Back in the day

From murder most foul to Integrated Services Digital Network and 3G, January, February and March have seen some extraordinary highlights in the telecommunications world, says Professor Nigel Linge.

On 1 January 1845 John Tawell entered a chemist’s shop and bought some Scheele’s Acid, a treatment for varicose veins that contained hydrogen cyanide. He travelled to Salt Hill near Slough where he met his mistress, Sarah Hart, whom he then proceeded to poison with the acid. Sarah’s screams and cries for help were heard by a neighbour but John ran off and made his way to Slough railway station where he boarded the 7:42pm train to London Paddington. Unfortunately for John, Slough and Paddington stations had been fitted with a Cooke-Wheatstone two needle electric telegraph system.

Sarah Hart’s neighbour raised the alarm and the local vicar pursued John to the station where he asked the Station Master to signal ahead to Paddington and alert the Police. However, the telegraph system could not send the letters J, Q or Z which created problems because the vicar said that John was dressed like a Quaker! The word Quaker had to be sent as Kwaker which caused the telegraph operator at Paddington great consternation in understanding it; even after retransmission. Eventually the message was handed to Sergeant William Williams who was given the task of tracking down and arresting John. At his trial, The Times newspaper reported that, ‘Had it not been for the efficient aid of the electric telegraph, both at Slough and Paddington, the greatest difficulty, as well as delay, would have occurred in the apprehension’. John Tawell was hanged at 8am on Friday 28 March 1845 and thereafter became known as ‘The Man Hanged by the Electric Telegraph’.

tel2The electric telegraph was the country’s – and the world’s – first data network. Of course data in that sense was the written telegram and the network never reached into our homes. However, with the emergence of the home computer and our onward drive towards digitisation came a demand for public data networks for both business and domestic consumers. In response to this on 7 February 1991, BT launched their Integrated Services Digital Network (ISDN) service. Originally developed in 1988 by the CCITT (ITU), ISDN provided a digital connection comprising two symmetric bi-directional data channels (2B) each operating at 64kbit/s and a 16kbit/s signalling channel (D). This basic rate 2B+D service offered much higher data rates over its competitor technologies and proved especially popular with the broadcasting industry where the guaranteed data rate with its low latency was ideal for high quality voice and music transmission.

BT developed and marketed its ISDN service as Home Highway but in 2007, withdrew it from domestic customers because of the rise in the popularity and capability of xDSL broadband access. As of 2013 there were still 3.2 million ISDN lines in the UK but this number is falling year on year. Within Europe, ISDN was most popular in Germany where at one point they accounted for 20% of the global market.

Delivering data into the palm of your hand offered a different challenge but took an important step forward on 3 March 2003 when the first mobile network to offer a 3G service was launched in the UK by a new entrant into the mobile marketplace. Telesystem International Wireless (TIW) UMTS (UK) Limited had the backing of Hong Kong based Hutchison Whampoa but soon Hutchison bought out TIW to create H3G UK Limited which, having acquired spectrum from the infamous UK 3G auction, marketed its new service under the more familiar ‘Three’ brand. Choosing to launch their service on 3/3/3 was therefore an opportunity not to be missed! Quite how much network coverage was available at that time remains a point of conjecture. Nevertheless, the UK had entered the 3G world with the first public 3G call being made by Trade and Industry Secretary, Patricia Hewitt, who called Stephen Timms, Minister for e-Commerce.

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Three launch devices: NEC e606, Motorola A830 & NEC e808

The move to 3G brought with it the promise of higher data rates and at the time of launch, Three offered its customers a choice of three different handset options, the Motorola A830, NEC e606 and NEC e808. As is often the case, these first generation handsets were actually poorer than their predecessor technology being bulkier and suffering from poor battery life. That aside, by August 2004, Three has connected one million customers.

This article first appeared in The Journal, Volume 10, Part 1 – 2016. The Journal is free to all ITP members, to find out about joining visit our website

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Packet versus voice switching

The prevailing view is that moving voice to an IP solution gives many advantages, especially cost. What are the economic arguments for switching voice calls in packet rather than circuit mode, putting to one side the technical and quality-of-service issues?

Some inter-related themes form the big picture of telecommunications networks today:

• The big architectural difference between circuit and packet-switched networks is the location of the service control – within the network with circuit-switched, at the edge with packet-switched. Control at the edge and use of an essentially dumb packet network enables ‘over the top’ service providers, such as WhatsApp, Skype, FaceTime, to have the commercial relationship with the users.

• There is a growing sentiment that always-on access to the Internet is a basic human right. Unfortunately, there is a tendency also to devalue content, insofar as people do not care to have to pay for it.

