What does it all mean
DSL: (digital subscriber line) a technology that exploits
unused frequencies on copper telephone lines to transmit traffic typically at
multi-megabit speeds. DSL can allow voice and high-speed data to be sent
simultaneously over the same line. Because the service is 'always available,'
end-users don't need to dial in or wait for call set-up. With DSL you are wired
- Asymmetric flavors
Asymmetrical variations include: ADSL, G.lite ADSL (or simply G.lite),
RADSL and VDSL. The standard forms of ADSL (ITU G.992.1, G.992.2, and ANSI
T1.413-Issue 2) are all built upon the same technical foundation, Discrete
Multi Tone (DMT). The suite of ADSL standards facilitates interoperability
between all standard forms of ADSL.
- ADSL: (Full Rate asymmetrical DSL) ADSL offers differing
upload and download speeds and can be configured to deliver up to six megabits
of data per second (6000K) from the network to the customer that is up to
120 times faster than dialup service and 100 times faster than ISDN. ADSL
enables voice and high-speed data to be sent simultaneously over the existing
telephone line. This type of DSL is the most predominant in commercial use for
business and residential customers around the world. Good for general Internet
access and for applications where downstream speed is most important, such as
video-on-demand. ITU-T Recommendation G.992.1 and ANSI Standard T1.413-1998
specify full rate ADSL.
- G.lite ADSL (or simply G.lite): The G.lite standard was
specifically developed to meet the plug-and-play requirements of the consumer
market segment. G.lite is a medium bandwidth version of ADSL that allows
Internet access at up to 30 times the speed of the fastest 56K analog modems ~
up to 1.5 megabits downstream and up to 500 kilobits upstream. G.lite is an
International Telecommunications Union (ITU) standard, globally standardized
interoperable ADSL system per ITU G.992.2.
- RADSL: (rate adaptive DSL) A non-standard version of ADSL. Note
that standard ADSL also permits the ADSL modem to adapt speeds of data
- VDSL (very high bit rate DSL) Up to 26 Mb/s, over distances
up to 50 Meters on short loops such as from fiber to the curb. In most cases,
VDSL lines will be served from neighborhood cabinets that link to a Central
Office via optical fiber. It is particularly useful for 'campus' environments
- universities and business parks, for example. VDSL is currently being
introduced in market trials to deliver video services over existing phone
lines. VDSL can also be configured in symmetric mode.
Symmetrical variations include: SDSL, SHDSL, HDSL, HDSL-2 and IDSL The
equal speeds make Symmetrical DSLs useful for LAN (local area network) access,
video-conferencing, and for locations hosting their own Web sites.
- SDSL: (symmetric DSL) SDSL is a vendor-proprietary version of
symmetric DSL that may include bit-rates to and from the customer ranging of
128 kbps to 2.32 Mbps. SDSL is an umbrella term for a number of
supplier-specific implementations over a single copper pair providing variable
rates of symmetric service. SDSL uses 2B1Q HDSL run on a single pair with an
Ethernet interface to the customer. The industry is expected to quickly move
towards the higher performing and standardized G.shdsl technology developed by
the ITU with support from T1E1.4 (USA) and ETSI (European Telecommunications
- SHDSL is state-of-the-art, industry standard symmetric DSL SHDSL
equipment conforms to the ITU Recommendation G.991.2, also known as G.shdsl,
approved by the ITU-T February 2001. SHDSL achieves 20% better loop-reach than
older versions of symmetric DSL, it causes much less crosstalk into other
transmission systems in the same cable, and multi-vendor interoperability is
facilitated by the standardization of this technology. SHDSL systems may
operate at many bit-rates, from 192 kbps to 2.3 Mbps, thereby maximizing the
bit-rate for each customer. G.shdsl specifies operation via one pair of wires,
or for operation on longer loops, two pairs of wire may be used. For example,
with two pairs of wire, 1.2 Mbps can be sent over 20,000 feet of 26 AWG wire.
SHDSL is best suited to data-only applications that need high upstream
bit-rates. Though SHDSL does not carry voice like ADSL, new voice-over-DSL
techniques may be used to convey digitized voice and data via SHDSL. SHDSL is
being deployed primarily for business customers.
- HDSL: (high data rate DSL) This variety created in the late
1980s delivers symmetric service at speeds up to 2.3 Mbps in both directions.
Available at 1.5 or 2.3 Mbps, this symmetric fixed rate application does not
provide standard telephone service over the same line and is already
standardized through ETSI and ITU (International Telecommunications Union).
Seen as an economical replacement for T1 or E1, it uses one, two or three
twisted copper pairs.
- HDSL2: (2nd generation HDSL) This variant delivers 1.5 Mbps
service each way, supporting voice, data, and video using either ATM
(asynchronous transfer mode), private-line service or frame relay over a
single copper pair. This ANSI (American National Standards Institute) standard
for this symmetric service gives a fixed 1.5 Mbps rate both up and downstream.
HDSL2 does not provide standard voice telephone service on the same wire pair.
HSDL2 differs from HDSL in that HDSL2 uses one pair of wires to convey 1.5
Mbps whereas ANSI HDSL uses two wire pairs.
- IDSL: (integrated services digital network DSL) This is a
form of DSL that supports symmetric data rates of up to 144 Kbps using
existing phone lines. It is unique in that it has the ability to deliver
services through a DLC (Digital Loop Carrier: a remote device often placed in
newer neighborhoods to simplify the distribution of cable and wiring from the
phone company). While DLCs provide a means of simplifying the delivery of
traditional voice services to newer neighborhoods, they also provide a unique
challenge in delivering DSL into those same neighborhoods. IDSL addresses this
market along with ADSL and G.lite as they are implemented directly into those
DLCs. IDSL differs from its relative ISDN (integrated services digital
network) in that it is an "always-available" service, but capable of using the
same terminal adapter, or modem, used for ISDN.