Modem DSL DSL Digital Subscriber Line

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					DSL. DSL (Digital Subscriber Line) technology uses the same twisted copper telephone
lines as standard dial-up and ISDN, but with drastically improved speed. DSL can be up
to 140-plus times faster than 56Kbps modems, and up to more than 60 times faster than
ISDN. It's also popular because it's relatively inexpensive compared to other broadband
connection options.

The increased speed found with this type of Internet connection is achieved by using
sophisticated modulation technology in a direct connection between DSL-connected
computers and the telephone company. In fact, your computers' physical distance from
the phone company determines, in large part, the speed of your DSL connection. That's
why it's a good idea to subscribe to DSL only if the phone company providing it is
located close by, at least within three or four miles.

There are different types of DSL available. The most common are ADSL (Asymmetrical
Digital Subscriber Line) and SDSL (Symmetrical Digital Subscriber Line).

With ADSL, data downloads take place up to 8 megabytes per second (Mbps), and
uploads are up to 1Mbps. This type of service is ideal for businesses needing access to
the World Wide Web and the ability to send and receive large multimedia files.

SDSL offers the same download and upload speeds: up to 1.544 megabits (not
megabytes) per second. This symmetrical speed makes it ideal for e-mail and web servers
on small networks as well as interoffice communications. It is also often more expensive
than ADSL and doesn't support standard phone services.

Broadband connections such as DSL-in a huge advantage over standard dial-up and
ISDN-are an "always-on" connection, meaning computers with DSL connection have
continuous connections to the Internet. This is an important consideration if you have
many workers who need frequent access to the Internet and the ability to send and receive
large data files.

Cable. A cable Internet connection, unlike the previous types of connections we've
discussed, doesn't use phone lines at all. Instead, this technology takes advantage of
existing television cable lines and "cable modems" to transfer data at very fast rates:
42Mbps for downloads and 10Mbps for uploads.

This type of connection is heavily marketed by cable companies to residential areas,
given that most homes are already wired with television cables. This makes it a popular
choice for home offices, although the subscription rates are higher than dial-up
connections and DSL. Still, the price is generally reasonable for small businesses and the
high-speed, always-on connection makes for a highly reliable and very fast Internet

Because of the continuous connection that flows through phone cables, cable
connections, like DSL connections, are not highly secure from unauthorized entry by
hackers. It's highly recommended that computers with these types of connection are
protected by a firewall (a set of related hardware and software used to protect a network).

T1 and T3. These high-speed Internet voice and data networks are very expensive and
recommended only for larger companies using a computer network.

A T1 line is a high-speed, always-on, highly reliable connection established usually with
fiber-optic lines that can carry 24 digital voice channels or data at a rate of up to a
phenomenally fast 1.544 megabits per second. T1 connections are often used for both a
company's phone system as well as a high-speed, always-on Internet connection. A T1
connection is usually shared by many workers at a company simultaneously needing
continuous high-speed Internet access.

A T3 line is used most often for huge networks, like those that comprise the Internet or
for hosting heavily visited websites. Digital data is transferred at 44.746 megabits per
second, a huge broadband connection needed by only the largest networks and website

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