eaceful This, in turn, will eventually lead to the introduction of SDH coexistence, however, the issue is, as ever, clouded by that of equipment onto the premises of business customers. The trend to tariffing. If a 2Mbit/s circuit, delivered by SDH, is tariffed suffi- higher functional integration will probably lead to changes in PTO ciently attractively, then, for many private networks, it may be premises design because of increased heat dissipation in a given cheaper to run multiple, point to point 2Mbit/s links, rather than volume of rack space. Conclusion 42/27 42.8.2 Optical interfaces conversion is still some way in the future, hence there is no pressure to extend SDH at present. Very low cost SDH optical interfaces are expected to produce the long awaited shift in PTO station cabling from coaxial copper to 42.8.5 Memory and processing power optical fibres. There are several advantages to optical interconnec- tion e.g. relatively long range, no crosstalk, physically small calling As soon as it becomes economically feasible, more memory and volume. However, perhaps the biggest advantage is the future proof- processing power will be installed in individual SDH network ing which results from the fact that an optical interconnect cable elements. The use of this capability to support ever larger blocks of can, within reasonable limits, carry any bit rate. Besides enabling software will results in the average software download action trans- the reuse of cables that would be difficult to reuse otherwise, it also ferring ever more bytes, thus putting a strain on the Embedded reduces the problem of successive layers of interconnect cables Communication Channels (ECCs) that are built into the STM SOHs. physically preventing the withdrawal of the older, disused, cables There is also the chance that larger quantities of more sophisticated that they are burying. element control software will result in more management traffic between network elements and between elements and their control- 42.8.3 Optical amplifiers lers,