Packet Switch Stream

Packet Switch Stream (PSS) was a public data network in the United Kingdom, provided by British Telecommunications (BT).

He had worked with Donald Davies in the late 1960s pioneering the implementation of packet switching and the associated communication protocols on the local-area NPL network.

[1][2][3][4] 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.

The network was initially based upon a dedicated modular packet switch using DCC's TP 4000 communication processor hardware.

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 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).

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 market place.

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.

Investments in value added network services (VANS) and BT's own access level packet switching hardware delayed operating profit.

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.

It was believed that putting a packet switch in every local telephone exchange would allow this and other low bandwidth applications to drive revenue.

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.

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.

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.

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.

[17] 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.

An emergency rights issue also helped resolve the debt from acquiring second or third ranked old telcos style companies around the world.

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.