D
|
igital
subscriber line (DSL; originally digital subscriber loop)
is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely
understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology,
for Internet access.
DSL service can be delivered simultaneously with wired telephone service on the same telephone line since DSL uses
higher frequency bands for
data. On the customer premises, a DSL filter on each non-DSL outlet blocks any high-frequency
interference to enable simultaneous use of the voice and DSL services.
The bit rate of consumer DSL services typically ranges from
256 kbit/s to over 100 Mbit/s in the direction to the customer (downstream), depending on DSL technology, line conditions, and
service-level implementation. Bit rates of 1 Gbit/s have been reached in trials,[1] but most homes are likely to be limited to 500-800
Mbit/s. In ADSL, the data throughput in the upstream direction
(the direction to the service provider) is lower, hence the designation
of asymmetricservice. In symmetric digital subscriber line (SDSL) services, the downstream and upstream data
rates are equal. Researchers at Bell Labs have reached speeds of 10 Gbit/s, while delivering
1 Gbit/s symmetrical broadband access services using traditional copper
telephone lines. These higher speeds are lab results, however.[2][3] A 2012 survey found that "DSL continues to be
the dominant technology for broadband access" with 365.1 million
subscribers worldwide.
·
You can leave your Internet connection open and still use the
phone line for voice calls.
·
The speed is much higher than a regular modem
·
DSL doesn't necessarily require new wiring; it can use the phone
line you already have.
·
The company that offers DSL will usually provide the modem as
part of the installation.
But there are disadvantages:
·
A DSL connection works better when you are closer to the
provider's central office. The farther away you get from the central office,
the weaker the signal becomes.
·
The
connection is faster for receiving data than it is for sending data over the
Internet.
·
The service is not available everywhere.
In
this article, we explain how a DSL connection manages to squeeze more
information through a standard phone line -- and lets you make regular
telephone calls even when you're online.
Telephone Lines
If you have read How
Telephones Work, then you know that a standard telephone
installation in the United States consists of a pair of copper wires that the
phone company installs in your home. The copper wires have lots of room for
carrying more than your phone conversations -- they are capable of handling a
much greater bandwidth, or range of frequencies, than that demanded
for voice. DSL exploits this "extra capacity" to carry information on
the wire without disturbing the line's ability to carry conversations. The
entire plan is based on matching particular frequencies to specific tasks.
To understand DSL, you first need to know a couple of
things about a normal telephone line -- the kind that telephone professionals
call POTS, for Plain Old Telephone Service. One of the ways that
POTS makes the most of the telephone company's wires and equipment is by
limiting the frequencies that the switches, telephones and other equipment will
carry. Human voices, speaking in normal conversational tones, can be carried in
a frequency range of 0 to 3,400 Hertz (cycles per second -- see How
Telephones Work for a great demonstration of this).
This range of frequencies is tiny. For example, compare this to the range of
most stereo speakers, which cover from roughly 20 Hertz to 20,000 Hertz. And
the wires themselves have the potential to handle frequencies up to several
million Hertz in most cases.
The use of such a small portion of the wire's total
bandwidth is historical -- remember that the telephone system has been in
place, using a pair of copper wires to each home, for about a century. By
limiting the frequencies carried over the lines, the telephone system can pack
lots of wires into a very small space without worrying about interference
between lines. Modern equipment that sends digital rather than analog data can
safely use much more of the telephone line's capacity. DSL does just that.
Digital Subscriber Line (DSL) is
a high-speed Internet service for homes and businesses that competes with
cable and other forms of broadband
Internet. DSL provides high-speed networking over ordinary phone
lines using broadband
modem technology. The technology behind DSL enables
Internet and telephone service to work over the same phone line without
requiring customers to disconnect either their voice or Internet connections.
DSL Speed
Basic DSL supports maximum download data
rates ranging between 1.544 Mbps and 8.448 Mbps.
Actual speeds vary in practice depending on the quality of the copper phone
line installation involved. The length of the phone line needed to reach the
service provider's premise equipment (sometimes called the "central
office") also can limit the maximum speed a DSL installation supports.
Symmetric vs. Asymmetric DSL
Most types of
DSL service are asymmetric—also known as ADSL.
ADSL offers higher download speeds than upload speeds, a tradeoff that most
residential providers make to better match up with the needs of typical
households who generally do much more downloading. Symmetric DSL maintains
equal data rates for both uploads and downloads.
Residential DSL Service
Well-known DSL providers in the United States
include AT&T (Uverse), Verizon, and Frontier Communications.
Many smaller regional providers also
offer DSL. Customers subscribe to a DSL service plan and pay a monthly or
yearly subscription and must also agree to the provider's terms of
service. Most providers supply compatible DSL modem hardware to their
customers if needed, although the hardware is generally available through
retailers.
