veral new features and functions, all aimed at improving perfor- mance and interoperability, while adding support for new applications, services, Chapter 12 Broadband Access Alternatives and deployment scenarios. The key changes include improvements in the data rate and reach, rate adaptation, diagnostics, and standby mode. ADSL2 supports higher data rates of up to 12Mbps downstream and 1Mbps upstream, depending on loop length and other factors. It also improves the reach by about 600 feet (180 m). ADSL2 introduces a number of features, including power cutback capability (i.e., two power modes that help reduce overall power consump- tion while maintaining ADSL's always-on functionality for the user); reduced fram- ing overhead; better modulation efficiency (i.e., seamless rate adaptation [SRA], which allows modems to signal one another in the event of changing transmission conditions and adjust the data rates almost instantaneously); channelization capa- bility (i.e., the ability to split bandwidth into different channels with different link characteristics for different applications); and bonding of lines (i.e., joining of sev- eral copper pairs to create one logically larger pipe). ADSL2 also defines an optional "all-digital mode" where the voice transmission band (<25KHz) can be used to pro- vide an additional 256Kbps of upstream transmission capacity. Other features of ADSL2 include the following: Integrated diagnostics-Extensive diagnostic capabilities greatly enhance ADSL2 transceivers, incorporating tools for trouble resolution during and after installation, performance monitoring while in service, and upgrade qualification. Faster startup-A fast startup mode reduces initialization time from about 10 seconds to less than 3 seconds. IMA-ADSL2 addresses the growing demand for even higher data rates via the ability to combine several ADSL connections, commonly referred to as bonding. Inverse multiplexing can be used to bond up to 32 ADSL links, although in actual practice bonding 2 or 3 lines is far more like