DSL technologies
	Standard
ADSL	ANSI T1.413 Issue 2 ITU G.992.1 (G.DMT) ITU G.992.2 (G.Lite)
ADSL2	ITU G.992.3/4 ITU G.992.3 Annex J ITU G.992.3 Annex L
ADSL2+	ITU G.992.5 ITU G.992.5 Annex M
HDSL	ITU G.991.1
HDSL2
IDSL
MSDSL
PDSL
RADSL
SDSL
SHDSL	ITU G.991.2
UDSL
VDSL	ITU G.993.1
VDSL2	ITU G.993.2

ITU G.992.3 is an ITU (International Telecommunication Union) standard, also referred to as ADSL2 or G.DMT.bis. It optionally extends the capability of basic ADSL in data rates to 12 Mbit/s downstream and 3.5 Mbit/s upstream (with a mandatory capability of ADSL2 transceivers of 8 Mbit/s downstream and 800 Kbit/s upstream). Actual speeds may reduce depending on line quality - usually the most significant factor in line quality is the distance from the DSLAM to the customer's equipment.

ITU G.992.4 is a standard for splitterless ADSL2 with data rate mandatory capability reduced to 1.536 MB/s downstream and 512 kbit/s upstream. It is also referred to as G.lite.bis.

[edit] ADSL2 Annexes

ADSL2 has multiple modes for DSL providers to offer better services for different needs. Below is a list of available features based on ADSL2 specs from the ITU standards.

Annex Version	Spec	Description
A	xDSL over POTS	xDSL service functioning over POTS.
B	xDSL over ISDN	xDSL Services running over ISDN Digital Phone services.
C	xDSL in ISDN	xDSL System operating in the same cable as ISDN as defined in ITU-T Rec. G.961 Appendix III (Currently not implemented)
D	ATU-C and ATU-R state diagrams	See Annex D/G.992.3
E	POTS and ISDN-BA splitters	See Annex E/G.992.3. For operation according to Annexes A,B and I, the G.992.3 requirements applying over a frequency band up to 1104 kHz shall be met over a frequency band up to 2208 kHz.
F	ATU-x performance requirements for region A (North America)	F.1 Performance requirements for operation of ADSL over POTS (Annex A) F.2 Performance requirements for operation of All Digital Mode ADSL (Annex I) F.3 Performance requirements for operation of ADSL over POTS with extended upstream bandwidth (Annex L)
G	ATU-x performance requirements for region B (Europe)	G.1 Performance requirements for operation of ADSL over POTS (Annex A) G.2 Performance requirements for operation of ADSL over ISDN (Annex B) G.3 Performance requirements for operation of All Digital Mode ADSL (Annex I) G.4 Performance requirements for operation of All Digital Mode ADSL (Annex J) G.5 Performance requirements for operation of ADSL over POTS, with extended upstream bandwidth (Annex L)
I	All Digital mode POTS	Extending ADSL band to use the voice frequency range, 32 upstream tones for an additional 256 kbit/s upstream data rate over POTS lines.
J	All Digital mode ISDN	Extending ADSL band to use the voice frequency range, 64 upstream tones for an additional 256 kbit/s upstream data rate over ISDN Lines.
L	Reach Extended	Increases the range of the DSL service enabling the link to work at a distance of 7 kilometers, or 23000 ft
M	Increased Upload speeds	Upstream/downstream frequency split has been shifted from 138 kHz up to 276 kHz, allowing maximum upstream bandwidth to be increased from 1.4 Mbit/s to 3.3 Mbit/s.

[edit] See also

• ADSL
• ADSL2+
• List of device bandwidths

[edit] External links

• ITU-T Recommendation G.992.3 : Asymmetric digital subscriber line transceivers 2 (ADSL2)
• ITU-T Recommendation G.992.4 : Splitterless asymmetric digital subscriber line transceivers 2 (splitterless ADSL2)
• ADSL2 & ADSL2+ White Paper (PDF) (Aware)

This article related to telecommunications is a stub. You can help Wikipedia by expanding it. v • d • e