lml, Re: DSLx3 ... I suspect someone there just "discovered" IDSL, the poor relation of the xDSL family that uses the ISDN line code (2B1Q) and therefore does not exhibit the immutable distance limitations of DMT or CAP modulation. The physics of xDSL establish two primary degrees of freedom: data rate and reach. When anyone crows about a breakthrough on one, it is always appropriate to ask about the other. IDSL basically has the data rate of ISDN, depending on the exact implementation, either 128 or 144 kb/s. This is really a different animal than the other xDSL flavors.
There are some relatively new implementations of 2B1Q line code "modem pairs" that have reduced the power requirements, and therefore, increased the possibility for powering remote span 2B1Q repeaters. This could be the "new information" you are being told of.
The key to remember about the distance range of ADSL, whether it be a CAP, DMT, or g.lite(subset of DMT) implementation, is that repeaters don't work. Repeaters that can extend the range of IDSL are advertised to be good out to >50kf. The rub is that there would be significant loop conditioning on such a cable pair to make IDSL work, primarily removing load coils, a "rearrangement" that requires engineering and construction attention; it is not an inexpensive installation matter. I would expect to see unloading of long pairs occasionally for installation of HDSL (another 2B1Q line code member of the xDSL family)when it is used by the ILEC to provide a tariffed T1 service, because that will be compensatory at ~$600+ per month plus non-recurring installation charges. It seems much more unlikely that several hundred dollars would be spent in loop conditioning for a ~$50 per month service. Of course, as of now, each ILEC makes these calls in part as a policy decision.
Note that HDSL uses 2 pairs to deliver a quality T1 service over a potentially quite long range. The new (not quite yet standardized) HDSL2 will be a technology that can deliver a T1 service over a single pair without interference to other xDSL services in the same cable. That is a big deal. However, HDSL2 gets away from 2B1Q to accomplish that, and the overlapping shaped pulse amplitude modulation signals that HDSL2 use will not be repeaterable. The range of HDSL2 will probably be ~15kf, less than HDSL. Once available from vendors, HDSL2 will probably take over the lion's share of that market, with long copper loops the sole stronghold for the older HDSL 2-pair technology. |
