News | January 20, 1999

xDSL a Possible Tool in Network Designers Kit

Source: BICSI: A Telecommunications Assoc.
BICSI: A Telecommunications Assoc.Is Digital Subscriber Line technology a possible alternative to structured wiring? The issue was explored this week at the BICSI Winter Conference. BICSI: A Telecommunications Assoc.By: John Spofford BICSI: A Telecommunications Assoc.Designers of communications networks should be aware of the potential applications of digital subscriber lines (xDSL)—a technology that allows the transmission of large amounts of data bandwidth over an ordinary telephone twisted pair. That was the conclusion reached by Joe Callahan, manager of data design at the engineering consulting firm Engineering Associates speaking at the <%=company%> Winter Conference this week in Orlando, FL. BICSI: A Telecommunications Assoc."Digital subscriber line technology does not threaten Category 5 in any way," he said. "But there are situations where knowing about xDSL and recommending it can make you a hero in the eyes of your customer or boss. [As a communication cabling designer] you have the opportunity to be first to see situations where xDSL might fit." BICSI: A Telecommunications Assoc.The Concept
Actually a number of similar technologies, hence the "x" in xDSL, digital subscriber lines were developed for the phone companies to carry high-speed data signals over voice-grade copper pairs. This is where the similarity ends. In most cases, the variations of xDSL do not interoperate. BICSI: A Telecommunications Assoc.The Many Flavors of xDSL

BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc. BICSI: A Telecommunications Assoc.
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"Standards" Based BICSI: A Telecommunications Assoc.

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Proprietary BICSI: A Telecommunications Assoc.

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HDSL BICSI: A Telecommunications Assoc.

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Paradyne MVL BICSI: A Telecommunications Assoc.

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SDLS BICSI: A Telecommunications Assoc.

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Nortel 1 Meg Modem BICSI: A Telecommunications Assoc.

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ADSL and RADSL BICSI: A Telecommunications Assoc.

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EtherLoop BICSI: A Telecommunications Assoc.

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IDSL BICSI: A Telecommunications Assoc.

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3 Com 10Base-S BICSI: A Telecommunications Assoc.

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G.Lite BICSI: A Telecommunications Assoc.

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Cisco EZ-DSL BICSI: A Telecommunications Assoc.

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VDSL BICSI: A Telecommunications Assoc.

BICSI: A Telecommunications Assoc.Currently xDSL technology is capable of carrying up to 8 Mbps on a 12,000-foot loop of 24-gauge wiring. Newer technologies such as VDSL are still in the lab but have the potential of carrying up to 52 Mbps on 1,000 ft of 24 gauge. BICSI: A Telecommunications Assoc."Existing voice cable plant is capable of carrying much more than voice bandwidth and xDSL takes advantage of that," Callahan said. "The technology is not really Ethernet, but it has an Ethernet interface to the user." Currently no xDSL product claims to handle the Token Ring protocol. BICSI: A Telecommunications Assoc.The technology works on the principle of different services for different customers. The variations vary drastically on the amount of bandwidth provided and the distance that the data can be carried. (See chart, below.) BICSI: A Telecommunications Assoc.Standards-based xDSL Flavors In Detail
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HDSL: High-bit rate DSL BICSI: A Telecommunications Assoc.

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BICSI: A Telecommunications Assoc.

4-wire
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1.5 Mbps symmetric to 12,000 ft BICSI: A Telecommunications Assoc.

BICSI: A Telecommunications Assoc.

SDSL: Single pair DSL BICSI: A Telecommunications Assoc.

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2-wire
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BICSI: A Telecommunications Assoc.

768 Kbps symmetric to 12,000 ft BICSI: A Telecommunications Assoc.

BICSI: A Telecommunications Assoc.

ADSL: Asymmetric DSL; RADSL: Rate-adaptive DSL

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BICSI: A Telecommunications Assoc.

2-wire
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BICSI: A Telecommunications Assoc.

Up to 8 Mbps downstream and up to 1 Mbps upstream at 12,000 ft, and lower speeds up to 18,000 ft BICSI: A Telecommunications Assoc.

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IDSL: ISDN DSL

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BICSI: A Telecommunications Assoc.

2-wire
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128 Kbps symmetric to 18,000 ft (uses ISDN line code) BICSI: A Telecommunications Assoc.

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G.Lite (Universal DSL)

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2-wire
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1.5 Mbps downstream and 256 Kbps upstream at 12,000 ft BICSI: A Telecommunications Assoc.

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VDSL: Very high-bit rate DSL

BICSI: A Telecommunications Assoc.
BICSI: A Telecommunications Assoc.

2-wire
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BICSI: A Telecommunications Assoc.

52 Mbps downstream and 2 Mbps upstream at 1,000 ft, 13 Mbps downstream and 2 Mbps upstream at 5,000 fee BICSI: A Telecommunications Assoc.

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BICSI: A Telecommunications Assoc.Where xDSL Fits in Structured Wiring
xDSL has the greatest potential use in non-telco settings such as hotels and multi-unit dwellings such as apartment building. The managers of these facilities often are interested in offering xDSL services such as high-speed Internet access or video-on-demand to tenants to make the properties more competitive. BICSI: A Telecommunications Assoc.xDSL is often the only way to retrofit high-speed data pathways into these buildings. BICSI: A Telecommunications Assoc."This is especially the case where adding new data cables would be a problem, but where telephone wire is already in place," Callahan said. BICSI: A Telecommunications Assoc.Obstacles to traditional structured wiring might include:
  • No place to put it: For example, an old building with wiring conduits that are cast in the floor and the conduits are simply out of space.
  • Too few drops: In some cases the potential number of users for a data service are too few to justify the cost of a cabling job.
  • Need it fast: The customer or the installer simply does not have the time to do a cabling job.
BICSI: A Telecommunications Assoc."You are not going to save any money doing this," Callahan warned. "The current cost of xDSL is quite high. If there are no obstacles to structured cabling, it is probably cheaper to go with cabling." BICSI: A Telecommunications Assoc.Uplink Costs
A characteristic of xDSL is that it only works on copper loops. If, for example, it is used to supply Internet access, xDSL will transmit data to and from the access multiplexer usually located in the wiring closet for a hotel or at the local central office in the case of telephone company-provided xDSL services. BICSI: A Telecommunications Assoc.The link between the digital subscriber line access multiplexer, or DSLAM, up to the Internet service provider is not xDSL, but a more traditional wide-area link. The high cost of this uplink, often a 45 Mbps T-3, can be a project killer, Callahan said. BICSI: A Telecommunications Assoc.About <%=company%>
Founded in 1974 and originally known as the Building Industry Consulting Services International, BISCI is an industry association that focuses on the technical aspects of combining communication cabling designs with the process of building design. Approximately 3,000 network designers, cable technicians, contractors, and installers attended the BISCI Winter Conference.