nnel capacity. This now seems a major trend on coaxial tree and branch networks in particular, only signals in with perhaps a final feed of just 3 or 4 amplifiers left. their r.f. multiplex are directly accessible; demodulation to base- The AM fibre optic links in particular have not to date been cheap; band must be performed by high quality equipment to avoid this as they reduce in cost this will help their application to become process adding significant impairment itself. Everyday analysis is wider. The advent of the optical amplifier may help here, enhancing often better carried out directly at r.f. for those parameters where it their modest optical budget and allowing optical splitting. is possible; carrier to noise (C/N) is one such measurement (with a target of 43dB upwards for a full cable TV network), and to cover second and third order intermodulation performance composite 57.3.7.5 New architectures second order (CSO) and composite triple beat (CTB) are parameters commonly used. The tree and branch structure has remained remarkably resilient and has itself made advances in increased capacity. The fibre optic 57.3.7 Future trends enhancement above will be a major change, itself creating other openings. It will naturally zone a system into areas of a few hundred This area is well served by papers in journals and conferences, and or thousands of people depending on its depth of penetration into references are given later to which the reader should turn for the network. This may then favour associating with the zone, swit- detailed information. Service possibilities have been indicated ear- ches and multiplexers for data and telephony. A hybrid network may lier, and how these are taken up will affect the technical evolution grow up mixing switched star and tree and branch concepts. significantly. The major areas of activity are likely to be as below. Instead of the point to point optical links now being installed, splitters will be introduced to share the capacity more economically (but will of course be co