Do you always read the small print? If you do not, there may well be some disappointments in store for you. That is especially the case when you order broadband DSL access via a landline. Journals, forums, and blogs are full of complaints from ­customers who have simply overlooked or ignored the words – naturally in very small print – “up to”. Some network operators have been known to go overboard in marketing the maximum data rate that is theoretically possible, i.e., based on the technology being used. How great then is the disappointment when only a fraction of the promised speed is realized. Just imagine the reaction if this sort of thing happened after you bought a car. You are unable to achieve more than half of the promised top speed, maybe even less (on an empty highway without speed limits, of course) – unthinkable!   

Similar phenomena are familiar from mobile networks; the first generation of broadband systems fell well short of expectations. Why is it that the promised speeds are often not achieved with so-called “high-speed” Internet access? Is it the car or the road – after all, we have to accept the limits imposed by the latter when driving every day – or both? The answer to this question is not quite so simple because there are various possibilities depending on the technology being used. This is why we have to talk about reach as well as speed.    

The candidates on stage   

Let’s start with the technological variant for broadband access which is the easiest to explain, fiber optics. In this case, car and road cannot be beaten when it comes to transmission speed – regards from Michael Schumacher. The lucky few who have this kind of connection do not waste a single thought on the ­question of speed. The physics behind the transmission medium and the optical transmission technology  enable speeds in both PTP (point to point) and PMP (point to multipoint) configurations which are far above the requirements of today’s services and represent a secure investment for the future. The principle of optical transmission is based on today’s digital, i.e., time and value discrete, modulation of the intensity of a suitable source (laser) which, due to the short wave lengths, leads to extremely short rise times. This is equivalent to a high transmission bandwidth: using today’s technology, 40 Gbit/s can be achieved. As long as the signals are adequately coherent, the transmission capacities can be multiplied almost infinitely through frequency multiplex – key words here are WDM and DWDM.