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One thing the article doesn't really cover is how Hayes solved the problem of it being extremely hard to avoid +++ appearing in th data stream - Hayes required
by mjg59 5y ago
One thing the article doesn't really cover is how Hayes solved the problem of it being extremely hard to avoid +++ appearing in th data stream - Hayes required that there be a pause where no data was sent both before after the +++ before it would transition into command mode, and otherwise would just continue in data mode. Hayes patented this and charged other modem manufacturers to license it - not everyone was willing to pay, so an alternative approach was to change the behaviour to only transition to command mode on +++(valid AT command), which is the reason sending IRC CTCP PING messages containing +++ATH0 was effective at dropping people off IRC (the incoming +++ATH0 did nothing, but the IRC client would then send it back and the modem would drop if it didn't implement the Hayes solution).
Thanks, Hayes. Thayes.
- kmeisthax 5y agoctcp ping +++ATFYPM
- brewtide 5y agos2=255 in the INIT string of modem. Solved! (If I remember correctly).
- mrlonglong 5y agoAka ping of death. Fun. NOT!
- DoneWithAllThat 5y agoWhat are birds? We just don’t know.
- jcrawfordor 5y agoThe pause after +++ was really sort of a hack to resolve race condition problems (entering command mode when the modem still had inbound data in buffer) rather than any kind of security measure, but it did have the upside of making it a little more difficult to get a modem to switch to command mode unintentionally. There were various other solutions to this problem but for the most part it didn't completely go away until the practice of moving data over the Hayes interface became uncommon.