2. ADSL2+
Over the past few months, Alan and I have attended a couple of ADSL2+ workshops presented by Alcatel (now Alcatel Lucent) with expert presenters from Alcatel Belgium.
The aim of these workshops was to bring us up to speed on ADSL2+, and also for us to brief Alcatel on the scope of the new ADSL2+ PTC spec which we have asked them to provide input for. We have just received the first draft from Belgium, and hopefully over the next month or so we will get it to the point where we can publish a draft for public comment.
On the surface ADSL2+ looks similar to ADSL1 with additional downstream data capacity due to extending the frequency range from 1.1 to 2.2 MHz. However there is a lot more sophistication in both the diagnostic data collected by the modem and DSLAM, and also the handshake between them. For example the modem and DSLAM both measure the signal to noise ratio and request transmit powers to be altered for optimum performance. Importantly this includes lowering the powers on short loops in order to lower the noise floor in the cable, thus giving customers further out on the same cable a better chance of obtaining reasonable speeds. ADSL2+ modems are also better at dynamically reacting to changes than their predecessors.
All DSL technologies are limited by fundemental limits of data capacity in the presence of noise outlined in the famous paper in the late 1940s by Claude Shannon. In practice this means that the higher speeds are only available on relatively short loops, and normally by about 4km and beyond ADSL1 and ADSL2+ deliver similar speeds. Even higher speed DSL technologies such as VDSL are really only worthwhile up to a few hundred metres, and are often used in appartment buildings feeding high speed data to occupants from a fibre terminal in the building.
Christmas Greetings
Another year of Telepermitting has passed with an increasing flow of products over a wide range of technologies. Voice over IP components have increased (again) by 25%”, cordless phones up 20% have been amongst the most prevalent this past year. Broadband modems have remained steady (at about one per week), and Corded telephones have made a comeback with over double the number being Telepermitted this year compared to last year.
It remains for Alan and me to wish all our readers a very Merry Christmas and Happy New Year.
Richard Brent
Access Standards
