Dear all,
There was a time when computers were linked together in networks using
packet-switching exchanges. One protocol for such exchanges was the X.25,
or, as it became known in the Scandinavian countries, Datapak. It was
particularly telecom companies, such as the Norwegian Televerket, later
privatised and rebranded as Telenor, that had an interest in X.25. Indeed,
it was their work to make it known under the Datapak nomen.
The specificity of X.25 was it's mechanism to ensure there no faulty
packages would be delivered. At the heyday of X.25 lines (cables, but also
good, old analogue 'phone connections) were not as reliable as we've gotten
used to today, X.25 demanded that each node in the Wide Area Network would
verify and return faulty packages. Due to it's precision and rigour in the
face of insecure hardware, it is still in use today, mostly in automated
teller machines and credit card payment terminals. The architecture ensured
that every transmission was correct; however, as packages could not exceed
1024 bytes, and since the protocol generally regarded seven packages to
constitute the limit of a transmission, it wasn't any longer appropriate
with the advent of the internet and large data transmissions.
The Swedish Televerket introduced the name Datapak for it's commercial X.25
service in 1985. It was delivered by Tymnet, and based on proprietary
hardware of the so-called Engine family. In Sweden it was the American
company McDonnel Douglas that delivered X.25. Through their office in
Bromma Sweden was linked to the American network through a permanent (i.e.
not dial-up) modem connection, which had the at the time astounding speed
of 64kbit/s.
Today most data transmission is based on end-to-end verification. However,
did we not lose something on the way from X.25 to IP: was it not beneficial
that faulty packages would be intercepted and returned before delivery?
Mvh. / Yours sincerely,
Torgeir Fjeld
https://torgeirfjeld.com/
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