Goodbye to something that didn’t exist … Location 23
Goodbye to something that didn’t exist … Location 23
A few years ago, BT invited me to give a keynote talk at one of their research open-day conferences. The location? Well, it was a secret place that no one should know that it exists … the BT Tower in London. After my talk, I was invited to take the lift to the top floor and was shown the whole of London’s landscape. Coming from Edinburgh, it always amazes me how flat London is, but it gives amazing views of all the famous landmarks. “And, do you know, Bill, that we are actually moving?”, “Are we?”, “Yes, fix on a building, and watch it”. And, yes, we were moving. It was fantastic.
Cryptography, The Internet and Telecommunications
There are three great things that I love in the history of technology. The first is the creation of public key encryption and with all the advances of the 1970s, 1980s and 1990s. It is a story of Diffie and Hellman; Rivest, Shamir and Adleman; Merkle; and so many others. And, the story of the creation of the Web is another, with the creation of Ethernet, routers, HTTP and all the other protocols and methods that created this amazing technological advancement. But, the third thing is the rise of telecommunications, and where we moved from a voice network that struggled to support 64 kbps to now supporting many gigabits per second.
BT
And, at the root of telecommunications in the UK, is one company: British Telecommunications. This mighty company grew from the Post Office, and managed to build a massive voice-focused network and then migrated it to a digitally focused network. The BT Tower was created in 1964 and was always seen as the iconic home of the company. At one time it had 57 microwave dishes and supported radio communications across the cities, in the days before cellular networks. Now it is being sold to MCR Hotels for £275m. Why did they sell it? Well, apart from being an iconic building, it does not serve a great purpose for BT. Its customer focus is on its EE brand.
In fact, the Tower was at the core of a national telecommunication network and was defined as an official secret. In a court case, the tower could not be named, and only defined as ‘Location 23’ (although, it did appear in Ordnance Survey and London A-Z street maps).
From Strowger switches to System X
I remember, as a child, marvelling through the window of a telephone exchange seeing an array of Strowger switches performing their switching of voice calls:
But, BT saw the future and invested in 1979 in the System X exchange. This was a great time for me, as I studied communication engineering in the 1980s, so I was able to see the rise of digital switching. The work involved a collaboration of great UK companies such as GEC, Plessey and STC, and which saw the first System X exchange in 1980 (Baynard House, London). While the Strowger switches required the mechanical movement of switches, the digital exchange did it with transistors. These new exchanges allowed for new functions, such as call back and call barring. By the mid-1980s, System X was providing the main trunk services between the major cities in the UK. System X then became System Y, and further accelerated the advancement of digital switching.
64 kps and above
The problem these exchanges solved was to move analogue signals into a digital form. This typically happened by sampling audio at Nyquist’s rate, and where we needed to sample the voice signal at twice the highest frequency of the audio signal. As voice quality, at that time, supported up to 4kHz, the sample rate was 8 kbps. If we define that each sample is represented with 8 bits, then we have a base rate of 64 kbps — known as PCM (Pulse Code Modulation). With this, System X would time-multiplex the data samples into larger frames, which were multiplexed up to 32 lines into a 2 Mbps frame (32 x 16 kbps). This was known as an E1 frame. Now, a single line could support 32 incoming calls. This could then be multiplexed up again for trunk routes.
And, through the 1990s, BT continued to scale up and speed up the network, and where the UK (possibly) led the world in its communications infrastructure. The company, though, had many challenges, including moving away from the untwisted pair of copper cables which connected to homes — the “last mile connection”. The advent of the modem allowed citizens to transmit digital information over voice-focused networks and with the “super speed” of 56 kbps. If you were lucky, you could have a special digital ISDN connection, and which allowed for two data streams of 64 kbps. This ISDN network allowed for digital data to be transmitted into the network without converting it into an analogue form.
On 11 March 1998, the UK network became fully digital. The next challenge was to upgrade the wires and cables to a level that could support not kbps but Mbps.
Conclusions
So, well done to BT for scaling their network infrastructure. For me, I now have a larger bandwidth potential at home than I have at work. For the BT Tower, it is the end of an era. I still love telecommunications, and I will never take for granted the ability to walk about a city and be able to transmit video.
