ADSL, HDSL, IDSL, SDSL .........
Different type of DSL modem
: ADSL, HDSL, IDSL, SDSL ..............
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Type of DSL And Modem
DSL uses the existing phone line and in most cases does not require
an additional phone line. This gives "always-on" Internet access and does
not tie up the phone line. There won't be any more busy tone from phone
line, no more dropped connections, no more waiting for someone in the
household to get off the phone. DSL offers users a choice of speeds ranging
from 144 Kbps to 1.5Mbps. The DSL speed is 2.5x to 25x times faster than a
standard 56Kbps dial-up modem. This digital service can be used to deliver
bandwidth-intensive applications like streaming audio/video, online games,
application programs, telephone calling, video conferencing and others
high-bandwidth services within smaller time frame.
DSL Modem
ADSL (Asymmetric
Digital Subscriber Line) - ADSL has data rate of .544 to
6.1 Mbps downstream; 16 to 640 Kbps upstream. And the distance limit for
this type of DSL is 1.544 Mbps at 18,000 feet; 2.048 Mbps at 16,000 feet;
6.312 Mpbs at 12,000 feet; 8.448 Mbps at 9,000 feet. ADSL is normally
used for Internet and Web access, motion video, video on demand, remote
LAN access
HDSL (High
bit-rate Digital Subscriber Line)
- HDSL is the earliest version of DSL to be used for wideband digital
transmission within a corporate site and between the telephone company
and a customer. The main characteristic of HDSL is that it is
symmetrical: an equal amount of bandwidth is available in both
directions. For this reason, the maximum data rate is lower than for
ADSL. HDSL can carry as much on a single wire of twisted-pair as can be
carried on a T1 line in North America or an E1 line in Europe (2,320
Kbps).
IDSL (ISDN
Digital Subscriber Line)
- IDSL is somewhat of a misnomer DSL modem since it's really close to ISDN data
rates and service at 144 Kbps than to the much higher rates of ADSL. IDSL is usually not sold by ADSL providers, is symmetric ("duplex"),
with the biggest advantage being the distance it can travel (5-6 miles).
Similar to ISDN (128 Kbps) but uses the control channel to increase data
rates to 144 Kpbs.
RADSL (Rate-Adaptive
DSL)
- is an ADSL technology from Westell in which software is able to
determine the rate at which signals can be transmitted on a given
customer phone line and adjust the delivery rate accordingly. Westell's
FlexCap2 system uses RADSL to deliver from 640 Kbps to 2.2 Mbps
downstream and from 272 Kbps to 1.088 Mbps upstream over an existing
line.
SDSL (Symmetric
DSL)
- is apparently the same thing as HDSL with
a single line, carrying 1.544 Mbps (U.S. and Canada) or 2.048 Mbps
(Europe) each direction on a duplex line. It is considered to be the
"business grade" DSL because of its symmetric speeds. SDSL is slower
than ADSL but usually marketed with Service Level Agreement (SLA) such
as the network will be guaranteed up for 99.5%, and there will be a
24-hour response time for every problem.
UDSL (Unidirectional DSL)
- is a proposal from a European company. It's a unidirectional version
of HDSL.
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 are not yet
determined. A number of standards organizations are working on it.
xDSL
- Refers collectively to all types of Digital Subscriber Lines, the two
main categories being ADSL and SDSL.
x2/DSL
- is a planned modem from 3Com and US Robotics that
supports 56 Kbps modem communication but is upgrade-able through new
software installation to ADSL when it becomes available in the user's
area. 3Com calls it "the last modem you will ever need."
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