THE ADSL2 FAMILY
Overview
as ADSL popularity grew, it begun spreading
world-wide and clearly became the carriers, service providers and
subscribers choise of broadband media. Their feedback, along with rising
demand for improvments, contributed to the completion of a new family of
standards named ADSL2. These, beside offering higher rates, are
more user-friendly for subscribers on one hand, and more profitable to carriers
on the other hand. In addition, most ADSL2's modems are backward
compatible and support the simple ADSL, making it easier to step into the next
level when upgrading.
As said before, ADSL2 isn't a single protocol but rather a family of several protocols, developed over time; each one offers improvements over the others in certain loop and noise conditions. The following sections will desribe in detail some of the main and more familiar members in the family: the basic ADSL2 over POTS (ADSL2 annex A) which defines the backbone for the new family of standards, improveming performance and interoperability in regard to the old ADSL, as well as support for new applications. ADSL2+ improves the data rates of ADSL2 achieving rates of 20Mbps over phone lines as long as 5000ft, while RE-ADSL2 increases the perimiter of the service making it accessible to more consumers sitting at the end of long telephone lines, far from the CO . Finally we will discuss Bonded ADSL2/2+, which combine the power of several lines of ADSL2/2+ into a single powerful line capable of delivering great data rates over pretty long distance.
How can we choose the best configuration
for a connection between a certain consumer and the CO? Well, one of
ADSL2's characteristics is being almost entirly automated, and here is no
different.
A new feature called "Automode" enables service providers to give their
customers the optimal level of service, by analyzing the line condition and
gathering variuos information during connection between the CO and the customer premise, and
then choosing (automatically) the best line configuration.
Figure 1. Automode in
action. The CO detects on initialization that the line to the CPE is too long for conditional ADSL2/2+.
Also, the consumer doesn't require extremely high speed services such as HD video,
and so automode decide to connect via RE-ADSL2 for optimum results.
