4 ms·

Sweet, I've been looking for one of these to test CSD calls out for the first time in like 20 years before GSM gets shut down on T-Mobile. There was one other s

Sweet, I've been looking for one of these to test CSD calls out for the first time in like 20 years before GSM gets shut down on T-Mobile. There was one other service in Vancouver that probably shut down last year but I'm not sure data calls work internationally. EDIT: This is that service if you are a Canadian that wants to try it, https://www2.vcn.bc.ca/free-internet-access-via-dial-up/ https://www2.vcn.bc.ca/free-internet-access-via-dial-up/

lxgr 3y ago
Could you theoretically use an analog modem (or worst case an acoustic coupler) over IMS (VoLTE etc., which should all have at least some QoS), or are the jitter rates and codecs too bad for that (like they often are for Fax over VoIP on fixed lines)? I wonder if some of the networks that are continuing to offer GSM (usually via some core network emulations, as far as I understand, to make it more compatible with modern core networks) have already broken CSD for similar reasons.
- joecool1029 3y ago
  Theoretically, maybe. If you got a good 'HD voice' (higher bitrate EVS codec) call, it's possible you could negotiate and send a slower fax signal. No way on a full-rate or half-rate GSM codec or amr-nb though, just doesn't have the bandwidth, chops too much. Even back in the early 2000's when I was using free nights and weekends with my T68i to make calls to a free dialup provider in new england (9600baud yea), my call would still drop every hour or so just due to signal hiccups. (T-Mobile never enabled HS-CSD for 28.8kbps using more timeslots and it's unlikely my current rate plan will allow for CSD calls, but it doesn't mean I won't try, I still have an old sim card able to be used in 2G only phones, including that very same t68i which I tested last summer, still works.)
  - dylan604 3y ago
    I thought VoIP codecs all chopped the frequencies that seems like it would be very detrimental to a data signal. Is the "HD" quality high enough for that, or was the analog data signal not as full frequency as I'm thinking they would be?
    - wolrah 3y ago
      Most internet-based VoIP services (read: full telephone providers, not just chat providers) use the same exact G.711 codecs used in the digital portions of traditional telephone lines for normal calls. In theory you can run anything over this that could run over a long distance PSTN link. In practice most modem technologies do not handle jitter and packet loss well at all, and quirks which a human would not even notice will trip up a data call. It still works, I have clients running credit card machines on VoIP lines all day, but the longer the call and the higher the bandwidth the more likely something is to go wrong. A short 9600bps data exchange from a card machine is a lot easier than a 30 page 33.6k fax which is a lot easier than a 56k modem on a PC. There's a special method called T.38 that allows VoIP providers with compatible endpoints to convert digital fax calls back to a data stream instead of audio which makes it a lot more tolerant of delay and jitter as well as slightly more tolerant of loss. Something similar could hypothetically be done for data modems but I haven't seen it.
      - AvocadoPanic 3y ago
        v.150.1
      - throwaway67743 3y ago
        You want 722 really, one of the choices for "HD voice", it mangles it much less than even 711
        lxgr 3y ago
        No, unlike G.711, G.722 is lossily compressed using psychoacoustic concepts, and modems wouldn’t know what to do with the extra acoustic frequencies anyway. G.722 might sound better to humans, but G.711 is definitely better for modems since it’s effectively just uncompressed PCM (disregarding a bit of dynamic range compression which modems are generally fine with).
        throwaway67743 3y ago
        It is compressed, yes, but at higher bitrates it is actually usable for modems/faxes, you're limited to low baud rates anyway due to jitter and sample intervals. But really the benefit is 16k sampling rate instead of 8, I'm not saying it's great but it's the best we've got. It would be possible to mask this with a relatively simple FXS device to hide all of this and pretend it's a modem while packetising the actual data, but I guess the demand is almost zero so why bother. I've been looking for a solution for many years to retain dialin services without having racks full of modems and trunks that are rapidly going out of fashion and at some point will not be available except via IP (and now we have the same problem at both ends), but they just don't exist.
  - porkbeer 3y ago
    Ive gotten 2400 and occasionally 9600 over audio voip. Ymmv.
  - joecool1029 3y ago
    So I looked into it (too late for me to edit), if you have a government account it might be possible to add CSDOPTION to your account for $9.99/mo. It's highly unlikely though, I found the old and current price schedules and this was removed from it. Old gov contract expired 2022: https://www.gsaadvantage.gov/ref_text/GS35F0503M/0VX37Z.3RNG6Q_GS35F0503M_GS-35F-0503M-2-5-2021-653292.PDF https://www.gsaadvantage.gov/ref_text/GS35F0503M/0VX37Z.3RNG... (search for CSD, it's there) New gov contract in effect (no CSD): https://www.gsaadvantage.gov/ref_text/47QTCA22D008N/0YTCAI.3UJP56_47QTCA22D008N_47QTCA22D008NPRICELIST09112023.PDF https://www.gsaadvantage.gov/ref_text/47QTCA22D008N/0YTCAI.3... EDIT: I tried to CSD dialup using my K850i which can handle my new and older SIM cards, no good. Simple Choice plans are way too new for this (the old plan I had in the early-mid 2000's was the Get More one)
- grishka 3y ago
  We still have 2G on all carriers in Russia with no plans to shut it down (no plans to introduce 5G either though). But I'm not sure there are any operational dial-up providers left I could test CSD with. But I am now curious to test it.
deleted 3y ago
[deleted]

lxgr 3y ago

Could you theoretically use an analog modem (or worst case an acoustic coupler) over IMS (VoLTE etc., which should all have at least some QoS), or are the jitter rates and codecs too bad for that (like they often are for Fax over VoIP on fixed lines)? I wonder if some of the networks that are continuing to offer GSM (usually via some core network emulations, as far as I understand, to make it more compatible with modern core networks) have already broken CSD for similar reasons.

