ly. Ethernet support-The latest ADSL2 standard includes a packet mode transmission convergence layer (PTM-TC), which supports packet-based services such as Ethernet. ADSL2+ The ITU-T approved ADSL2+, or ADSL2plus, as G.992.5 in 2003. ADSL2+ doubles the downstream frequency band to 2.2MHz, increasing the DMT channel count to 512. This effectively doubles the maximum downstream data rates, achieving up to 24Mbps on phone lines as long as 1 mile (1.5km) while supporting up to 1Mbps upstream. However, under most practical scenarios, speeds are in the 15Mbps to 20Mbps range when delivered approximately 1 mile (1.5 km) from the local exchange. DSL Technology ADSL2+ solutions are most commonly multimodal, interoperating with ADSL and ADSL2, as well as with ADSL2+ chipsets. There is also an option in which cus- tomers served by digital loop carriers could be designated to operate only on the higher frequency channels (i.e., 1MHz to 2.2MHz) to limit interference with cus- tomers on longer loops who would be assigned the regular ADSL/ADSL2 channels (i.e., <1.1MHz). ADSL2+ allows service providers to evolve their networks to support advanced services, such as video, in a flexible way, with a single solution for both short-loop and long-loop applications. ADSL2+ includes all the feature and performance ben- efits of ADSL2 while maintaining the capability to interoperate with legacy equip- ment. The other major enhancement with ADSL2+ is improvement in crosstalk and interference control. The standard specifies a set of upstream and downstream power spectrum density (PSD) masks that define methods for shaping the DSL transmission signal. Particularly important on longer loops (i.e., 2.5 to 3.5 miles [4 to 5.5 km]), the PSD masks allow the modems to optimize performance by adjusting the power levels on the various DMT channels. The operator can specify which mask to use when the link is installed, or the modems can determine which mask to use in the initialization and handshaking. Some telcos are already beginning to use ADSL2+