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I wrote a "ring knocking" tool back in my college days so that I could connect to my Linux box at home from the labs at school since I was on dial-up. I'd go to

I wrote a "ring knocking" tool back in my college days so that I could connect to my Linux box at home from the labs at school since I was on dial-up. I'd go to the payphone, put in a quarter, call my line and let it ring the requisite number of times, hang up, get my quarter back, then go to the lab and check my school email account. The ringconnectd daemon would detect the rings, wait a few seconds, connect to my ISP, and mail me its current IP address. It was my second open source project: https://www.ibiblio.org/pub/Linux/system/network/daemons/ringconnectd.lsm https://www.ibiblio.org/pub/Linux/system/network/daemons/rin... I was still getting support requests for it in the late 2000s from people who were using it in South Africa :)

numlock86 6y ago
I tried to do something similar not too long ago. Different application really, but I wanted to do something on the other end depending on how often it rang. Sadly I discovered that apparently in all-digital "modern" phone networks (SIP, VoIP etc.) the ringing tone you hear as a caller is simply ingested by your network operator and the tone you hear as the one getting called is basically just some audio file that plays over and over, triggered by a single "hey, someone is calling now!"-message sent by a modem unit, which to my surprise are still using AT commands to this day. Bummer. Turns out even the duration of how long it rings depends on too many factors, so what you hear on one end (ringing) might be off by multiple seconds on the other end. At least it explains the "You only heard it ring once? I let it ring like five times before I hung up! Seriously!"-anecdotes I keep picking up. :)
- kwent 6y ago
  This is also true with silences. When we switched from analogue phone calls to digital phone calls in the 90's, SIP began to ingest white noise during silences due to discomfort perceived by the users thinking they got hung up or the network has been disconnected.
  - eru 6y ago
    It's even worse on Zoom. A simple experiment: let your counter party put a metronome next to their microphone, and enjoy the time distortion.
    - HenryBemis 6y ago
      It is more fun in Skype calls. There is a 'gap' then you get a 10second audio clip 'played to you' in 5 seconds :)
  - deleted 6y ago
    [deleted]
- B1FF_PSUVM 6y ago
  > simply ingested by your network operator That's an amusing typo - I suppose that should be 'injected', but Pac-Man pops to mind ...
- lxgr 6y ago
  > the ringing tone you hear as a caller is simply ingested by your network operator In my experience this depends on the network in question: SIP supports "early media" and I've seen it in action a few times. You can tell by the fact that phone UIs usually don't count connection time in that state, yet you can hear a prerecorded announcement, music mixed with the dialing tone etc. I remember some creative uses of this as well: If you controlled the signalling stack, it was possible to keep a connection open in this state indefinitely without either end getting charged. Here's a relevant RFC: https://tools.ietf.org/html/rfc3960 https://tools.ietf.org/html/rfc3960
  - viraptor 6y ago
    The early media can still be generated at any point of the calling chain. It doesn't have to correspond to actual ringing, if ringing does happen on the POTS side. (For a test, you can call someone in the UK and check if you hear Pink Floyd style beeps)

numlock86 6y ago

I tried to do something similar not too long ago. Different application really, but I wanted to do something on the other end depending on how often it rang. Sadly I discovered that apparently in all-digital "modern" phone networks (SIP, VoIP etc.) the ringing tone you hear as a caller is simply ingested by your network operator and the tone you hear as the one getting called is basically just some audio file that plays over and over, triggered by a single "hey, someone is calling now!"-message sent by a modem unit, which to my surprise are still using AT commands to this day. Bummer. Turns out even the duration of how long it rings depends on too many factors, so what you hear on one end (ringing) might be off by multiple seconds on the other end. At least it explains the "You only heard it ring once? I let it ring like five times before I hung up! Seriously!"-anecdotes I keep picking up. :)

kwent 6y ago
This is also true with silences. When we switched from analogue phone calls to digital phone calls in the 90's, SIP began to ingest white noise during silences due to discomfort perceived by the users thinking they got hung up or the network has been disconnected.
- eru 6y ago
  It's even worse on Zoom. A simple experiment: let your counter party put a metronome next to their microphone, and enjoy the time distortion.
  - HenryBemis 6y ago
    It is more fun in Skype calls. There is a 'gap' then you get a 10second audio clip 'played to you' in 5 seconds :)
- deleted 6y ago
  [deleted]
B1FF_PSUVM 6y ago
> simply ingested by your network operator That's an amusing typo - I suppose that should be 'injected', but Pac-Man pops to mind ...
lxgr 6y ago
> the ringing tone you hear as a caller is simply ingested by your network operator In my experience this depends on the network in question: SIP supports "early media" and I've seen it in action a few times. You can tell by the fact that phone UIs usually don't count connection time in that state, yet you can hear a prerecorded announcement, music mixed with the dialing tone etc. I remember some creative uses of this as well: If you controlled the signalling stack, it was possible to keep a connection open in this state indefinitely without either end getting charged. Here's a relevant RFC: https://tools.ietf.org/html/rfc3960 https://tools.ietf.org/html/rfc3960
- viraptor 6y ago
  The early media can still be generated at any point of the calling chain. It doesn't have to correspond to actual ringing, if ringing does happen on the POTS side. (For a test, you can call someone in the UK and check if you hear Pink Floyd style beeps)