Editing Packet Switch Stream (section)

== 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]] and later on, when problems of 10-100 ms transmission failures with the PCM Voice based transmission equipment used by the early [[BT Kilostream|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]] market place. The PAD service could be connected to via a dedicated [[four-wire telephone circuit]] using a PSS analog [[modem]] and later on via a [[BT Kilostream|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 float]]s. [[Logica]] (now LogicaCMG) designed the CHAPS system and incorporated an encryption system able to cope with HDLC bit stuffing on X.25 links.

===Speeds===
[[file:Kingsway tunnels -JPP 7837 (14619958901).jpg|thumb|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 ''[[BT Megastream|Megastream]]'' and ''[[BT Kilostream|Kilostream]]'' services, 2M ([[Mega-|Mega]]) bit/s and 256K ([[Kilo-|kilo]]) bit/s respectively. On analog links 2400 bit/s, 4800 bit/s, 9600 bit/s and 48&nbsp;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 [[public switched telephone network|PSTN]] 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.