Best of the ISP-Lists

DSL

Which xDSL and How Far?

ISP-DSL members discuss the physical limitations unique to the many flavors of copper-fed high-speed access.

[October 13, 2000]

On the ISP-DSL list in October, CS asked,

"Does anyone know of other ILECs that share Bell Atlantic's (now Verizon's) limit of 18,000 feet for DSL loops? We have loops over 30,000 feet that operate perfectly. Why do they have this limitation?"

A number of respondents suggested that it's an inherent restriction in the equipment:

[CW noted] "It's the limitation of the protocol. 30,000-foot loops are for IDSL. Verizon and, I am sure, Bell Atlantic, all use ADSL."

[CP added] "Isn't the limitation on ADSL due to the fact that any more amplification of the signal will cause an unworkable signal due to distortion? Last time I checked, the laws of physics were pretty much universal. The only way that I could see DSL going out to 28,000 feet (except IDSL) is if the telco has both crystal clear lines and thick copper. In our area, with constant 100% humidity, we are lucky to get ADSL to go farther than 8,000 feet."

But others told a different story:

[VB recounted] "BA/Verizon here will give me pretty much whatever loop length I want. Over 18,000 feet there's just a little waltzing on what they will allow to condition it."

[CH added] "The issue is not so much with the technology as it is with economics. Read the Verizon tariff: 'There are nonrecurring charges for removing bridge taps and load coils, unless the loop is under 18,000 ft.' The technology will allow IDSL to go out to seven miles. Depending on the provider, ADSL is around 12,000 feet and SDSL is around 16,000 feet, but there are new products coming out that can extend those limits."

Still others mentioned a new plan to resolve the issue:

[KP suggested] "You might want to do a search on Project Pronto, which is SBC/Ameritech's initiative to get everyone within 18,000 feet of a central office or remote switch."

[WD explained] "Project Pronto is a plan to put DSL hardware in line extender huts, called gateways, in every neighborhood. Doing this would take someone who is 30,000 feet from the CO but only 12,000 feet from the gateway and make them 12,000 feet from the nearest DSLAM. They're basically extending DSL service to the gateways and expanding their reachable base exponentially."

—End