ECOC 1975 - ECOC 2013

might have to be spread over 20 years, during which period further
developments in detail are likely. The essential attraction of
fibres over metal conductors for cable TV would be the elimination
of intermediate electronics and the saving of cable size and cost,
while providing a network as flexible in principle as the local
telephone network. Before any decision can be taken to begin investment
in such a new network, it will be necessary to establish, by
means of field trials, that the technical problems of manufacture,
installation, operation and repair can be satisfactorily and
economically solved. Perhaps the main challenges here remain in the
manufacture of fibre cables having low and stable enough loss and
dispersion characteristics, in their pulling into ducts and/or laying
in the ground in lengths of about 2 km without significant change of
characteristics, and in jointing and terminating the fibres in
sufficiently rugged and stable yet compact and cheap \'1ays. In addition
LED's or lasers of adequate performance and demonstrated reliability
must be manufactured.
152
The last series of challenges must also be met, though probably with
different specification limits, for "junction" and "trunk" systems,
lasers rather than LED's being essential for the latter. The market
for each of these is much smaller than that for cable TV, because
(a) the essential function of the exchanges (of which there are about
6000 in the UK) is to concentrate the traffic into much fewer circuits,
and (b) the junction and trunk networks are already well developed
and new provision is needed only to cater for new growth of traffic.
The median length of junction system in the UK is about 4 times that
for prospective cable TV systems, but the market for fibres for the
former might be only about 1%of that for the latter. The median
length for trunk systems is about 100 km in the UK, but because of
the further concentration of circuits (by time-division-multiplexing)
on the trunk systems the market for fibres there is likely to be
similar to that for the junction network.
HEFERENCES
1 • Telecommunication Statistics 1974, UK Post Office Telecommunications
Headquarters TMS5.2, London.
2. Telecommunication Statistics 1973, Union Internationale des
Telecmmnunications, Geneva.
3. Local Distribution - A Time for Change? A G Hare , paper read
to Institution of Post Office Electrical Engineers, London,
March 1975.