3 ms·

A software version of a mercury delay line! https://en.wikipedia.org/wiki/Delay-line_memory https://en.wikipedia.org/wiki/Delay-line_memory

EvanAnderson 10mo ago
Yep. ICMP delay line memory.
- cbdevidal 10mo ago
  Okay, but could someone ELI5 how it works? Because I am heckin’ confused
  - adzm 10mo ago
    Imagine a continuously-moving loop that stores bits. When you want a certain bit you just wait for it to loop back to the position you want.
    - cbdevidal 10mo ago
      Good, but how does a ping hold data? AFAIK each ping is a single round trip and not a continuous loop. And where in the packet is the data stored?
      - deleted 10mo ago
        [deleted]
      - lesuorac 10mo ago
        In everybody else's router as it travels back and forth. Imagine mailing somebody a letter with data; once they receive the letter they send it back. The information is stored within the postal system.
      - robjs 10mo ago
        ICMP packets pretty much always carry some data (even though it's not _strictly_ required). This data is what is padded when the user asks for a ping with a specific packet size (e.g., when debugging MTU issues). In some applications, using an ICMP payload and getting a quote of the IP header + 8-bytes of the original packet back in ICMP error messages is part of the application. For example, traceroute utilises the fact that it gets part of the payload back in a ICMP TTL exceeded message to identify _which_ traceroute request was being responded to.
      - chasd00 10mo ago
        you're right it's not continuous, you'd have to send another ping once the first one is finished. Your data is only "stored in the network" until the ping completes which would be a few hundred ms or so and then another ping has to be sent. If a single ping fails i wonder if the whole "fs" is corrupted or if there some kind of error handling built in.
        EvanAnderson 10mo ago
        Clearly you need to send multiple redundant PINGs. ICMP delay line memory RAID.
  - leoc 10mo ago
    The UK's National Musuem of Computing has a nice demonstration video https://www.youtube.com/watch?v=xGEAPVCuwvY https://www.youtube.com/watch?v=xGEAPVCuwvY . Apparently delay-line memory also went on to have wide use in colour TVs before the arrival of cheap semiconductor memory https://www.youtube.com/watch?v=EPQq7xd3WdA https://www.youtube.com/watch?v=EPQq7xd3WdA , which was quite appropriate as it had come from radar in the first place https://www.youtube.com/watch?v=JZLpbhsE72I&t=675s https://www.youtube.com/watch?v=JZLpbhsE72I&t=675s .

EvanAnderson 10mo ago

Yep. ICMP delay line memory.

cbdevidal 10mo ago
Okay, but could someone ELI5 how it works? Because I am heckin’ confused
- adzm 10mo ago
  Imagine a continuously-moving loop that stores bits. When you want a certain bit you just wait for it to loop back to the position you want.
  - cbdevidal 10mo ago
    Good, but how does a ping hold data? AFAIK each ping is a single round trip and not a continuous loop. And where in the packet is the data stored?
    - deleted 10mo ago
      [deleted]
    - lesuorac 10mo ago
      In everybody else's router as it travels back and forth. Imagine mailing somebody a letter with data; once they receive the letter they send it back. The information is stored within the postal system.
    - robjs 10mo ago
      ICMP packets pretty much always carry some data (even though it's not _strictly_ required). This data is what is padded when the user asks for a ping with a specific packet size (e.g., when debugging MTU issues). In some applications, using an ICMP payload and getting a quote of the IP header + 8-bytes of the original packet back in ICMP error messages is part of the application. For example, traceroute utilises the fact that it gets part of the payload back in a ICMP TTL exceeded message to identify _which_ traceroute request was being responded to.
    - chasd00 10mo ago
      you're right it's not continuous, you'd have to send another ping once the first one is finished. Your data is only "stored in the network" until the ping completes which would be a few hundred ms or so and then another ping has to be sent. If a single ping fails i wonder if the whole "fs" is corrupted or if there some kind of error handling built in.
      - EvanAnderson 10mo ago
        Clearly you need to send multiple redundant PINGs. ICMP delay line memory RAID.
- leoc 10mo ago
  The UK's National Musuem of Computing has a nice demonstration video https://www.youtube.com/watch?v=xGEAPVCuwvY https://www.youtube.com/watch?v=xGEAPVCuwvY . Apparently delay-line memory also went on to have wide use in colour TVs before the arrival of cheap semiconductor memory https://www.youtube.com/watch?v=EPQq7xd3WdA https://www.youtube.com/watch?v=EPQq7xd3WdA , which was quite appropriate as it had come from radar in the first place https://www.youtube.com/watch?v=JZLpbhsE72I&t=675s https://www.youtube.com/watch?v=JZLpbhsE72I&t=675s .