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SubjectRe: bug causes tcp/ip stack corruption
Hi all.

>> On all modem I know the ``+++'' string has to be preceeded and
>> followed by a second pause; the exact length is configurable.
>> Since SLIP and PPP packets are always longer than three bytes,
>> this should not ever happen?

> You know that, I know that. Piles of crap modem makes apparently
> dont

The official Prestel modem from way back had a curious 'feature' in
this respect: If it received the sequence '+++' following a pause in
excess of 1.5 seconds (the fixed delay on that particular model), it
then paused for 1.5 seconds, queueing up any characters that arrived
during the pause without sending them. If, at the end of that pause,
its buffer was empty, it knew to switch to command mode, otherwise it
just sent all the characters that had arrived to the far end...use it
with a system set to echo characters back, and the modem at the far
end is highly likely to switch to command mode...

Another thing worth noting is that the character used in that string
is programmable on most modern modems, with '+' being the default. If
something changes that character, some other sequence of three
consecutive identical characters will result in the same behaviour
whilst '+++' will have no effect...

Best wishes from Riley.

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