 further increasing the load on the existing ECCs. Thus, at some point in the future is very likely that the SDH standards will have to be altered to expand the capacity of the ECCs beyond their current Erbium doped fibre amplifier technology has made great strides in rates of 192 and 576kbit/s. the last three years. By using such amplifiers at both ends of an optical link, it is possible to greatly increase the maximum distance between transmitter and receiver, with distances up to 300km being predicted for links that employ low loss optical fibre cables. (c.f. Conclusion present day optical inks at 565Mbit/s which can typically span 40-70km). This great increase in span capability holds out the SDH is here to stay as the dominant public network transmission prospect of interconnecting the majority of large centres of popula- standard of this decade. However, the effects of the full range of tion in Europe by unrepeatered line systems i.e. the line systems SDH standards will probably be felt over a much wider area of consist of two LTEs plus cable, without any intervening simple telecommunications, because of their general applicability. For repeaters. (Drop and insert repeaters are a different case, as they are example the mere existence of the SDH optical interface specifica- deployed to drop and insert traffic, rather than solely to boost the tions will probably lead to their use in a variety of non-SDH amplitude of the optical signals). The resulting extinction of con- applications, simply because there is a dearth of competing stand- ventional line system repeaters means that the SDH RSOH in the ards. Another example is that of the SDH network recommendation- STMs will eventually become redundant for terrestrial systems. S, G.SNA1/2, which, with relatively little modification, are In addition to this, there is also the future proofing that results applicable to a wide variety of non-SDH networks, in particular, from replacing a conventional, electronically regenerating repeater, plesiochronous networks. wit