ugh to ensure a Mid-Fibre Meet between equipment from is, however, also possible to use other interconnection media, in two different manufacturers. G.957 recognises this problem and particular radio transmission. The problem in using radio intercon- specifies the relevant physical parameters for a range of standard nection is that, unlike optical fibres, the available spectrum is finite, optical interfaces, at the preferred SDH rates of STM-1, STM-4 and and in short supply. The liberal use of overhead capacity in SDH STM-16. In addition, there is also an extension to the existing G.703 only exacerbates the already difficult problem of squeezing the electrical interface specification to accommodate an electrical pres- traffic information into the existing arrangement of radio channel entation of an STM-1 signal. Despite this, there is still no guarantee bandwidths. These problems are by no means insuperable, but they of anything beyond traffic path interworking, as the management do tend to restrict radio interconnection of NNI signals to the lower channels that flow across the mid-fibre boundary may still be end of the SDH range e.g. up to STM-2 at present. This inability to carrying information which is unintelligible to the network man- match the transmission capacity of optical fibres will progressively agers on the other side. This is an important area that the standards force radio based systems out of the core areas of transmission bodies are still addressing. networks, and into the more peripheral areas. In particular, it is likely that radio based SDH equipment will be heavily used for 42.4.9 SDH network elements access duties. The reduction in cost that accompanies a network element with Because traffic routing flexibility is one of the reasons for the restricted connectivity results not only from simpler hardware, but existence of SDH, the simplest way of considering any SDH net- also from simpler control software. This is somewhat surprising at work element is as a group of transport termination funct