantage is competition. Since FCC rules require local phone companies to play nice with communication providers, a start-up service provider only has to build the networking equipment, often called a central office, at your local publicly switched telephone network to begin offering you DSL. If you then order dry loop DSL service from the competitor, the local phone company is obligated to configure your wire pair, called provisioning, to point to the your DSL provider's network equipment.
The Fight Against Dry Loop
As might be expected, major phone companies have long fought the concept of dry loop. The dispute stems primarily from the telephone company's ability to receive federal funds for cost recovery on rural phone lines. Under current Federal Communications Commission rules, these funds are only available when a rural customer is a phone user -- broadband-only lines to not qualify for these funds. As the FCC has battled to marry old voice-only rules to new digital-based concepts, the ability to get dry DSL has ebbed and flowed. Today, it's often very difficult to get dry DSL, with carriers such as Verizon abandoning the service shortly after its offering.