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DSL technology provides high-speed,

and small businesses.

DSL utilizes the same cabling used fornormal tele hones but it can offer hi her

data rates through use of the digitalmo em ec no ogy.

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DSL modems comprise the heart of this

technolo and the lines themselves areactually just plain telephone lines.

'the same line for their digital and analog

tra ic play web + receive a call.

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Speed

DSL offers more than 100 times the

network erformance of a traditional

analog modem.

depends on the variety of xDSLep oye .

DSL is a distance-sensitive technology.

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DSL works on the unused (high).

DSL modems contain an internal

signal splitter that carries voicesignals on the usual lowfrequencies (from 0 up to 4kHz) and

data signals above that.

This splitter, consequently, allows

simultaneous access to the line bthe telephone and the computer.

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Access

DSL service remains "on" all of the time. People should be aware that long-lived

issues firewall.

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Availability

The technolo used to im lement DSL onlworks over a limited physical distance. At the

maximum DSL runs about 18 000 feet 3.5

miles or 5.5 kilometers) from a telephoneexchan e.

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Availability (cont.)

o e e g e or serv ce, ephone line involved must be

" ". the home or business must lie within

(18,000 feet).

sufficient electrical quality

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The actual network bandwidth a

customer will receive from DSL in

the home de ends on the s an of

their telephone wiring.

The longer the line, the less

bandwidth DSL can su ort.

Likewise, its thickness (wire gauge)

can affect performance.

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Cable length Bandwidth availability

18,000 1,544

16,000 2,048

12,000 6,312

9,000 8,448

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The xDSL "family tree" includes two main

branches Symmetric DSL services provide identical

.

Asymmetric DSLprovides relatively lower

.

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, . te an

VDSL (VADSL, BDSL)

IDSL

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Asymmetric Digital Subscriber Line

was designed to provide higher

downstream data rates at the expense of

upstream rates.

Mbps (roughly 6000 Kbps), but the

service customers actually receive

enerall erforms at 2 Mb s or lower for downloads and 512 Kbps for uploads.

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Example:

Man t ical uses of the Web -- such as filedownloads and general web browsing --

benefit from reater downstream bandwidth

but require relatively little in the oppositedirection.

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.

Universal ADSL (also known as G.Lite) is

a form of ADSL that im roves on one ofthe weaknesses of regular ADSL --

.

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.

Regular ADSL generally requires a

technician visit to the client site to installthe splitter device that divides the

.

G.Lite does not require that this splitter be

installed, but it does so at the expense o

lower data rates.

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.

G.Lite supports a maximum of 1,544 kbps

384 kb s u stream Whereas regular ("full-rate") ADSL can

, .

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Rate-Adaptive DSL (RADSL), is an

im lementation of ADSL that automaticallconfigures the modem at startup to adjust

phone line.

Like .Lite, RAD L supports a much

lower maximum date rate (1,088 kbps)than regular ADSL.

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High Bit / Data-Rate DSL (HDSL) offers

the same bandwidth both u stream anddownstream.

the basic data rate (1,544 kbps),

It can deliver a maximum rate of 2,048

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Symmetric DSL(SDSL) improves on the

older HDSL technolo b im lementinthe same basic data rate (1,544 kbps)

.

SDSL supports data rates up to 3,088

Kbps.

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Symmetric High-Bit-Rate DSL

a emp s o mprove on

both HDSL and SDSL by only

requiring a single line and byinte ratin low-level services of

interest to small businesses. ec no ogy can ranspor

data symmetrically at data rates

from 192 Kbps to 2,320 Kbps.

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Very High Data-Rate DSL (VDSL)

ori inall named VADSL 'A' forasymmetric) but later was extended to

varieties of DSL.

VD L relies on iber optic cabling.

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VDSL needs shorter cable lengths than

most other forms of DSL maximum 4,500feet as compared to 18,000 feet for regular

,

data rate (roughly 51,840 kbps).

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The bandwidth levels supported by VDSL

-

applications such as High-Definition

Television (HDTV) that requires, for

, , .

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The performance of VDSL depends

traversed by wiring: Shorter distances

mean faster networking.

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ISDN DSL (IDSL) implements a hybrid

DSL/ISDN solution. IDSL offers only limited data rates (128

,bonded).

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Speed

Cable modem generally wins the

s eed battle over DSL.

Cable technology can, in theory,

approximately 30 Mbps (using a 100ps

Most forms of DSL cannot reach 10Mbps.

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Speed (cont.)

cable modem technolo delivers sharedbandwidth within the local neighborhood

.

Security (cont.)

Many DSL and cable modem customers

choose to purchase routers to protect theirinternal systems.

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Security

At Northwestern University, Kellogg

Information S stems

If ease of installation is important to

,

DSL. The slightly more secureenv ronmen o ere y s no

enough to justify the added cost and

installation hassle."