SDSL (Symmetric digital subscriber line) allows broadband data services
to be carried on conventional copper pair telephone cables. SDSL is a single-pair alternative to HDSL, providing data rates
(or speed) up to 1 Mbps duplex (i.e. for both
upstream and downstream traffic).
The term "symmetric" in ADSL refers to
the difference in uplink and downlink capacities; the same capacity
is provided for the downlink as for the uplink. This
means that the same number of tones are allocated for
downlink data as for uplink data.
SDSL is based on
an adaptive, multi-tone modulation system. Each tone carries a part
of either the uplink or the downlink bitstream. Because the
bitstreams are split across a number of tones, the symbol
rate on the link is much less than the bit
rate.
Other topics in our resources on Broadband Internet related to SDSL include: