er than technology opportunity. The adoption of neutral host networks covered in the third part of this book is an example of this process at work. The technology case for a neutral network managed by one entity but accessed by many has been obvious for some time. It is simply an extension of the fundamental principle of multiplexing gain. The concept is, however, only recently gaining market traction. The reason for this is that data demand is increasing faster than technology capacity. Technology capacity is substantially different from network capacity. As demand increases across any delivery domain, wireless, cable, copper or fibre, it is technically possible to increase network capacity simply by building more infrastructure. Existing capacity may also be underutilised, in which case life is even easier. However, if infrastructure is fully loaded additional capacity is only financially justifiable if revenues are growing at least as fast as demand or at least growing sufficiently fast to cover increased operational cost and provide a return on capital investment. Technology can of course change this equation by increasing bandwidth efficiency. The transition to digital for example yielded a step function gain in bandwidth efficiency that translated into profitability, but as systems are run ever closer to fundamental noise floors it becomes progressively harder to realise additional efficiency gain. This is problematic for all sectors of the industry but particularly challenging for wireless where noise floors are determined by a combination of propagation loss and user to user interference. Present mobile broadband networks provide a dramatic illustration. Mobile Broadband Traffic Growth Forecasts and the Related Impact on Industry Profitability In a study undertaken last year4 we forecast that over the next five years traffic volumes would grow by a factor of 30, from 3 to 90 exabytes. 5 On present tariff trends we projected revenue to grow by a factor of 3. On the basis of the data available since then, p