Business DSL Service
Besides
its popularity in homes, many businesses also rely on DSL for their Internet
service. Business DSL differs from residential DSL in several key respects:
- Symmetric
DSL is typically used as businesses tend to generate much higher volumes
of outgoing traffic than a typical home
- Providers
often sell higher tiers of service to their customers including higher
data rate plans, premier customer support options or bundling of other
products
For more, see: Introduction
to DSL for Business Internet Service
Problems with DSL
DSL Internet service only works over a
limited physical distance and remains unavailable in many areas where the local
telephone infrastructure does not support DSL technology.
Although DSL has been a mainstream type of
Internet service for many years, the experience of individual customers can
vary greatly depending on their location, their provider, the quality of
telephone wiring in their residence and some other factors.
As with other forms of Internet service, the
cost of DSL can vary dramatically from region to region. An area with few
Internet connectivity options and few providers may be more costly simply due
to the lack of business competition.
DSL does not perform nearly as fast as fiber
Internet connections. Even some high-speed wireless Internet
options can offer competitive speeds.
Because DSL lines use the same copper wire as
wired telephone service, all wired phones in the home or business must use
special filters that plug in between the phone and the wall jack. If these
filters aren't used, the DSL connection may be adversely affected.
"Digital Subscriber Line." DSL is a
communications medium used to transfer digitalsignals over standard
telephone lines. Along with cable Internet, DSL is one of the most popular ways ISPs provide broadbandInternet access.
When you make a telephone call using
a landline, the voice signal is transmitted using low frequencies from 0 Hz to 4 kHz. This range, called
the "voiceband," only uses a small part of the frequency range
supported by copper phone lines. Therefore, DSL makes use of the higher
frequencies to transmit digital signals, in the range of 25 kHz to 1.5 MHz. While these
frequencies are higher than the highest audible frequency (20 kHz), then can
still cause interference during phone conversations. Therefore, DSL filters or
splitters are used to make sure the high frequencies do not interfere with
phone calls.
Symmetric DSL (SDSL) splits the upstream
and downstream frequencies evenly, providing equal speeds for both sending and
receiving data. However, since most users download more data than
they upload, ISPs typically offer asymmetric
DSL (ADSL) service. ADSL provides a wider
frequency range for downstream transfers, which offers several times faster
downstream speeds. For example, an SDSL connection may provide 2 Mbps upstream
and downstream, while an ASDL connection may offer 20 Mbps downstream and 1.5
Mbps upstream.
In order to
access the Internet using DSL, you must connect to a DSL Internet service
provider (ISP). The ISP will provide you with a DSL modem, which you can
connect to either a router or a computer.
Some DSL modems now have built-in wireless routers, which
allows you to connect to your DSL modem via Wi-Fi. A DSL kit may also
include a splitter and filters that you can connect to landline phones.
NOTE: Since DSL signals have a limited
range, you must live within a specific distance of an ISP in order to be
eligible for DSL Internet service. While most urban locations now have access
to DSL, it is not available in many rural areas.
How does it work?
DSL
brings a connection into your home through telephone lines and allows the
household to use the Internet and make telephone calls at the same time. It
works because the DSL system separates the telephone signals into three bands
of frequencies. The lowest band allows for telephone calls, while the other two
bands take care of uploading and downloading online activity.
Cable companies provide a cable
modem for their Internet customers. DSL companies provide a similar piece of
hardware called a DSL transceiver.
Who provides it?
Since
DSL uses telephone wires, it makes sense that the biggest providers are
telephone companies. AT&T is the largest telecommunications company in the
world and is also the largest provider of DSL service. Verizon and Century Link
are also major providers of DSL.
How popular or common is it in 2016?
DSL
isn't as popular today as it was 20 years ago because the companies that
provide it are mostly phasing it out and switching to the next generation of
Internet technology: fiber optics. Also, cable companies, which are widely
available, can typically provide a much faster connection to the Internet than
DSL.
How fast is it?
The
better question might be, "How slow is it?" Much slower than a cable
connection (Comcast, Cox Communications, Time-Warner, etc.) and incredibly
slower compared to fiber optic connections, such as FIOS (which is not
available everywhere).
"Fast
speed" according to some DSL providers is only 1.5 Mbps (megabits per
second). "Lightning" speed, their top, is 15 Mbps. The typical speed
for a DSL connection is 6 Mbps, compared to the 100 Mbps top speeds offered by
many cable companies. The midrange cable Internet plan likely promises 25-50
Mbps.
Has it improved or does it get better?
Yes.
For starters, today's DSL is likely ADSL, which was an improvement to the
initial technology. But more than that, there is now ADSL+2, described as
"an extension to ADSL broadband technology" that boosts download
speeds significantly. ADSL2+ has taken the capability of DSL from 7.1 Mbps to
up to as much as 15 Mbps downstream, or downloading speed, which is what matters
to most people.
