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| | Digital Subscriber Line (DSL) |
 | | VDSL is still in the definition stage; some preliminary products exist, but not enough is known yet about telephone line characteristics, radio frequency interface emissions and susceptibility, upstream multiplexing protocols, and information requirements to frame a set of definitive, standardizable properties. |
 | | This is unknown because real line characteristics at the frequencies required for VDSL are speculative, and items such as short bridged taps or unterminated extension lines in homes, which have no effect on telephony, ISDN, or ADSL, may have very detrimental affects on VDSL in certain configurations. |
 | | As line length shrinks, either from natural proximity to a central office or deployment of fiber-based access nodes, ADSL and VDSL simply offer more channels and capacity for services that require rates above T1/E1 (such as digital live television and virtual CD-ROM access). |
| www.cisco.com /univercd/cc/td/doc/cisintwk/ito_doc/adsl.htm (3937 words) |
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