Packet Switch Stream (PSS) was a
public data network
A public data network (PDN) is a network established and operated by a telecommunications administration, or a recognized private operating agency, for the specific purpose of providing data transmission services for the public.
The first public ...
in the United Kingdom, provided by
British Telecommunications (BT). It operated from the late 1970s through to the mid-2000s.
Research, development and implementation
EPSS
Roger Scantlebury was seconded from the
National Physical Laboratory to the British
Post Office Telecommunications division (BPO-T) in 1969. He had worked with
Donald Davies
Donald Watts Davies, (7 June 1924 – 28 May 2000) was a Welsh computer scientist and Internet pioneer who was employed at the UK National Physical Laboratory (NPL).
During 1965-67 he invented modern data communications, including packet s ...
in the late 1960s pioneering the implementation of
packet switching
In telecommunications, packet switching is a method of grouping Data (computing), data into short messages in fixed format, i.e. ''network packet, packets,'' that are transmitted over a digital Telecommunications network, network. Packets consi ...
and the associated
communication protocol
A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any variation of a physical quantity. The protocol defines the rules, syntax, semantics (computer science), sem ...
s on the local-area
NPL network
The NPL network, or NPL Data Communications Network, was a local area computer network operated by the National Physical Laboratory (United Kingdom), National Physical Laboratory (NPL) in London that pioneered the concept of packet switching.
...
.
By 1973, BPO-T engineers had developed a packet-switching communication protocol from basic principles for an Experimental Packet Switched Service (EPSS) based on a
virtual call capability. However, the protocols were complex and limited; Donald Davies described them as "esoteric".
Ferranti
Ferranti International PLC or simply Ferranti was a UK-based electrical engineering and equipment firm that operated for over a century, from 1885 until its bankruptcy in 1993. At its peak, Ferranti was a significant player in power grid system ...
supplied the hardware and software. The handling of link control messages (acknowledgements and flow control) was different from that of most other networks.
The EPSS began operating in 1976, the first
public data network
A public data network (PDN) is a network established and operated by a telecommunications administration, or a recognized private operating agency, for the specific purpose of providing data transmission services for the public.
The first public ...
in the UK. EPSS was interconnected with
SATNET and the
NPL network
The NPL network, or NPL Data Communications Network, was a local area computer network operated by the National Physical Laboratory (United Kingdom), National Physical Laboratory (NPL) in London that pioneered the concept of packet switching.
...
.
IPSS
The
International Packet Switch Stream (IPSS) was an international network service, based on the X.25 standard, launched by the international division of BT. This venture was driven by the high demand for affordable access to US-based database and other network services. A service was provided by IPSS to this market, which started operation in 1978. IPSS was later linked to PSS and other packet switched networks around the world using
gateways based on the
X.75 standard.
IPSS was interconnected with SATNET.
JANET
Janet may refer to:
Names
* Janet (given name)
Surname
* Charles Janet (1849–1932), French engineer, inventor and biologist, known for the Left Step periodic table
* Jules Janet (1861–1945), French psychologist and psychotherapist
* Maur ...
connections were available via IPSS.
PSS
A period of pre-operational testing with customers, mainly
UK universities and
computer manufacturers, began in 1980. Packet Switch Stream launched as a commercial service on 20 August 1981 based on X.25/X.75. The experimental predecessor network (EPSS) formally closed down on 31 July 1981 after all the existing connections had been moved to PSS.
The network was initially based upon a dedicated modular packet switch using DCC's TP 4000 communication processor hardware. The operating system and the packet switching software were developed by
Telenet (later on
GTE
GTE Corporation, formerly General Telephone & Electronics Corporation (1955–1982), was the largest independent telephone company in the United States during the days of the Bell System. The company operated from 1926, with roots tracing furth ...
Telenet). BT bought Telenet's system via
Plessey Controls of Poole, Dorset who also sold Telex and traffic light systems. PSS was launched before Telenet's own upgrade of its network and, at the time, most other networks still used general purpose mini-computers as packet switches.
For a brief time the EEC operated a packet switched network,
Euronet, and a related project
Diane to encourage more database and network services to develop in Europe. These connections moved over to PSS and other European networks as commercial X.25 services launched.
Later on the InterStream gateway between the
Telex
Telex is a telecommunication
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communica ...
network and PSS was introduced based on a low speed PAD interface.
In addition, BT used Telematics packet switches for the Vascom network to support the
Prestel service.
The network management systems were based in
London
London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...
and
Manchester
Manchester () is a city and the metropolitan borough of Greater Manchester, England. It had an estimated population of in . Greater Manchester is the third-most populous metropolitan area in the United Kingdom, with a population of 2.92&nbs ...
. Packet switches were installed at major trunk exchanges in most major conurbations in the UK. Network management was run on a system of 24
Prime
A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways ...
63xx and 48xx computers running a modified versions of Revisions 20 and 22 of the
Primos operating system.
