ITU G.992.5 (also referred to as ADSL2+, G.dmt.bis+, and G.adslplus) is an International Telecommunication Union standard for asymmetric digital subscriber line (ADSL) broadband Internet access. The standard has a maximum theoretical download speed of 24 Mbit/s. Utilizing G.992.5 Annex M upload speeds of 3.3 Mbit/s can be achieved.
ADSL2+ extends the capability of basic ADSL by doubling the number of downstream channels. The data rates can be as high as 24 Mbit/s downstream and up to 1.4 Mbit/s upstream depending on the distance from the DSLAM to the customer's premises.
ADSL2+ is capable of doubling the frequency band of typical ADSL connections from 1.1 MHz to 2.2 MHz. This doubles the downstream data rates of the previous ADSL2 standard (which was up to 12 Mbit/s), and like the previous standards will degrade from its peak bitrate after a certain distance.
Also ADSL2+ allows port bonding. This is where multiple ports are physically provisioned to the end user and the total bandwidth is equal to the sum of all provisioned ports. So if 2 lines capable of 24 Mbit/s were bonded the end result would be a connection capable of 48 Mbit/s download and twice the original upload speed. Not all DSLAM vendors have implemented this functionality. ADSL2+ port bonding is also known as G.998.x or G.Bond.