There are two broad divisions of xDSL—asymmetric (ADSL) and symmetric (SDSL). Current and future types are summarized in Table 1-1.
|Asymmetric DSL||Symmetric DSL (Multiple Varieties of Symmetric DSL Are Marketed as “SDSL”)|
CAP— No standard
SDSL— No standard
G.DMT— (Worldwide) ITU G.992.1
HDSL— No standard
ADSL/ISDN (ADSL over ISDN)— No standard
HDSL2— (North America) ANSI T1.418
|DMT2-(North America) ANSI T1.413.2
“G.Lite” or “half-rate DMT”— (Worldwide) ITU G.992.2
IDSL— ISDN over DSL
G.dmt.bis (ADSL2)— (Worldwide) G.992.3
SHDSL— (Worldwide) ITU G.991.2
G.lite.bis (half-rate ADSL2)— (Worldwide) G.992.4
VDSL— No standard
The difference between asymmetric and symmetric service is simple: Either the ...