The
DNICs used by IPSS and PSS were 2341 and 2342 respectively.
The last PSS node in the UK was finally switched off Wednesday, 28 June 2006.
Description
Companies and individual users could connect into the PSS network using the full X.25 interface, via a dedicated four-wire telephone circuit using a PSS analog
modem
The Democratic Movement (, ; MoDem ) is a centre to centre-right political party in France, whose main ideological trends are liberalism and Christian democracy, and that is characterised by a strong pro-Europeanist stance. MoDem was establis ...
and later on, when problems of 10-100 ms transmission failures with the PCM Voice based transmission equipment used by the early
Kilostream service were resolved, via a Kilostream digital access circuit (actually a baseband modem). In this early 1980s era installation lead times for suitable 4-wire analog lines could be more than 6 months in the UK.
Companies and individual users could also connect into the PSS network using a basic non-error correcting RS232/V.24 asynchronous character based interface via an X.3/X.28/X.29 PAD (
Packet Assembler/Disassembler) service oriented to the then prevalent
dumb terminal
A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. Most early computers only had a front panel to input or display ...
market place. The PAD service could be connected to via a dedicated
four-wire telephone circuit using a PSS analog
modem
The Democratic Movement (, ; MoDem ) is a centre to centre-right political party in France, whose main ideological trends are liberalism and Christian democracy, and that is characterised by a strong pro-Europeanist stance. MoDem was establis ...
and later on via a
Kilostream digital access circuit. However most customers, for cost reasons, chose to dial up via an
analog modem over the then UK analog telephony network to their nearest public PAD, via published phone numbers, using an ID/password provided as a subscription service.
The current day analogy of ISPs offering broadband always on and dial up services to the internet applies here. Some customers connected to the PSS network via the X.25 service and bought their own PADs. PSS was one of the first telecommunications networks in the UK to be fully liberalised in that customers could connect their own equipment to the network. This was before privatisation and the creation of British Telecommunications plc (BT) in 1984.
Connectivity to databases and mainframe systems
PSS could be used to connect to a variety of online databases and mainframe systems. Of particular note was the use of PSS for the first networked
Clearing House Automated Payment System (CHAPS). This was a network system used to transfer all payments over £10,000 GBP (in early 1980s monetary value) between the major UK banks and other major financial institutions based in the UK. It replaced a paper based system that operated in the City of London using electrical vehicles similar to
milk floats.
Logica
Logica plc was a Multinational corporation, multinational information technology, IT and Management consulting, management consultancy company headquartered in London and later Reading, Berkshire, Reading, United Kingdom.
Founded in 1969, the c ...
(now LogicaCMG) designed the CHAPS system and incorporated an encryption system able to cope with HDLC bit stuffing on X.25 links.
Speeds
BT KiloStream equipment in a telephone exchange in 2004
There was a choice of different speeds of PSS lines; the faster the line the more expensive it cost to rent it. The highest and lowest speed lines were provided by the ''
Megastream'' and ''
Kilostream'' services, 2M (
Mega) bit/s and 256K (
kilo) bit/s respectively. On analog links 2400 bit/s, 4800 bit/s, 9600 bit/s and 48 kbit/s were offered. Individual users could link into PSS, on a pay as you go basis, by using a 110, 300, 1200/75, 1,200 or 2,400 bit/s
PSTN
The public switched telephone network (PSTN) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony. The PSTN consists ...
modem to connect a Data Terminal Equipment terminal into a local PSS exchange. Note: in those days 2,400 bit/s modems were quite rare; 1,200 bit/s was the usual speed in the 1980s, although 110 and 300 bit/s modems were not uncommon.
Investment challenges
Early years
PSS suffered from inconsistent investment during its early years. Sometimes not enough and sometimes too much but mostly for the wrong reasons. BT's attitude to packet switching was ambivalent at best. France's
Transpac had a separate commercial company with dedicated management and saw X.25 packet switching as a core offering. BT's then senior management regarded packet switching as a passing phase until the telecommunications nirvana of ISDN's 64 kbit/s for everyone arrived.
Tymnet acquisition and exchange for other assets
BT bought the
Tymnet network from
McDonnell Douglas
McDonnell Douglas Corporation was a major American Aerospace manufacturer, aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own ...
. BT subsequently exchanged major US elements of the Tymnet business with
MCI for other assets when the proposed merger of their two businesses was thwarted by MCI's purchase by WorldCom.
In the words of BT's own history:
British Telecom purchased the Tymnet network systems business and its associated applications activities from the McDonnell Douglas Corporation on 19 November (1989) for $355 million. Its activities included TYMNET, the public network business, plus its associates private and hybrid (mixed public and private) network activities, the OnTyme electronic mail service, the Card Service processing business, and EDI*Net, the US market leader in electronic data interchange
Electronic data interchange (EDI) is the concept of businesses electronically communicating information that was traditionally communicated on paper, such as purchase orders, advance ship notices, and invoices. Technical standards for EDI exist to ...
.
BT Tymnet anticipated developing an end to end managed network service for multi-national customers, and developing dedicated or hybrid networks that embraced major trading areas. Customers would be able to enjoy one-stop-shopping for global data networks, and a portfolio of products designed for a global market place.
These services were subsequently offered by BT Global Network Services, and subsequently by Concert as part of Concert Global Network Services after the Concert joint venture company was launched on 15 June 1994.
Later years
Even in later years, BT's senior management stated that the Internet was "not fit for purpose".
Investments in
value added network services (VANS) and BT's own access level packet switching hardware delayed operating profit. This in turn dented PSS's low credibility with BT's management still further. Despite healthy demand for basic X.25 services and the obvious trend for more demanding bandwidth intensive applications that required investment in more powerful switches a decision to develop BT's own hardware and network applications was made instead.
In the midst of this IBM (the then market leader in computing) and BT attempted to launch a joint venture, called Jove, for managed SNA services in the UK. And for a time significant extra expenditure was allowed for BT's data services, PSS being the major part, as one concern of regulators was this joint venture might damage work on Open Systems Interconnection. This only made cost control worse and achieving operating profit delayed further. Eventually the UK government decided the SNA joint venture was anti-competitive and vetoed it. But not before PSS management was allowed to commit to large investments that caused serious problems later.
One of the few successful value added applications was the transaction phone used to check credit cards by retailer to validate transactions and prevent fraud. It was believed that putting a packet switch in every local telephone exchange would allow this and other low bandwidth applications to drive revenue. The lesson of Tymnet's similar transaction phone that just used a dial up link to a standard PAD based service was not followed. Each low end packet switch installed added costs for floor space, power, etc. without any significant value added revenue benefit resulting. Nor were they adequate for X.25 host traffic.
Ideas such as providing a menu based interface, called Epad, more user-friendly than X.28 was proven obsolete by the advent of Windows-based clients on PCs.
As the added value services, named PSS Plus collectively, added significant costs and headcount while contributed virtually no revenue a change in PSS's management eventually resulted. While a decision was eventually made to put some of the basic network services people in senior positions and try to launch what had been developed this proved to be a major mistake. An exodus of people who were developing the value added network services helped reduce some costs. However significant on-going expenditure had been committed already to manufacture packet switch hardware and by using the very expensive Tandem computers in existing VANS. Operating profit was still not achieved and a further change in management with McKinsey consulting being called in.
McKinsey's recommendation that increasing revenue while cutting costs was required to turn around the business was duly followed by the new management and an operating profit achieved in about 1988. This rested on running PSS efficiently and cutting the VANS as much as possible. PSS was then merged with other failing business like
Prestel as it became part of a larger Managed Network Services division that was used to fix or close BT's problem businesses.
Legacy
Communication protocols
Researchers on EPSS in the UK and elsewhere identified the need for defining higher-level protocols. The UK
National Computing Centre
The National Computing Centre (NCC) was an independent not-for-profit membership and research organisation in the United Kingdom.
After the original organisation was liquidated in 2010, Redholt Limited changed its name to the National Compu ...
publication 'Why Distributed Computing', which was based on extensive research into future potential configurations for computer systems. This resulted in the UK presenting the case for an international standards committee to cover this area at the ISO meeting in Sydney in March 1977.
This work led to the
OSI reference model in 1984 and the subsequent
Internet-OSI Standards War.
Commercial
While PSS eventually went the way of all X.25 networks and was overwhelmed by the internet and more significantly the internet's superior application suite and cost model, BT did not capitalise as much as other packet switch operators by subsequent mistakes concerning the internet, Tymnet, BT's North American operations and the Concert Global Services with ATT.
BT's failure to become the major ISP in its own home market unlike every other former PTT and the success of Dixon's Freeserve, Demon and Energis based virtual ISPs in the same sector has only been recovered from recently. Only after BT changed its most senior management who were fixated on circuit switching/ISDN based on System X/Y telephone exchanges and embracing broadband/internet lock stock and barrel has this changed. An emergency rights issue also helped resolve the debt from acquiring second or third ranked old telcos style companies around the world.
Now BT appears to be inheriting a dominating position in the Global Network Services market, based on packet switching, as CSC and Reuters sell up their networks to BT. As the commodity price of IP services based in their core 21st century MPLS network to carry voice and data finally gives them the real cost efficiencies that packet switching always promised.
See also
*
Internet in the United Kingdom § History
*
Telecommunications in the United Kingdom
Telecommunications in the United Kingdom have evolved from the early days of the telegraph to modern fibre broadband and high-speed 5G networks.
History
National Telephone Company (NTC) was a British telephone company from 1881 until 1911, w ...
References
External links
Pictures of the BT PSS equipment
{{BT Group
BT Group
General Post Office
History of computing in the United Kingdom
History of telecommunications in the United Kingdom
Packets (information technology)
X.25