• Many network operators are considering how best to replace their circuit switches forming the PSTN. Replacement by IP systems has proved difficult and many operators are waiting to take advantage of the shift of voice away from the fixed PSTN onto mobile. Despite this, the fixed PSTN is still essential in most countries as a network of last resort and for interconnection.

On the question of whether packet is cheaper than circuit switching for voice, there are several points to consider:

  • Switching system costs – Many would say that packet switching is cheaper – after all, many supported services are free. Often overlooked though is the price users pay for the infrastructure supporting voice over Internet Protocol (VoIP) – the computer/tablet/smart phone, broadband access and Internet Service Provider service, etc. Therefore, the question is whether there is any inherent cost (as opposed to ‘price’). Interestingly, there is remarkably little difference between the elements of a circuit switch-block and those of an IP router; both usually comprise time-space-time switch with similar semiconductor technology. So, apart from differences in the costs of signalling, the inherent costs are essentially equal.
  • Terminating functionality – A profound influence on all network costs is the location of the interfacing equipment. Terminating a line on the exchange represents some 70% of the total cost of the switching system, costs incurred by the network operator. However, for VoIP services, the analogue-to-digital encoding, packetisation, powering, and ring-tone generation is in the users’ devices (a computer or tablet), the costs of which are borne by the user giving a cost advantage to VoIP providers. However, if a fixed operator hopes to use VoIP to replace its circuit-switches and if many of its users wish to keep their telephone and line, the operator will have to provide the terminating functions at the boundary of the packet switching system. Mobile operators do not have this concern as mobile handsets provide the functionality.
  • Multi-service platform – A single all-purpose platform supporting all services has long been seen as a way of saving capital and operational costs. This advantage is true with any technology, not just IP (indeed, earlier multiservice platforms were circuit-based).
  • Bearer traffic loadings – The potential loadings of 85% or higher with packet networks compare favourably to about 70% in circuit-switched networks. However, such loadings on packet networks are avoided to reduce the probability of packets being delayed, particularly for latency-intolerant services such as voice. Lo 30% is typically required to ensure voice quality, so reducing any cost advantage of packet switching.
  • Industry economies of scale – There is a general move towards the use of IP technology for networks as there is with computer-controlled digital electronics in general. Since vendors’ prices are driven by economies of scale, today’s prices of packet switching benefit from this shift – which rather makes the economics of circuit versus packet switching a self-fulfilling prophecy.
  • On a like-for-like basis, therefore, there is no inherent cost difference between circuit and packet-switching technology. However, packet can benefit from the shift of the user network interface and the move to a multi-service network. The enthusiasm of fixed operators to move to VoIP has slowed because of the need to support existing fixed subscriber lines. The UNI location is not an issue for mobile networks; existing 4G networks will shift to all-IP architectures as the existing circuit-switched mobile exchanges are withdrawn.

This is an executive summary of the full article which appeared in The Journal, Volume 10, Part 1 – 2016. The Journal is free to all ITP members, to find out about joining visit our website

The need for synchronisation in telecommunications

Synchronisation in telecommunications largely arose from the introduction of 64kbit/s digital switching and transmission of voice telephony. For digital switching to work, it is critical that the sampling, coding, multiplexing and switching all occur at exactly the same rate. If samples arrive at the switch more often than they can be written then at some point a sample must be thrown away; and if samples arrive less often then at some point the same sample will be repeated. Either of these will result in an audible disturbance. Hence each piece of equipment in each exchange must run at the same rate (or frequency), and from this arises the fundamental need for synchronisation.

Rather than providing separate infrastructure for distributing synchronisation, the Primary Rate bit-stream at 2048kbit/s was adopted. However these bit-streams do not have a wholly repetitive and predictable pattern of edges from which to recover the reference frequency. Such short-term variations (or jitter) in frequency that accumulate along a chain of nodes in the hierarchy are smoothed out by means of a high quality oscillator and a long time-constant phase locked loop.

Increasing traffic demanded more capacity which was met, in part, by multiplexing the Primary Rate bit-streams into higher and higher bit rate transmission paths. However, these Primary Rate signals may not be synchronous with each other and, to cater for the differences, the old Plesiochronous Digital Hierarchy (PDH), used a technique known as justification whereby dummy bits are either added (or not) to equalise the bit rates. This approach means that the synchronisation borne by a Primary Rate input signal is carried transparently and independently in the multiplex (although some jitter may be introduced by the justification).

