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Comment by jmspring | Hacker News Reader

The funny thing is, the AT / Hayes Command Set still shows up in semi-recent cellular modems. Did some work with an embedded system using FreeRTOS and it had a cellular modem for sending data. I don't recall all the nuances as it was about 6 years ago, but I was surprised to see it show up as I had to write a very dumb http client for it to send some data from a ODBII dongle to a web service collecting the data for a PoC.

I had no control over the hardware design, one of the more annoying / interesting projects I had had in awhile though.

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Yep GSM standardized on some of the Hayes AT commands and added many new AT commands. Considering GSM was published in 1990, that means they were working on it in the 1980s when these commands were regularly used. I imagine there's no strong incentive to update these commands and they keep getting migrated to whatever new voice and data protocol cellular systems tend to use when it comes to modem interfaces. I guess no one wants to sell an incompatible modem to OEMs, so these old AT commands will probably always be with us.

I remember seeing this a few years ago in some mifi device or something and thinking "Wait are those old modem commands?" I realized, well, that is a modem being used, so they probably just reused old protocols because why not?

List of commands for those interested:

https://www.electronicsforu.com/resources/gsm-at-commands

Not sure if there is a better reason, but I think things like this just end up sticking around due to ossification. Almost anything (desktop/embedded OS, routers, ..) with a PPP stack will be built to work with modems with AT command sets, so new modems built to handle a PPP stack will still end up implement AT commands. Meanwhile if it's not broke, why fix it? It looks like the ATDT command has worked since 1981.

All of at least Huawei's 3G/4G dongles still support this mode, and would expect it's the same for pretty much any other vendor.

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