Thursday 7 November 2019



by David Riddle

This article appeared in the November 2001 GIHS Newsletter

It struck me recently that there are aspects of our 'Industrial History' that remain active even today.  I am referring to the fact that at least one of the London Borough of Greenwich's main employers has roots going back a very long way, with the achievements of its predecessors, both company-wise and personnel-wise frequently the subject of discussion in this Newsletter. The particular organisation I am thinking of is Alcatel.

Alcatel took space to run quite a large corporate stand at October's Crown Wood's School Vintage Car Fair, which this year incorporated an Industrial Heritage Fair and an event called Sci'Tech 2001.  Alcatel have an active education unit that supports the teaching of science in schools, and their stand incorporated large-scale maps of their current cable network as well as computer systems demonstrating cable manufacture.  Heat-sensitive cameras provided instant colour print-outs of all the hot-spots in your brain or other parts of one's anatomy that you thought were properly out of sight and out of reach!

In the same week, Alcatel, a French-owned multi-national, had announced significant job losses at its Christchurch Way plant, previously known as STC Submarine Systems.  This was surprising as, indeed, has been the recent apparent general downturn in the telecommunications market, so I took the opportunity to ask one of the staff on duty for some inside information on his views of the reason for the current problems.  What I learnt was quite an eye-opener.

One might think from all the hype that the vast majority of telephone and data traffic these days, especially Internet traffic, goes by satellite?  This is not true.  Some 85% of all inter-continental traffic uses cable, not satellite.  One of the reasons for this can be witnessed on the current nightly TV News videophone links from inland Afghanistan.  There is a significant, and sometimes very annoying, delay in the reception of data when transmitted by satellite.  In contrast there is no such delay with cable.  Voice data takes a mere 0.003 sec. to travel from one side of the Atlantic to the other.  Satellite is a much more important and significant carrier from locations within continents, but even this dominance is being challenged by huge investment in terrestrial cable.

An interesting fact revealed by Alcatel's maps was that submarine cables no longer just link continent 'A' to continent 'B'.  There is now a major infrastructure of cables that circumnavigate the major continental landmasses.  As examples, cable now go right around Africa and South America, with nodal points offshore that provide links to the major cities around the coast.

When the first long-distance cables were manufactured and laid in the mid-19th century, there were numerous problems to be overcome.  The cables themselves were made of copper and extremely heavy.  The ships that carried them were still often made of wood and subject to severe weather conditions for which they were much less well equipped to deal with than their iron and steel successors.  Cables were often lost overboard in storms, involving huge project delays and weeks of painstaking work with grappling irons to find the lost 'end' in thousands of feet of water, work that was not always successful.

Also, remember what's down there on the seabed.  It's an exact equivalent of what there is above water level.  Plateaus, hills, huge mountain ranges, everything in fact that you can think of terrain-wise.  Where do the cables get laid?  Do they always follow exactly the same path, or does each one follow a well-surveyed route?  It seems that similar, but not identical paths are followed, but it is neither technically possible, nor advisable to lay one cable exactly parallel to another.  Most modern systems are actually designed as loops.  Two shore base stations on either continent are linked by a continuous loop of cable that also links the shore stations.  The sections of submarine cable may be separated by several hundred kilometres.  If some kind of disturbance of either a man-made or natural variety were to affect one cable it would not affect the other arm of the loop, so services would only suffer a break of a few tens of milli-seconds while switching of traffic to the undamaged cable occurs.  Cables apparently also end up following the lie of the land.  If one were to imagine trying to lay a fairly rigid chunk of cable over even a modest set of mountains such as in the Lake District, it should be obvious that this cannot always occur, so there will always be short lengths of 'suspension', although the geologists involved aim to keep these to a minimum, otherwise they would thrash around too much in the underground currents and possibly snap.

Cables have always required insulation to avoid the nasty effects of the potential mix of salt water and signal-carrying metal.  One of the first innovations to come out of the Enderby Works was that of the use of a material called gutta-persha, a far superior insulator to anything that had gone before it.  Nowadays this has been superseded by the use of polythene, which is virtually non-degradable.  Furthermore, you will no longer find data cables made of copper manufactured for the long-distance transmission of voice and data traffic.

All cables laid prior to 1988 were copper co-axial and carried analogue signals.  In that year the first trans-Atlantic digital optical fibre cable, called TAT-8, came into operation.  This cable consisted of a pair of optical fibres, one for transmission in each direction, along which signal-carrying beams of light travel.  These light beams carry the voice/data 'channels'.  Early cables required powered 'regenerating repeaters' at regular intervals along their length.  As much as 10KVolts was needed to supply a constant 1 amp of current to the 100 or so repeaters on a typical 7500km trans-Atlantic cable.  This power was carried along a copper sheath which lay outside the fibres and inside any protective armour that may have been required to provide additional protection for the cable in the particular environment it was designed for.  

These repeaters convert weak incoming optical signals to electrical signals, amplify that signal, and then convert it back into optical form for transmission along the next section of cable.  It was not until 1996 that the first systems using full optical amplification came in to use.

However, whereas with copper, it was fundamentally only possible for a single strand of copper to carry a single voice channel, although this could be improved by a process called multiplexing, with optical fibres the same fibre can be made to carry multiple channels through the use of different laser light wavelengths.  This results in a huge increase in the overall capacity of the cable.  Only five years ago the standard number of wavelengths in use in submarine cables was 4, with 40 being deployed on some terrestrial cable systems.  Today it is 16 with 100 coming on stream, and at higher transmission speeds, another developing factor.  The result is that the same original cable can potentially carry at least 100 times more data.  Some estimates are that it may be possible to increase this number to 1000 within the next few years, and there are also options to increase the number of fibre pairs from the common standard of only 4 in trans-Atlantic cables to 16.  This would require a consequent increase in the size of optical repeaters, and this might in turn require prohibitively expensive modifications to the 30 or so cable-laying ships that currently provide the laying and repair capability for the world's submarine cable network.

Perhaps you are beginning to understand the nature of Alcatel's current problem?  Although demand for more and more capacity in optical cables has been existence for many years, there come points in time when demand is temporarily met, yet the technology marches on.  This is driven by business competition which, ironically, starts to become contrary to the interests of those same businesses.  Optical cable doesn't need replacing as frequently as copper, so once laid, a cable will function quite happily for its planned operational life of 25 years.  Capacity is met, cable become ever more capable, and sales start to drop off.  This is the problem Alcatel currently face.

As the man said, the telecomms industry is a bit like a roller coaster.  At this point in time Alcatel appear to have simply become almost too good at their own game!  If you are interested to learn more at a fairly high, but still remarkably readable level, try; An Oversimplified Overview of Undersea Cable Systems.  David O. Williams.  Information Technology Division.  European Laboratory for Particle Physics (CERN)  

No comments: