Reread my previous message: I said "upstream"
and "upload speed".

DSL accesses are most often asymetric (so the acronym ADSL). SDSL (symetric) is deployed mostly for professional accesses, but still very rare at a competitive price for home users.

Cable users have also an asymetric speed due to the shared physical link.

In Europe, most [b]up[b]stream speeds for ADSL are between 64kbps and 128kbps, even for accesses up to 2Mbps downstream. There are some newer offers to get 256kbps upstream, but SDSL is still not economically competitive for home users.

Remember that the total bandwidth available on a POTS line is the sum of the POTS or ISDN service (4kHz), plus 2 times the bandwidth in bits per second, of the uptream and downstream width.

So for a 1024/128 kbps ADSL link, the total bandwidth used will be (1024+128)*2+4 = 2308 kHz. There's in fact a required gap of at least 4kHz between the POTS and the DSL channels, which are chosen by subchannels of 4kHz each and multiplexed in parallel.
A 1024/128 ADSL link uses 256 channels of 4 kHz, chosen in a set of channels available in a band of about 3Mhz-wide (which offers 768 channels). The number of usable channels in this band depends on the POTS line physical properties: total lengths, quality, attenuation, diaphony, etc...

The DSL technic allows determining automatically which 4 kHz channels are the best to use to offer the connection. Each channel offers 2kBps of raw binary bandwidth, generally used with a ATM framing protocol (which uses small 64-bytes frames with small control headers, and fixed sizes, called "cells", which allow easy resynchronization and quality control). One cell is fully transported on a single channel, so multiple cells can be sent in parallel on distinct channels.