3.7. All-Digital Loop
The ITU Q4/15 update to the Recommendation G.992 includes an all-digital mode providing for the use of the 0 to 25 kHz band for upstream and/or downstream digital transmission. In essence, DMT tones fill this band in place of the traditional analog voice signal. The all-digital loop provides approximately 256 kb/s of additional capacity in each direction. The benefits of all-digital loop are most pronounced on long lines (over 14 kft) where there is little capacity at higher frequencies. The additional upstream capacity is particularly useful for voice-over DSL systems that require more nearly symmetric data rates.
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