Dave Burstein's excellent DSL Prime

Dave Burstein’s excellent DSL Prime newsletter reports on a new technology called Dynamic Spectrum Management that promises to increase the speed of DSL technologies substantially. The cool thing is that it works the same way as some of the efficiency-enhancing dynamic sampling techniques now being developed for unlicensed wireless connections:

John Cioffi and T1E1.4 have just reported on DSM, technology that will often double speeds. First results were with short range VDSL, confirmed now for ADSL and G.shdsl in many, but not all, environments. By monitoring the actual binder conditions (including what other modems are active, change in external interference, etc.), the DSL modem can change the bit loading (number of bits and gains on each bin) from the transmitter, transmission power and other factors. Modems on short loops can reduce power to enable longer reach on other lines.

ADSL+ uses improved computation and makes some tradeoffs to get improved speed over short distances. Current work is bringing efficiency close to the theoretical Shannon Limit for a standard noise profile. If that noise model is accurate, physics will soon prevent any further improvement. DSM goes further, adjust for different noise patterns in real life binders, which vary over time. This allows the modem to be “tuned.” for actual rather than assumed noise patterns. In addition, multiple pairs bonded together can get a more than proportionate increase in throughput. This will allow multiline G.shdsl to surpass 10 meg symmetrically over copper.

Wired or wireless, the important revolution is that the devices on the network are getting smarter. The transport mechanism matters, but ultimately it will recede into the background.