Faraday Consultancy Limited
Faraday Consultancy Limited (FCL) is a private limited company registered in England and Wales, Company Registration Number 2938426, owned and managed by Chris Angove.

When the plain old telephone service (POTS) was the white heat of technology, sometimes you would find a telephone kiosk in an apparently remote country area. With advancing technology and mobile communications, most of these have gone now. Before de-regulation local residents could apply for a telephone kiosk in their area. A survey would be made of how many local residents already had a (very expensive) telephone line and if that was more than a government agreed percentage, the application would be declined. This one was probably between remote communities with relatively few existing subscribers.

Blog: DOCSIS, ADSL, Fibre, Mobile Broadband

I wrote the blog at the bottom of this page some 8 years ago, so it is well overdue for an update. There have of course been many changes in telecommunications over the last few years so there is plenty to write about.

There have been interesting evolutions in terminology. The word 'wireless' today as an adjective has had a renaissance following its earlier adoption well into the twentieth century, both as an adjective and as a noun. Some of us will remember a smart, veneered wooden box in the corner of the room, designed to look like a piece of furniture and using valves (vacuum tubes), the radio technology of that era, which we called 'The Wireless'.

'Wireless' of course means 'no wires' and today is still accurately used as an adjective, but usually for relatively short range communications perhaps serving just a handful of nodes and typically under the control of the telecommunications consumer like you or I. We probably would not describe mobile (digital cellular) or satellite as wireless, but they are of course. These represent big infrastructure investments and employ technologies, the results of international collaborative efforts by large telecommunications operators, manufacturers and regulatory authorities. Probably the most popular of the wireless technologies today would be WiFi, an abbreviated name for 'Wireless Fidelity'. Perhaps a slightly strange adoptation, the idea coming from HiFi for High Fidelity, which audiophiles will be familiar with. WiFi, which started life as IEEE 802.11 in about 1985, has been updated many times. WiFi has been designed as a high capacity wireless networking standard as a potential replacement for the wired alternative, Ethernet, itself derived from IEEE 802.3. Ethernet has also been updated many times over the years and has both copper and optical fiber versions. WiFi and Ethernet both use packet technologies.

The wireless standard Bluetooth, in this case starting as IEEE 802.15.1, is now managed by the Bluetooth Special Interest Group and includes smaller capacity options than WiFi or Ethernet. This is one of the 'low rate wireless personal area networks', together with IEEE 802.15.4. If the high data capacity of something like WiFi is not actually required, the Shannon Nyquist capacity theorem allows the bandwidth and/or power to be reduced thus enabling more channels and potentially reliable communications over greater distances.

All of these wireless technologies are unlicensed and use frequency bands allocated to unlicensed equipment, also described as Industrial, Scientific and Medical (ISM). Here 'unlicensed' means that the user or operator does not need to get a licence to use it, but nevertheless the hardware has to meet the necessary electromagnetic compatibility (EMC) requirements specified by the regulatory authorities. Those of us who like hacking things unfortunately have to refrain from doing this with ISM equipment because that would render them non-compliant.

Digital cellular (mobile) communication technologies have now evolved up to what is generally considered to be the fourth generation (4G) and also referred to long term evolution (LTE). LTE itself has evolved to LTE advanced (LTE-A) and no doubt there will be further evolutions in the future years and 5G is starting to roll out.

I can confirm that the client I visited 8 years ago can now get a 3G mobile broadband but, better than that, he now has a DOCSIS (broadband) cable connection. This was part of an investment initiative to bring broadband to remoter parts of the UK. He is located about 6 km from the (former) telephone exchange which was a very long distance for ADSL, effectively making it unusable. It appears that the telecommunications operator has installed fibre optic lines from the telephone exchange, with a considerable distance overhead, strung across poles. Perhaps we should call them fiber poles. (That is a guess on my part because when I was in the area recently I saw notices on the poles to the effect that they were not carrying copper conductors, perhaps directed at potential scrap metal thieves). Even before fiber optics most of the nearby cables in and out of these little exchanges were underground so there was probably duct capacity available for fibre optics.

I need to sidetrack a little here. When I talk about 'telephone exchanges', that name is rather out of date now. The small rural telephone exchanges that I am referring to were typically about the size of a small garage and located around small population centres. They were used originally to provide the telephone circuit switched routing (exchange) service for local subscribers, part of the national PSTN (public switched telephone network). Today, few countries still use circuit switching, it being replaced in the digital era by packet routing technology. In the UK, many of these small telephone exchanges were built by 'The Post Office' around the mid-twentieth century. The Post Office was nationalised and, despite its name, was also responsible for the telecommunications of the era, very much a minor offshoot of its postal services empire which generated much more revenue. In the course of de-regulation the former telephone exchanges have been inherited by various telecommunications service providers.

