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ADSL
Asymmetric Digital Subscriber Line – or, as
it is known in the United States, Asymmetric Digital Subscriber Loop -
is a digital transmission technique for enhancing the
information-carrying capacity of traditional copper pair cables in the
local access network. Since the bandwidth of the return channel is less
than that of the outgoing channel, the technique is described as
asymmetric. It was originally conceived as suitable for video on demand
services by delivering video signals to the customer's premises with a
low-capacity return channel for customer selection or ordering purposes.
However, ADSL has become the principal means of delivering broadband
telecommunications services to domestic premises - originally at 512
kilobits a second, but now (especially through local loop unbundling) up
to 8 Megabits a second.
ADSL uses two separate frequency bands. With standard ADSL, the
band from 25.875 kHz to 138 kHz is used for upstream communication,
while 138 kHz – 1104 kHz is used for downstream communication.
ADSL2
ADSL services typically operate at a maximum speed of 1.5
megabits per second (Mbps), supporting e-mail, Web access, Voice over
Internet Protocol (VoIP) and some multimedia applications. ADSL2
is an enhanced version delivering speeds of up to 12 Mbps.
ADSL2+
ADSL2+ reached consent at the International Telecommunications
Union (ITU) in January 2003, joining the ADSL and ADSL2 standards
family. While the first two members of the ADSL2 standards family
specify a downstream frequency band up to 1.1 MHz and 552 kHz
respectively, ADSL2+ specifies a downstream frequency up to 2.2 MHz. The
result is a significant increase in data rates on shorter phone lines,
doubling the downstream bandwidth and increasing the downstream data
rate to as much as 24 Mbps. Although the technological standard behind
ADSL2+ was agreed some time ago, its introduction in the UK has been
hampered by the fact that it interferes with another technology called
Very high speed Digital Subscriber Line (VDSL). Other countries that
have implemented ADSL2+ have been forced to ban VDSL. In Britain,
however, a technological solution has now been found to allow both
technologies to be used.
SDSL
SDSL is the next serious step forward from an ADSL or leased line
connection. Here are some of the reasons why so many businesses are
upgrading to SDSL:
• Up to 50% cheaper than leased line.
• Connect business sites together, cost effectively and at high speeds.
• Provide teleworkers a fast and efficient connection to you servers.
• Upload 8 x faster than traditional ADSL broadband and upload as fast
as it downloads.
• Allow large and fast file transfers, video streaming and video
conferencing.
• 25xfaster than dial up and 16 x faster than ISDN.
• Always on connection, allowing you to run mail and web servers, Voice
over IP, VPNs (virtual private network) and other mission critical
applications to make your business more productive.
• Send & receive e-mails with larger attachments.
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