adsl2/2+ FAQ

The 11 Most Frequently Asked Questions About ADSL2 & ADSL2+ Answered

ADSL2 and ADSL2+ technologies have enabled ISP providers to provide their customers with high-speed broadband via legacy copper lines.  We’ve compiled a list of  the 11 most commonly asked questions about ADSL2 & ADSL2+ to demystify the Digital Subscriber Line (DSL) technologies. If you’re interested in learning more about VDSLs, visit our VDSL/2 FAQ here.

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1. What is ADSL2/ADSL2+?

ADSL2 and ADSL2+ are DSL technologies that deliver high-speed broadband using Plain Old Telephone Services (POTS). Copper telephone wires consist of at least 25 or more twisted wire pairs making transmission signals susceptible to crosstalk. ADSL2 and ADSL2+ utilize sophisticated modulation technologies to eliminate noise and interference in transmission signals. This allows for relatively error-free transmission via legacy copper lines.

2. How fast is ADSL2?

Actual speeds vary depending on networking environments and copper loop lengths. ADSL2 can achieve downstream data rates of up to 12 Mbps speeds at its source while ADSL2 can achieve up to 24 Mbps. ADSL2/2+ are best suited for longer loop lengths. ADSL2 can reach distances of up to 5,000 meters while ADSL2+ can achieve up to approximately 6,000 meters.

Refer to the chart below to compare ADSL2, ADSL2+, and VDSL2 speeds.

ADSL2/2+ vs. VDSL Speed Comparison Chart

3. What is the farthest ADSL2/2+ can reach?

ADSL2 can reliably support high-speed broadband to loop lengths as far as 5,000 meters while ADSL2+ can achieve slightly longer distances at 6,000 meters.

4. What are some ADSL2 improvements?

ADSL2 improves:

  •         Modulation Efficiency
  •         State Machine Initialization
  •         Coding Gain
  •         Signal Processing Algorithms
  •         Framing Overhead Reduction
  •         Seamless Rate Adaptation (SRA)

Seamless Rate Adaptation (SRA) allows the transceivers to adjust transmission rates according to changing networking conditions in real-time. SRA is a functionality that allows ADSL2 to decouple packets in the modulation layer while maintaining the framing layer parameters intact. This preserves the synchronicity of the information transmitted while modulation rates are adapted.


5. Are ADSL2/2+ DSLAMs energy-efficient?

Yes. Most ADSL units provide consistent power feeding which not only wastes energy and resources but also increases heat dissipation which can damage equipment after prolonged usage. ADSL2 provides two energy-efficient power modes: L2 and L3 low-power modes to help conserve energy.  The L2 low-power mode can adjust power based on the traffic demands of an individual-per-use-case. ADSL2 units will kick into full power mode during traffic intensive applications such as occurs when downloading large files and revert back to L2 low-power mode when the surplus power is no longer necessary. The L3 low-power mode puts the transceiver at the Central Office (CO) to sleep after a period of inactivity.  

6. How does ADSL2/2+ achieve high data rates?

One of the features that enables ADSL2/2+ to achieve high data rates is channel bonding. ADSL2/2+ has the capacity to bond several telephone phone lines together to achieve higher bandwidth. ISPs can bond several channels to achieve a wider bandwidth and increase downstream and upstream data rates. Channel bonding resembles the process of adding more lanes to a freeway so that it can support more traffic. This flexibility enables Internet Service Providers (ISPs) to offer different tiered data rate services to subscribers.

7. Are ADSL2/2+ units compatible with previous versions of ADSL2?

Units with the “ADSL2 fallback” feature provide support for previous versions of ADSL standards. Units will revert to previous standards if connected to devices that support older standards so as to preserve compatibility.  

8. What is the difference between ADSL2/ADSL2+?

ADSL2 and ADSL2+ are variations of the same technology. ADSL2 utilizes frequencies between .14 MHz and 1.1 Mhz. ADSL2+ offers double the frequency range, between .14 Mhz and 2.2 Mhz. The wider channel bandwidth of ADSL2+ doubles its downstream data rates.

ADSL2+ technology also has the capability of eliminating crosstalk. Since ADSL operates between the .14 to 1.1 Mhz frequency range, ADSL2+ will automatically transmit signals on the 1.1 to 2.2 range to prevent crosstalk. This functionality is especially useful when both ADSL2 and ADSL2+ services are present in the same binder on course to a customer’s premises.

9. What is the difference between Annex A vs. Annex B?

ADSL over POTS, more commonly known as Annex A, is used in North America. Europe on the other hand, utilizes Annex B which delivers ADSL over ISDN.  Annex A and Annex B provides approximately  24 D / 1.4 U Mbps rates.

10. What is the difference between Annex A vs. Annex M?

Also known as ADSL2 M and ADSL2+ M, Annex M provides a slight improvement in upstream rates when compared to Annex A. Annex M yields up 3.3 Mbps upstream data rates as opposed to the typical upstream rates of 1.4 Mbps in Annex A.

11. How old are the ADSL2/ADSL2+ standards?

The G.992.3 and G.992.4 ADSL2 standards were introduced in July 2002. The G.992.5 ADSL2+ standards received official standardization in 2003.

Did you know that copper lines can now transmit gigabit speeds in laboratory settings? Find out more about the up and coming G. Fast technology here.