Security risks are incurred in this process.
DSL Types and Standards
The two basic types of DSL technologies are as follows:
?– Asymmetric DSL (ADSL): Provides higher download bandwidth than upload
bandwidth
?– Symmetric DSL (SDSL): Provides the same capacity of bandwidth in both directions
Figure 5-10 illustrates the difference between ADSL and SDSL.
Figure 5-10 Asymmetric Versus Symmetric DSL
Central Office
xDSL
Corporate
Network
Internet
Asymmetric DSL Symmetric DSL
Down Up Down Up
360 Chapter 5: WAN Connections
All forms of DSL services are categorized as asymmetric or symmetric, but several
varieties of each type exist. ADSL includes the following forms:
?– ADSL
?– Consumer DSL (CDSL), also called G.Lite or G.992.2
?– Very-high-data-rate DSL (VDSL)
SDSL includes the following forms:
?– SDSL
?– High-data-rate DSL (HDSL)
?– ISDN DSL (IDSL)
?– Symmetric high-bit-rate DSL (G.shdsl)
DSL service can be added incrementally in any area. A service provider can upgrade
bandwidth to coincide with a growth in numbers of subscribers. DSL is also backward
compatible with analog voice and makes good use of the existing local loop, which means
that it is easy to use DSL service simultaneously with normal phone service.
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