joecool1029 3y ago
Theoretically, maybe. If you got a good 'HD voice' (higher bitrate EVS codec) call, it's possible you could negotiate and send a slower fax signal. No way on a full-rate or half-rate GSM codec or amr-nb though, just doesn't have the bandwidth, chops too much. Even back in the early 2000's when I was using free nights and weekends with my T68i to make calls to a free dialup provider in new england (9600baud yea), my call would still drop every hour or so just due to signal hiccups. (T-Mobile never enabled HS-CSD for 28.8kbps using more timeslots and it's unlikely my current rate plan will allow for CSD calls, but it doesn't mean I won't try, I still have an old sim card able to be used in 2G only phones, including that very same t68i which I tested last summer, still works.)
- dylan604 3y ago
  I thought VoIP codecs all chopped the frequencies that seems like it would be very detrimental to a data signal. Is the "HD" quality high enough for that, or was the analog data signal not as full frequency as I'm thinking they would be?
  - wolrah 3y ago
    Most internet-based VoIP services (read: full telephone providers, not just chat providers) use the same exact G.711 codecs used in the digital portions of traditional telephone lines for normal calls. In theory you can run anything over this that could run over a long distance PSTN link. In practice most modem technologies do not handle jitter and packet loss well at all, and quirks which a human would not even notice will trip up a data call. It still works, I have clients running credit card machines on VoIP lines all day, but the longer the call and the higher the bandwidth the more likely something is to go wrong. A short 9600bps data exchange from a card machine is a lot easier than a 30 page 33.6k fax which is a lot easier than a 56k modem on a PC. There's a special method called T.38 that allows VoIP providers with compatible endpoints to convert digital fax calls back to a data stream instead of audio which makes it a lot more tolerant of delay and jitter as well as slightly more tolerant of loss. Something similar could hypothetically be done for data modems but I haven't seen it.
    - AvocadoPanic 3y ago
      v.150.1
    - throwaway67743 3y ago
      You want 722 really, one of the choices for "HD voice", it mangles it much less than even 711
      - lxgr 3y ago
        No, unlike G.711, G.722 is lossily compressed using psychoacoustic concepts, and modems wouldn’t know what to do with the extra acoustic frequencies anyway. G.722 might sound better to humans, but G.711 is definitely better for modems since it’s effectively just uncompressed PCM (disregarding a bit of dynamic range compression which modems are generally fine with).
        throwaway67743 3y ago
        It is compressed, yes, but at higher bitrates it is actually usable for modems/faxes, you're limited to low baud rates anyway due to jitter and sample intervals. But really the benefit is 16k sampling rate instead of 8, I'm not saying it's great but it's the best we've got. It would be possible to mask this with a relatively simple FXS device to hide all of this and pretend it's a modem while packetising the actual data, but I guess the demand is almost zero so why bother. I've been looking for a solution for many years to retain dialin services without having racks full of modems and trunks that are rapidly going out of fashion and at some point will not be available except via IP (and now we have the same problem at both ends), but they just don't exist.
- porkbeer 3y ago
  Ive gotten 2400 and occasionally 9600 over audio voip. Ymmv.
- joecool1029 3y ago
  So I looked into it (too late for me to edit), if you have a government account it might be possible to add CSDOPTION to your account for $9.99/mo. It's highly unlikely though, I found the old and current price schedules and this was removed from it. Old gov contract expired 2022: https://www.gsaadvantage.gov/ref_text/GS35F0503M/0VX37Z.3RNG6Q_GS35F0503M_GS-35F-0503M-2-5-2021-653292.PDF https://www.gsaadvantage.gov/ref_text/GS35F0503M/0VX37Z.3RNG... (search for CSD, it's there) New gov contract in effect (no CSD): https://www.gsaadvantage.gov/ref_text/47QTCA22D008N/0YTCAI.3UJP56_47QTCA22D008N_47QTCA22D008NPRICELIST09112023.PDF https://www.gsaadvantage.gov/ref_text/47QTCA22D008N/0YTCAI.3... EDIT: I tried to CSD dialup using my K850i which can handle my new and older SIM cards, no good. Simple Choice plans are way too new for this (the old plan I had in the early-mid 2000's was the Get More one)
grishka 3y ago
We still have 2G on all carriers in Russia with no plans to shut it down (no plans to introduce 5G either though). But I'm not sure there are any operational dial-up providers left I could test CSD with. But I am now curious to test it.

deleted 3y ago

[deleted]