The key to ADSL is that the upstream and downstream bandwidth is asymmetric, or uneven. This is known as G.lite in the ITU standards committee. As a result, the ADSL signal is carried over the entire house wiring, which results in lower available bandwidth due to greater noise impairments. HDSL has a longer range than T1 without the use of repeaters to allow transmission over distances up to 3.6km. The name has become more generic over time to refer to symmetric service at a variety of rates over a single loop.
Cable modems are devices that attach to the cable TV network connection in a residence.
There are a number of challenges faced by this industry including bi-directional data transfers as well as customer service issues and the lack of standards. However, potential bandwidth estimates range upwards of 30 Mbps from the service provider to subscriber. Cable networks are inherently different in design than telephone networks. Cable networks are broadcast oriented, with each subscriber in an area receiving the same signals - effectively a party line. There can be significant security and over-subscription issues as a result.