SHDSL (Symmetric High bit rate Digital Subscriber Line) is an open standard for
symmetric DSL installations over one or two metallic pairs at payload data
rates ranging from 192 to 2304 kbps for one pair or from 384 to 4608 kbps for
two pairs.  Its advantage over SDSL/2B1Q (see the ../SDSL directory on this
site for the latter) is that it's an open standard at least in theory; the flip
side however is that it's significantly more complex and the existing practical
implementations of all that required complexity are anything but open.  (In
other words, the signal format spec is nominally open, but are you going to
make your own chip?  If you are, you would have to implement a DSP and a framer
significantly more complex than for SDSL/2B1Q.  Two different framers actually,
read the spec for the details.)

Other advantages though are that SHDSL is said to have superior speed/distance
performance and has proper support for repeaters.

Note that in Europe (covered by ETSI) the acronym "SDSL" is used to refer to
the scheme more unambiguously known as SHDSL, rather than to 2B1Q SDSL as found
in USA.  IFCTF uses the term SHDSL exclusively to avoid ambiguity; for us SDSL
most often means SDSL/2B1Q.

This directory contains the ETSI version of the S(H)DSL spec and documentation
and other materials for some of the available chips that implement this
standard.  We currently have some materials for Orion from Conexant (formerly
GlobespanVirata), for M289xx from Mindspeed (formerly Conexant) and for some
Infineon chips.  All 3 companies are very secretive and shitty.

If you know of any other currently available SHDSL chips, please let us know
and we'll list them too.