When I was young lad out on my bicycle in a rural part of Cornwall sometimes I would find these garage-like structures and wonder what they were all about. I thought they were something to do with telephones but, looking around, there were usually few, if any, telegraph poles and wires visible. Although we used to call them 'telegraph poles', their more correct name was 'telephone poles'. The wires near teh exchanges were of course underground. Because of the large number of telephone wire connections required close to the exchange, the necessary dense clusters of telegraph poles and associated wire pairs would not have been welcome in a scenic area.

In those days relatively few people could afford the cost of renting a telephone line, not to mention the call charges. There were many more public telephone kiosks than today and the location of the closest kiosk was often a major factor in making the decision. The thought of more than half an hour's walk on a wet and windy winter's night to the nearest kiosk, perhaps to then need to wait in a queue, was a popular theme of the Post Office advertisements.For those of us who live in or near urban centres we may have a broadband internet connection provided by broadband cable, usually just referred to as 'cable' or colloquially as cable television (CATV). Alternatively we might have digital subscriber line (DSL), usually asymmetric DSL (ADSL).

By cable we usually mean an evolution of CATV in which a cable service provider makes a (copper coaxial) cable connection to the customers' premises. Originally, to provide the broadband data service, the cable actually carried digitally modulated information over some of the bandwidth as well as the original (analog) television services. More recently, all of the available cable bandwidth has been digitally modulated to maximise the 'bandwidth' which may be rented to the customer. In fact with most cable providers the value of the TV channels was so small compared to all but the slowest broadband that customers were effectively 'forced' to take it and probably ended up watching rather too much junk-TV.

The specifications which regulate broadband cable are known as the 'data over cable service interface specifications' (DOCSIS) and were originally drawn up by Cable Television Laboratories (Cable Labs) in the USA where CATV was pioneered.

ADSL uses the same pair of wires that was originally used for the analog telephone connections to the local telephone exchange but modified as far as possible to carry digital modulation. Whilst ADSL refers to the generic service, it is often available in the various forms of enhanced services. For example, ADSL2 and ADSL2+.

CATV was originally designed to provide a reliable distribution of analog receive-only television channels to neighbourhoods via cables using frequency division multiplex (FDM) and therefore not involving any potentially unreliable radio wave propagation. The CATV infrastructure provided appreciable 'downstream' bandwidth ranging from around 50 MHz to an upper band edge of between 300 MHz and 870 MHz, depending on the level of service provided. DOCSIS services use bandwidth sections of these cables to carry digitally modulated data streams using various types of (usually quadrature amplitude) digital modulation. They also provide for data transmission in both directions: downstream and upstream; their proportions determined by the degree of asymmetry of the connection. Data is carried over DOCSIS broadband cables using digitally modulated carriers as opposed to any form of 'baseband' services. The provision of a broad bandwidth digital baseband over a cable designed for CATV was not adopted because:

To provide the digital broadband services in the downstream direction, from the cable head to the customer's premises, the available cable bandwidth is split up into channels each with a bandwidth of around 6 MHz to 8 MHz. Each channel is then used to carry a digitally modulated carrier using, typically, 64 or 256 quadrature amplitude modulation (64QAM or 256QAM). Every cable broadband customer is supplied with a cable modem to interface the local network, usually via Ethernet or universal serial bus (USB) on the customer side, an RF coaxial connection on the cable company's side.

In many countries, the regional broadband cable infrastructures are owned by individual companies, or service providers. At any one location there may not be another competing broadband cable provider. Unfortunately, in a de-regulated telecommunications environment, people living in remote areas are less likely to have competing service providers, so often have to pay high charges for rather pedestrian speed services. The early installations of broadband cable services are usually therefore in urban and suburban areas.

The original analog telephone service built up by PSTNs over many years across the World since the invention of the telephone is often rather accurately called the plain old telephone service (POTS).

When the original telephone lines were installed, most of them were overhead as this was much cheaper and simpler than burying them in the ground. The capacitance between the two wires carrying the 'go' and 'return' currents was compensated for by periodically adding series inductances, known as loading coils. However, these too were only designed for very low frequencies with bandwidths of around 3kHz to 4kHz which was sufficient for basic voice telephony. In more recent years, advances in high frequency component design has enabled economic conversion of these lines to ADSL. ADSL exploits the available bandwidth of the remaining line itself, without loading coils. The original audio section of the bandwidth is separated out using filters at both ends of the line and retained for a POTS telephone connection, usually supplied as a package 'bundled' with the broadband service. The upper part of the frequency band is split into 4312.5 Hz segments, the greater the available bandwidth, the more segments will be possible. The ADSL modem is designed to detect the segments that are workable and use digital modulation over them. The available bandwidth for ADSL is the aggregate of all of the workable segments after making some allowances for overheads. As the connection was not originally designed to be wideband, the line usually becomes heavily absorptive as its length increases