Synchronous Digital Hierarchy (SDH) multiplexing largely replaced PDH. SDH uses a byte-interleaved scheme to multiplex and cross-connect the payloads of the SDH signals. However, it cannot be assumed that the payloads are synchronous with the overall SDH frame, and even other SDH frames may not be synchronous (for example they may originate within another operators network). To cope with this, SDH has a justification method in which a pointer is included in the overheads to indicate the start of the payload within the frame, allowing the payload to ‘float’ within the SDH multiplex structure. SDH still uses a 125 microsecond frame, and so the synchronisation rate and interfaces are carried over from PDH.

The emergence of IP telephony and softswitching had been hailed as the beginning of the end of the need for synchronisation. However, cellular mobile networks had quietly been taking advantage of existing synchronisation infrastructure for a quite different purpose, and is now probably the dominant user of frequency synchronisation.

Digital cellular base stations have tight limits on the frequency of their carriers and frame repetition rates in order that mobile devices can successfully decode signals from different nearby base stations and seamlessly move between them during calls. Early base stations achieved this using costly high stability oscillators. However, the transmission to these base stations uses the same Primary Rate signal as described above and this is used as an accurate frequency reference. The signals do suffer from jitter but this can be smoothed out by a relatively inexpensive oscillator locked to the incoming transmission.

More recently, base stations began using Ethernet-based transmission; it is mandatory for 4G and now common for 3G and 2G as well. Therefore the delivery of synchronisation was incorporated into the Ethernet standard to create Synchronous Ethernet (SyncE). An alternative to SyncE is Precision Time Protocol (PTP), a method for transferring time over packet networks. PTP has some advantages over SyncE in that it can be implemented on pre-existing Ethernet networks but is sensitive to packet delay variation.

The LTE-Advanced base station air interfaces will require alignment in time (with submicrosecond accuracy) as well as frequency so that mobile devices can sort out the signals from different base stations. Time synchronisation can be achieved via the transmission or from an off-air source such as GPS. None of the available methods is without challenge and much of current work on synchronisation is focused on solving these.

This is an executive summary of the full article which appeared in The Journal, Volume 10, Part 1 – 2016. The Journal is free to all ITP members, to find out about joining visit our website

Spotlight on: women in IT

Women make up under 30% of the information and communications technology (ICT) workforce, and only 15.5% of the science, technology, engineering and mathematics (STEM) workforce.

Increasing the number of women working in information technology (IT) could generate an extra £2.6 billion each year, according to a report from the Select Committee on Digital Skills*. But there are a number of stumbling blocks – notably education and careers guidance – which need to be overcome.

The Chartered Institute for IT (BCS), notes the report, found that of 4,000 students who took computer science at A level, less than 100 were girls. The University and Colleges Admissions Service, meanwhile, found that in 2014, 17,300 more men than women entered computer science, and 20,300 more men entered engineering. In both of these fields men made up over 85% of acceptances.

This is an interesting affirmation of a 2013 ONS (Office of National Statistics) report which found male graduates in the UK earning an average of £3 more per hour than women. The ONS found that of the top five subjects associated with the highest average gross annual earnings, ‘four of them were subjects which male graduates are more likely to have studied than female graduates’. And the subjects? Engineering, Physical/Environmental Sciences, Maths/Computer Science and Architecture.

One of the main difficulties in attracting women to digital and STEM occupations would appear to be their perception as largely male-dominated roles and that tech roles are often seen as ‘jobs for the boys’. Compounding this is a misconception of what digital and STEM jobs are in reality. As the Select Committee’s report points out, the range of jobs is huge and varied (see below). The Select Committee’s findings are that the current lack of women in digital and STEM is holding back UK competitiveness: “We agree with our witnesses that increasing the numbers of women could reap significant benefits. Girls have to be engaged earlier and across all education levels. The perception of digital and STEM jobs and subjects as male-orientated must be addressed.”

EXAMPLES OF NON-TRADITIONAL STEM PROFESSIONS

  • Computer animator – computer animation generates animated images by using computer graphics. It can include: computer visualisation; computer animation arts; and digital effects.
  • Cosmetic chemist – a cosmetic chemist formulates cosmetic products such as shampoo, skin cream etc.
  • Forensic scientist – forensic skills are used in areas including archaeology, food and engineer pharmaceuticals, criminal justice and at disaster scenes.
  • Forensic engineering: is the investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property.
  • Architect – architects now use digital tools to generate and evaluate design and fabricate complex assemblies.
  • Electrical engineer – an electrical engineer on, for example, the railway uses latest design software systems and state of the art technology to develop train design. They will also work on live dynamic testing simulated on the computer and in test facilities.

Following on from the first ITP Women in Telecoms Award, Telecoms Professional spoke with three different women in three very different roles for their take on women in the industry. You can read the full article here 

 *Select Committee on Digital Skills. Make or Break: The UK’s Digital Future, 17 February 2015 Full Report