ADSL

Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional modem can provide.

For conventional ADSL, downstream rates start at 128 kbit/s (though a minimum offering of 512 kbit/s is more common) and typically reach 8 Mbit/s within 1.5 km (5000 ft) of the DSLAM equipped central office or remote terminal. Upstream rates start at 64 kbit/s and typically reach 128 kbit/s or 256 kbit/s but can go as high as 1024 kbit/s. The name ADSL Lite is sometimes used for the slower versions.

A newer variant called ADSL2 provides higher downstream rates of up to 12 Mbit/s for spans of less than 2.5 km (8000 ft). More flexible framing and error correction configurations are responsible for these increased speeds. ADSL2+, also referred to as ITU G.992.5, boosts these rates to up to 24 Mbit/s for spans of less than 1.5 km (5000 feet) by doubling the downstream spectrum upper limit to 2.2MHz. ADSL2/2+ also offer seamless bonding options, allowing lines with higher attenuation or lower signal to noise (SNR) ratios to be bonded together to achieve theoretically the sum total of the number of lines (i.e., up to 50 Mbit/s for two lines, etc.), as well as options in power management and seamless rate adaptation — changing the data rate used without requiring to resynchronize.

ADSL service providers may offer either public or static IP addressing. Public addressing is preferable for people who may wish to connect to their office via a virtual private network, for some Internet gaming, and for those wishing to use ADSL to host a Web server.