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ADSL Modems

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					ADSL Modems
Users who want to connect to ADSL broadband use the ADSL modem to do so.
ADSL modems are a very cost-effective solution for users and are popular
across the world, including the US. The ADSL modem enables the transfer
of Internet data directly to the computer. The data rates provided by
ADSL modems are consistent with North American and European digital
hierarchies. Users can purchase these modems from the market with various
speed ranges and capabilities. The minimum configuration enables data
rates of 1.5 or 2.0 Mbps downstream in a 16 kbps duplex channel. Other
configurations offer rates of 6.1 Mbps along with a 64 kbps duplex. One
can also opt for products with downstream rates of 8 Mbps and duplex
rates of up to 640 kbps.
There are three types of ADSL modems. They are the ethernet ADSL modem,
the PCI ADSL modem, and the USB ADSL modem. The ethernet ADSL modem can
be fed directly into a PC ethernet port or used to add a modem to certain
broadband routers. The PCI ADSL modem fits inside the computer. USB ADSL
modems are the most popular form of all ADSL modems, and they are
designed for connecting individual computers to ADSL lines.
Now, how does an ADSL modem function? The ADSL modem organizes the stream
of aggregate data in blocks. These data are created by multiplexing
downstream channels, the duplex channels, and the maintenance channels.
While transmitting the data, the ADSL modem attaches an error-correction
code to each block. ADSL modems are capable of accommodating ATM
transport with variable rates and compensation for ATM overhead, as well
as the IP protocols.
ADSL modems can create multiple channels to transfer data. For this, ADSL
modems divide the available bandwidth of a telephone line in one of two
ways - Frequency Division Multiplexing (FDM) and Echo Cancellation. The
FDM assigns one band for upstream data and assigns another band for the
downstream data. Further, the downstream path gets sub-divided into one
or more high-speed channels by time division multiplexing. Similarly, the
upstream path also gets multiplexed into corresponding low-speed
channels. Echo Cancellation enables the upstream band to overlap the
downstream band. These two bands get separated by means of local echo
cancellation. Both Frequency Division Multiplexing (FDM) and Echo
Cancellation techniques enable ADSL to split off a 4 kHz region for POTS
at the DC end of the band.
However, in spite of the tremendous capabilities of ADSL modems, it is
recommended that Internet users using modems should not be awed with the
technological capabilities of the modem, and install firewall software
for added security.
ADSL provides detailed information on ADSL, ADSL Modems, ADSL Web
Hosting, ADSL Routers and more. ADSL is affiliated with DSL Service.

				
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posted:10/18/2010
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