.8 Mbits/s on the upstream and 12 Mbits/s on the downstream but the practical capacity/distance constraints reduce this to 8.448 Mbps at 9000 feet, 2.048 Mbps at 16 000 feet or 1.544 Mbps at 18 000 feet. The ADSL 2 standard G992.3 was ratified in 2002 and is similar to ADSL 1 except that the downstream can be extended below 138 kHz to provide an enhanced upstream of 3.5 Mbps. The ADSL2+ standard G.992.5 was ratified in 2003 with upstream bandwidth extended to 12 MHz to support 512 subcarriers. The headline data rates are 2.3 Mbps for the upstream and 24 Mbps for the downstream. VDSL1 (very high bit rate digital subscriber line) ratified in 2003 but the more comprehensive G993.2 VDSL2 standard was completed in 2006. The various iterations of both standards are described as profiles. VDSL1 was specified for 8- and 12-MHz operational bandwidths extended in VDSL to include frequencies up to 17 and 30 MHz. The profile number denotes the bandwidth and the letter denotes the power that is determined by whether or not the VDSL service overlaps other services. For example, a reduced power is needed in some circumstances to mitigate crosscoupling effects. The 30-MHz option also supports wider channel spacing, 8.625 kHz rather than 4.3125 kHz. Table 2.9 lists the profile and power outputs and the subsequent table shows the ADSL and VDSL band plan. 20 plain old telephone service. Physical Layer Connectivity Table 2.9 VDSL 2 profiles Profile Bandwidth (MHz) 8.832 8.832 8.832 17.664 Number of subcarriers (tones) Carrier spacing 4.3125 4.3125 4.3125 4.3125 4.3125 4.3125 4.3125 8.625 Line power dBm +17.5 +20.5 +11.5 +14.5 +14.5 +14.5 +14.5 +14.5 Higher power, for example over +20 dBm, will increase power consumption as the line driver will require a higher bias current to deliver the higher voltages needed on the line. The higher power outputs also require more linearity, which is harder to achieve over wider operational bandwidths. For example, the 8b option above with +20.5 dBm of power is downstream limited to 8.5 MHz operati