The good old telephone service has gone though many changes during its lifetime but perhaps the most significant was the move from analogue to digital, reflects Professor Nigel Linge.
Naturally, the human voice is inherently analogue but transmitting it as such makes the resulting electrical signal susceptible to the impact of noise and attenuation, leading to a reduction in overall voice quality. However, in 1938 a radical alternative technique was proposed by Alec Reeves, who was working at International Telephone and Telegraph’s laboratory in Paris.
Reeves proposed that the analogue signal should be sampled at regular intervals, with the amplitude of the voice signal being converted into a binary number and then transmitted as a series of electrical pulses. So long as these pulses could be detected at the receiver, the original analogue voice could be reproduced without degradation. Known as Pulse Code Modulation (PCM), Alec Reeves was awarded French Patent No. 852 183, on 3 October 1938 for his ideas which in effect heralded the dawning of the digital age. Unfortunately, as is often the case with pioneering ideas, the technology of the day was not capable of realising the complexity of PCM.
In fact, it was not realised until 1968 when the GPO in Britain opened the world’s first PCM exchange which was the Empress telephone exchange near Earls Court in London. This was the first exchange of its type that could switch PCM signals from one group of lines to another in digital form and it laid the foundations for the more widespread use of digital switching that now sees PCM at the heart of our fixed-line, mobile and IP-based telephony along with all our digital audio systems.
At the other end of the scale, and seemingly trivial in comparison, BT changed the way domestic telephones were connected to their network on the 19 November 1981 with the introduction of the plug and socket interface. Up until this time the telephone in your home was permanently wired to the BT network which meant that connecting a computer to the phone line could only be achieved using either an acoustic coupler or via a telephone with an integrated modem such as the Type No13A Datel modem set. The best speeds that could be obtained with such systems was typically 300bit/s. However, the introduction of the plug and socket interface in 1981 changed all of this. The telephone service provided by BT was now terminated in a ‘master’ socket into which the customer could plug their own phone.
More importantly, this meant that there was now a direct electrical connection to the external phone line which provided a more efficient mechanism for connecting a computer via a modem. In 1988 the V.21 modem increased speeds to 1.2kbit/s; in 1991 this was extended to 14.4kbit/s with the V.32 modem; and ultimately in 1998 speeds reached 56kbit/s with the V.90 modem. Thereafter the introduction of Digital Subscriber Line technology led directly to today’s superfast services and all thanks to introduction of a simple socket.
Today with 15 per cent of UK households now officially declared as mobile only, there is a slow but growing trend away from traditional fixed-line telephony. An important step on that journey was made on the 14 December 2009 when the Scandinavian telecommunications company, TeliaSonera, became the first operator to commercially launch a publicly available LTE (4G) mobile network. Back in 1981 Scandinavia had led Europe into the mobile era and now in 2009 it was leading the world into 4G deployment with services opening in the central parts of Stockholm and Oslo. The network infrastructure was provided by Ericsson in Stockholm and Huawei in Oslo and was initially targeted at mobile broadband customers using a Samsung provided LTEonly USB dongle. Proper 4G handsets took a little longer to materialise but once again Scandinavian companies led the way in Europe when the Samsung Galaxy S2 LTE became available to their customers in 2012. Later that year the UK witnessed the launch of its first 4G network. Today there are over half a billion 4G subscribers across 151 countries with, interestingly, the UK now cited as offering some of the highest average 4G download speeds in the world.