But not so fast: Most likely, you
still would have to live in a major city and highly populated area to
find ADSL2+ available, and you'd have to live close
to the telephone company's "central office" to enjoy the service the
way you'd want to. So check with your local telephone company to see if it's
even available.
Is it in decline?
Yes.
If people have a choice, have done their homework and want a faster connection,
they most likely won't settle for DSL in any form. It's all about speed, and
old-fashioned DSL is on its way out.
The
fact is, new reports say that DSL providers would prefer to phase out DSL in
favor of the latest technology: fiber optics. This doesn't sit well with the
Federal Communications Commission, which doesn't like the idea of large
companies abandoning customers or forcing them to switch to better—and
higher-priced—services, even if the product is much better.
What are the advantages of DSL?
In
most scenarios, you'd likely want DSL only if your other alternative were
old-fashioned, low-cost dial-up service, which surprisingly is still available
in many areas. Compared to dial-up, DSL offers you advantages:
1.
You're able to use the Internet and make phone calls
simultaneously.
2.
It's faster than dial-up.
3.
You have a choice of price plans, based on the speed you want or
are willing to get.
That
seems like a good start, but there are some disadvantages nonetheless:
1.
Sending data won't work as well or as fast as receiving data.
2.
The further you are from the telephone company's central location,
the slower your service might be (we're not talking hundreds of miles
either—more like just under four miles).
3.
Sorry. You just might be too far away to even be offered DSL.
If you had a choice.
It's
hard to imagine that most individuals and families would settle for slow
Internet service if there were another Internet connection option available.
Then again, most people simply stick to what they're used to.
1.
If you currently have DSL and you find it frustrating, it might
be time to see if high-speed Internet from a cable company (Cox, Time-Warner,
etc.) is available.
2.
If you are with a cable company now and you don't like their
prices, you might want to downsize to DSL to save some money...but then you'd
have to live with DSL's limitations.
How it works
DSL connections are run through the phone lines in your home. This
technology channels your Internet connection and phone service through the same
wires. It uses a piece of equipment called a “splitter” to allow users to
access both phone and Internet at the same time.
DSL once required customers to get phone service if they wanted
Internet service as well. However, this is no longer a requirement. It is
possible to subscribe solely to DSL Internet now. This is called Naked DSL.
DSL offers Internet speeds in a range of 1.5 to 40 Mbps on average. Your speed depends on the plan you sign up for, the devices you use, where you are located and the activities you do on the Internet.
Installation
Most DSL providers offer either a self-install option or professional
install. The installation method you qualify for depends on your area, your
plan and your provider. Because DSL works through phone lines, your home must
have phone lines in order to set up Internet connection or you may need to get
them installed.
For DSL, in most cases, lines are already set up so installation
is easy. For self-installments, your provider will send you all the equipment
and instructions you need in the mail. Then they will send someone out to
activate your address as an active DSL customer. This lets their system know to
provide you with their Internet connection.
Connecting devices
You will need a modem and a router or a piece of equipment that
works as both. The modem converts the Internet connection into usable Internet
for your compatible devices. The router then emits the signal, allowing your
devices to connect wirelessly.
You can set up Internet
connection to your device either wirelessly or using an Ethernet cord. Wireless
is good for mobile devices and connecting anywhere in the house. The Ethernet
cable is good for consistent, smooth DSL connection that is used by only one
device.
Types of DSL
ü
VDSL
ü
CDSL
ü
HDSL
ü
IDSL
ü
RADSL
ü
SDSL
ü
UDSL
ü x2/DSL
ADSL
T
|
he
variation called ADSL (Asymmetric Digital Subscriber Line) is the form of DSL
that will become most familiar to home and small business users. ADSL is called
"asymmetric" because most of its two-way or duplex bandwidth is devoted to the
downstream direction, sending data to the user. Only a small portion of
bandwidth is available for upstream or user-interaction messages. However, most
Internet and especially graphics- or multi-media intensive Web data need lots
of downstream bandwidth, but user requests and responses are small and require
little upstream bandwidth. Using ADSL, up to 6.1 megabits per second of data
can be sent downstream and up to 640 Kbps upstream. The high downstream
bandwidth means that your telephone line will be able to bring motion video,
audio, and 3-D images to your computer or hooked-in TV set. In addition, a
small portion of the downstream bandwidth can be devoted to voice rather data,
and you can hold phone conversations without requiring a separate line.
Unlike
a similar service over your cable TV line, using ADSL, you won't be competing
for bandwidth with neighbors in your area. In many cases, your existing telephone
lines will work with ADSL. In some areas, they may need upgrading.
ADSL
was specifically designed to exploit the one-way nature of most multimedia
communication in which large amounts of information flow toward the user and
only a small amount of interactive control information is returned. Several
experiments with ADSL to real users began in 1996. In 1998, wide-scale
installations began in several parts of the U.S. In 2000 and beyond, ADSL and
other forms of DSL are expected to become generally available in urban areas.
With ADSL (and other forms of DSL), telephone companies are competing with
cable companies and their cable modem services.
For ADSL to work, only a
microfilter and an ADSL modem need to be installed and so installation
typically only takes a few hours, including the settings for the connection.
With real-world speeds of about 2Mbps, it is well suited to home use.`
A
special filter called a microfilter is needed in order for the regular voice
service and ADSL to be used at the same time. It is installed in the telephone
line just before the modem and the telephone. Both modem and telephone connects
to the microfilter.
Technically,
ADSL can reach speeds of up to 6Mbps, but only receives 2Mbps downstream
(download) and 512Kbps upstream (upload) speeds.
ADSL
can only be distributed within short distances from the central office, usually
less than 2.5 miles. It may exceed 5 miles if the gauge of the existing wires
allow for further distribution.
You need to be in an
Optus DSL or Optus DSL Direct coverage area to get ADSL. Visit our broadband service checker to
see which broadband technology is available where you are.
HEADS UP: Naked broadband and entertainment bundles are not
available on Optus DSL.
If you already know you can get ADSL, head on over to take a look at our plans
VDSL
VDSL (Very high data rate DSL) is a developing technology that
promises much higher data rates over relatively short distances (between 51 and
55 Mbps over lines up to 1,000 feet or 300 meters in length). It's envisioned
that VDSL may emerge somewhat after ADSL is widely deployed and co-exist with
it. The transmission technology (CAP, DMT, or other) and its effectiveness in
some environments is not yet determined. A number of standards organizations
are working on it.
How
VDSL Works
The use of fast Internet
connections has grown rapidly over the last few years. As more people buy home
computers and create home
networks, the demand for broadband (high-speed)
connections steadily increases. Two technologies, cable
modems and Asymmetric Digital Subscriber
Line(ADSL), currently dominate the industry.
While both of these technologies provide Internet
connections that are many times faster than a 56K modem, they still are not
fast enough to support the integration of home services such as digital television and video-on-demand.
However, another DSL
technology known as very high bit-rate DSL(VDSL) is seen by many as
the next step in providing a complete home-communications/entertainment
package. There are already some companies, such as U.S. West (part of Qwest
now), that offer VDSL service in selected areas. VDSL provides an incredible
amount of bandwidth, with speeds up to about 52 megabits per second (Mbps).
Compare that with a maximum speed of 8 to 10 Mbps for ADSL or cable modem and
it's clear that the move from current broadband technology to VDSL could be as
significant as the migration from a 56K modem to broadband. As VDSL becomes
more common, you can expect that integrated packages will be cheaper than the
total amount for current separate services.
In this article, you'll learn about VDSL technology, why
it's important and how it compares to other DSL technologies. But first, let's
take a look at the basics of DSL.
A
standard telephone installation in the United States consists of a
pair of copper wires that the phone company installs in your home. A pair of
copper wires has plenty of bandwidth for carrying data in addition to voice
conversations. Voice signals use only a fraction of the available capacity on
the wires. DSL exploits this remaining capacity to carry information on the
wire without disturbing the line's ability to carry conversations.
Standard
phone service limits the frequencies that the switches, telephones and other
equipment can carry. Human voices, speaking in normal conversational tones, can
be carried in a frequency range of 400 to 3,400 Hertz (cycles per second). In
most cases, the wires themselves have the potential to handle frequencies of up
to several-million Hertz. Modern equipment that sends digital (rather than
analog) data can safely use much more of the telephone line's capacity, and DSL
does just that.
VDSL could
change the face of E-commerce by allowing all types of media to run smoothly
and beautifully through your computer. Click here to learn more about E-commerce
VDSL
broadband is available to approximately 60% of existing Broadband users around
NZ. The defining factor is whether your local telephone cabinet has been
upgraded to enable VDSL. Even if your local cabinet is VDSL capable, distance
is still a factor. If your home is within 750 to 900 meters of the VDSL enabled
local roadside cabinet then VDSL should work for you.
How fast is VDSL?
VDSL is full line speed both ways, and is
around 5x faster than ADSL for downloads, and approximately 10 x faster for
uploads than ADSL. VDSL can reach speeds of more than 50 Mbps downstream,
and 10 Mbps upstream. Currently VDSL users are experiencing speeds that
are significantly faster than the entry level plan on the Ultra Fast Broadband
(Fibre) network.
Like ADSL, it is important to be aware
that the upstream and downstream line speed may be limited by external factors
including line quality, distance from the exchange and hardware quality.
Why
VDSL?
- Faster connection
speed and greater capacity than ADSL broadband
- Now Publish files
faster than before
- Best option For
high speed with suitable prices
- Experience best
quality video conference without frozen image
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