4 ms·

> x25 was a network where the terminals are dumb and the network needs to be smart. At the time that was a common statement, but I fail to see why X25 mandates

> x25 was a network where the terminals are dumb and the network needs to be smart. At the time that was a common statement, but I fail to see why X25 mandates dumb terminals. However a profound difference was that X25 used streams whereas TCP uses packets. A stream is akin to a TCP socket. It is a fundamental difference that stems from the fact that a X25 data exchange is safe from errors. https://farsite.com/X.25/X.25_info/X.25.htm https://farsite.com/X.25/X.25_info/X.25.htm

philprx 6y ago
It’s true that most applications were stream oriented, and Minitel was, as the users’ sessions were only bytes (in videotex encoding) rendered by the Minitel as a serial terminal integrating a modem (1200 bauds reception, 75 bauds emission!). There was a smart gateway node that translated complex x25 from the Minitel service providers nodes into simple bidirectional stream of bytes to the Minitels, it was a specialized type of packet asssembler disassembled (PAD) called a PAD Videotex (PAVI). Now x25 did have packets, Minitel terminals did not. So the PAVI and x25 servers were working very differently and with more complexity (hence smart) than Minitel serial terminals (hence dumb). It’s not that x25 mandated dumb terminals.
- non-entity 6y ago
  Haha. I've been "working" on an X.25 implementation on a PC and it took me an embarrassingly long time to figure out what the hell a PAD was ever needed for.
  - icedchai 6y ago
    My understanding 30 years ago was a "PAD" was the TCP/IP equivalent of a "terminal server", translating serial streams to network connections. This may be an overly simplistic view, I don't know. It's been a very long time! Are there any public x.25 networks still operating?
    - non-entity 6y ago
      > Are there any public x.25 networks still operating? Not that I know of. My plan if to use old line simulators and other tools i can find on ebay and telcom equipment reseller sites to create a "fake" private one. This is one of those projects that I'm working on purely out of novelty interest :P.
      - icedchai 6y ago
        Sounds cool! Perhaps you could create the x.25 equivalent of HECNet, the hobbyist DECnet.
rjsw 6y ago
OSI could run over X.25. As you say, it doesn't mandate dumb terminals. I worked for a couple of startups that ran services over X.25. One road not taken could have been to define a structured document format in ASN.1 that would be displayed by the terminal.
eternalban 6y ago
You are confusing connection-oriented phase of x.25 with “streams”. X.25 is a “packet-switched” “connection-oriented” protocol. [which p.s. makes sense for traditional telecom’s view of the world, which as you know is circuit-switched. One of the main beefs of telcos in regards to IP was traffic management. Compare X.25 congestion management with IP. ] Some kind soul has delved into the details of modalities of networking protocols: https://stackoverflow.com/a/43543284 https://stackoverflow.com/a/43543284
C1sc0cat 6y ago
I think its more correct to say x.25 was virtual circuit based - over a packet based system. x.25 had a MFT (Metric Fuck Ton) of error checking (at each layer). I used to work in OSI based networking - debugging OSI issues was an art - no wireshark back then However You could do some cool things with osi based networking binary attachments natively supported, years before the internet had it. Interworking between legacy system like Telex, I used to have my own telex number and answerback and could have had an x.400 email address at the country level. Ps id take site you linked with pinch of salt no mention of PAD's for example.

philprx 6y ago

It’s true that most applications were stream oriented, and Minitel was, as the users’ sessions were only bytes (in videotex encoding) rendered by the Minitel as a serial terminal integrating a modem (1200 bauds reception, 75 bauds emission!). There was a smart gateway node that translated complex x25 from the Minitel service providers nodes into simple bidirectional stream of bytes to the Minitels, it was a specialized type of packet asssembler disassembled (PAD) called a PAD Videotex (PAVI). Now x25 did have packets, Minitel terminals did not. So the PAVI and x25 servers were working very differently and with more complexity (hence smart) than Minitel serial terminals (hence dumb). It’s not that x25 mandated dumb terminals.

non-entity 6y ago
Haha. I've been "working" on an X.25 implementation on a PC and it took me an embarrassingly long time to figure out what the hell a PAD was ever needed for.
- icedchai 6y ago
  My understanding 30 years ago was a "PAD" was the TCP/IP equivalent of a "terminal server", translating serial streams to network connections. This may be an overly simplistic view, I don't know. It's been a very long time! Are there any public x.25 networks still operating?
  - non-entity 6y ago
    > Are there any public x.25 networks still operating? Not that I know of. My plan if to use old line simulators and other tools i can find on ebay and telcom equipment reseller sites to create a "fake" private one. This is one of those projects that I'm working on purely out of novelty interest :P.
    - icedchai 6y ago
      Sounds cool! Perhaps you could create the x.25 equivalent of HECNet, the hobbyist DECnet.

rjsw 6y ago

OSI could run over X.25. As you say, it doesn't mandate dumb terminals. I worked for a couple of startups that ran services over X.25. One road not taken could have been to define a structured document format in ASN.1 that would be displayed by the terminal.

eternalban 6y ago

You are confusing connection-oriented phase of x.25 with “streams”. X.25 is a “packet-switched” “connection-oriented” protocol. [which p.s. makes sense for traditional telecom’s view of the world, which as you know is circuit-switched. One of the main beefs of telcos in regards to IP was traffic management. Compare X.25 congestion management with IP. ] Some kind soul has delved into the details of modalities of networking protocols: https://stackoverflow.com/a/43543284 https://stackoverflow.com/a/43543284

C1sc0cat 6y ago

I think its more correct to say x.25 was virtual circuit based - over a packet based system. x.25 had a MFT (Metric Fuck Ton) of error checking (at each layer). I used to work in OSI based networking - debugging OSI issues was an art - no wireshark back then However You could do some cool things with osi based networking binary attachments natively supported, years before the internet had it. Interworking between legacy system like Telex, I used to have my own telex number and answerback and could have had an x.400 email address at the country level. Ps id take site you linked with pinch of salt no mention of PAD's for example.